bench: concurrent reads re-measured after the read fixes

Idle tank at 408f69e, h5py re-run in the same session. Contiguous reads
went from 0.25x to 1.44x h5py (full) and 0.12x to 6.3x (256x256
hyperslabs) on one thread; deflate full reads at 8 threads 887 -> 2943
MB/s (h5py processes 3042). Full chunked reads at 16 threads are still
0.69x-0.76x h5py processes; the issue stays open.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

.gitea/workflows/ci.yml

@@ -9,31 +9,45 @@ jobs:
     runs-on: ubuntu-latest
     container: rust:latest
     steps:
-      - uses: actions/checkout@v4
-      - name: Cache cargo registry/target
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cargo/registry
-            ~/.cargo/git
-            target
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+      # Plain git rather than actions/checkout: that is a JavaScript action,
+      # and rust:latest has no `node`, so it failed with exit 127 before any
+      # code was built — on every push. actions/cache went for the same reason.
+      - name: Check out
+        run: |
+          git init -q .
+          git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
+          for i in 1 2 3; do git fetch -q --depth 1 origin "${GITHUB_SHA}" && break; sleep 5; done
+          git checkout -q FETCH_HEAD
       - name: Install rustfmt & clippy components
         run: rustup component add rustfmt clippy
       - name: Install thumbv7em-none-eabihf target
         run: rustup target add thumbv7em-none-eabihf
+      - name: Install wasm32-unknown-unknown target
+        # ci-test.sh builds the reader and clawhdf5-wasm for the browser.
+        run: rustup target add wasm32-unknown-unknown
       - name: Install Python interop dependencies
         # The interop suites used to skip silently when python3/h5py were
         # missing, so they never ran in CI. Install them and make a missing
         # dependency a failure (CLAWHDF5_REQUIRE_INTEROP below).
         run: |
           apt-get update
-          apt-get install -y --no-install-recommends python3 python3-venv
+          # cmake builds libz-ng-sys for the opt-in `fast-deflate` (zlib-ng)
+          # steps in ci-test.sh; rust:latest does not ship it. The default
+          # build (pure-Rust zlib-rs) does not need it.
+          # hdf5-tools: h5ls/h5stat/h5dump/h5diff, which the h5rs
+          # (clawhdf5-tools) interop tests compare against.
+          apt-get install -y --no-install-recommends python3 python3-venv cmake hdf5-tools
           python3 -m venv /opt/interop
-          /opt/interop/bin/pip install --no-cache-dir h5py numpy netCDF4 xarray
+          # maturin + pytest: ci-test.sh builds the Python package
+          # (crates/clawhdf5-py) and runs its tests against h5py.
+          /opt/interop/bin/pip install --no-cache-dir h5py numpy netCDF4 xarray hdf5plugin maturin pytest
           echo "/opt/interop/bin" >> "$GITHUB_PATH"
       - name: Show interop library versions
-        run: /opt/interop/bin/python -c "import h5py, netCDF4; print('h5py', h5py.__version__, 'HDF5', h5py.version.hdf5_version, 'netCDF4', netCDF4.__version__)"
+        # h5dump's version too: the h5rs dump test requires its exact output
+        # (checked against Debian's 1.14.5 in rust:latest and 1.14.6).
+        run: |
+          /opt/interop/bin/python -c "import h5py, netCDF4, hdf5plugin; print('h5py', h5py.__version__, 'HDF5', h5py.version.hdf5_version, 'netCDF4', netCDF4.__version__, 'hdf5plugin', hdf5plugin.version)"
+          h5dump --version
       - name: Run CI script
         env:
           # Name the interpreter outright rather than relying on $GITHUB_PATH
@@ -44,3 +58,40 @@ jobs:
           CLAWHDF5_PYTHON: /opt/interop/bin/python
           CLAWHDF5_REQUIRE_INTEROP: "1"
         run: bash scripts/ci-test.sh
+
+  test-arm64:
+    # The aarch64 kernels in clawhdf5-accel — NEON `dot_i8`, including the
+    # SDOT path, and the f32 NEON kernels — are cfg'd out on x86, so the job
+    # above never compiles, lints or tests them.
+    #
+    # `linux_arm64` is served by two runners that execute differently:
+    # vision-01 runs steps on the host (Rust already installed) and vision-02
+    # runs them in docker.gitea.com/runner-images. So the steps work in both:
+    # no `container:`, no JavaScript actions (they are fetched from GitHub,
+    # which not every runner reliably reaches), and an explicit `+stable`
+    # toolchain rather than whatever a host happens to default to.
+    runs-on: linux_arm64
+    env:
+      CARGO_NET_RETRY: "10"
+      CARGO_TERM_COLOR: always
+    steps:
+      - name: Check out
+        run: |
+          git init -q .
+          git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
+          for i in 1 2 3; do git fetch -q --depth 1 origin "${GITHUB_SHA}" && break; sleep 5; done
+          git checkout -q FETCH_HEAD
+      - name: Rust stable
+        run: |
+          export PATH="$HOME/.cargo/bin:$PATH"
+          command -v rustup >/dev/null || curl -sSf --retry 5 https://sh.rustup.rs | sh -s -- -y --profile minimal --default-toolchain none
+          rustup toolchain install stable --profile minimal --component clippy
+          echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
+      - name: Confirm aarch64
+        run: |
+          test "$(uname -m)" = aarch64
+          if grep -q asimddp /proc/cpuinfo; then echo "dot-product extension present: SDOT kernel runs"; else echo "no dot-product extension: plain NEON kernel runs"; fi
+      - name: Clippy (aarch64 kernels)
+        run: cargo +stable clippy -p clawhdf5-accel --all-targets -- -D warnings
+      - name: Test
+        run: cargo +stable test -p clawhdf5-accel -p clawhdf5-ann -p clawhdf5-format

.gitea/workflows/conformance.yml

@@ -0,0 +1,56 @@
+name: Conformance
+# Nightly: read every file of the pinned public HDF5 corpora with clawhdf5 and
+# with h5py/libhdf5 and compare (conformance/run.sh; CONFORMANCE.md explains
+# the method). Fails on any panic, hang, crash or out-of-memory in clawhdf5,
+# and when the ok count drops below conformance/baseline.json or a file the
+# baseline lists as ok stops being ok. The report is printed into the job log;
+# nothing is uploaded (artifact actions are JavaScript, which rust:latest
+# cannot run — see CLAUDE.md).
+on:
+  schedule:
+    - cron: "17 3 * * *"
+  workflow_dispatch:
+jobs:
+  conformance:
+    runs-on: ubuntu-latest
+    container: rust:latest
+    timeout-minutes: 60
+    env:
+      CARGO_NET_RETRY: "10"
+    steps:
+      # Plain git, not actions/checkout (a JavaScript action; see ci.yml).
+      - name: Check out
+        run: |
+          git init -q .
+          git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
+          for i in 1 2 3; do git fetch -q --depth 1 origin "${GITHUB_SHA}" && break; sleep 5; done
+          git checkout -q FETCH_HEAD
+      - name: Install h5py, h5dump and the probe's codec libraries
+        # hdf5-tools: h5dump for the CVE-corpus comparison. libaec-dev and
+        # pkg-config: the probe builds clawhdf5-format with `szip` (the core
+        # crates' default build needs neither).
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends python3 python3-venv hdf5-tools libaec-dev pkg-config
+          python3 -m venv /opt/conformance
+          /opt/conformance/bin/pip install --no-cache-dir -r conformance/requirements.txt
+          /opt/conformance/bin/python -c "import h5py, hdf5plugin; print('h5py', h5py.__version__, 'HDF5', h5py.version.hdf5_version, 'hdf5plugin', hdf5plugin.version)"
+          h5dump --version
+      - name: Probe unit tests
+        run: cargo test --release --manifest-path conformance/probe/Cargo.toml
+        env:
+          CARGO_TARGET_DIR: conformance/.cache/target
+      - name: Sweep
+        # The corpora come from GitHub (pinned commits, conformance/corpus.txt),
+        # so this job needs a runner that reaches github.com.
+        env:
+          CLAWHDF5_PYTHON: /opt/conformance/bin/python
+        run: bash conformance/run.sh
+      - name: Report
+        if: always()
+        run: |
+          if [ -f CONFORMANCE.md ]; then cat CONFORMANCE.md; else echo "no report was generated"; fi
+          if [ -f conformance/.cache/results/summary.md ]; then
+            echo; echo "---- per-file detail (conformance/.cache/results/summary.md) ----"
+            cat conformance/.cache/results/summary.md
+          fi

.gitignore

@@ -5,3 +5,5 @@ benchmarks/longmemeval/*.json
 # Local model weights (MiniLM etc.) — large, not committed
 weights/
 .venv
+__pycache__/
+.pytest_cache/

CLAUDE.md

@@ -1,33 +1,40 @@
 # clawhdf5
 
 ## Purpose
-Pure-Rust HDF5 format implementation with HNSW vector search, WAL-backed persistence, agent memory storage, and GPU-accelerated I/O. Used by ZeroClaw as its persistent memory and knowledge graph backend.
+Pure-Rust HDF5 format implementation with HNSW vector search, WAL-backed persistence, agent memory storage, and GPU-accelerated vector search. A standalone library. Its one verified consumer is ClawBrainHub (`.brain` files); no agent framework integrates it (OpenClaw and ZeroClaw claims were withdrawn on 2026-09-25 — neither was ever true).
 
 ## Architecture
 
-Cargo workspace with 16 crates under `crates/` (plus `libaec-sys`, an internal FFI bindings crate for the optional `szip` feature):
+Cargo workspace with 18 crates under `crates/` (plus `libaec-sys`, an internal FFI bindings crate for the optional `szip` feature):
 
 | Crate | Role |
 |-------|------|
 | `clawhdf5-format` | HDF5 binary spec parser (superblock, B-tree, heap) — also holds shared type definitions and physical constants |
 | `clawhdf5-io` | Read/write implementation |
-| `clawhdf5-filters` | Compression filters (gzip, LZ4, Zstd, Blosc) |
+| `clawhdf5-filters` | Deflate backends (zlib-rs, zlib-ng, Apple Compression); the HDF5 filter pipeline, the filter registry (`clawhdf5_format::filter_registry`) and the other codecs (LZ4, Zstd, SZIP, N-Bit, scale-offset, pcodec, and the pure-Rust plugin filters LZF, bitshuffle, bzip2, Blosc 1) live in `clawhdf5-format`. No Blosc2 or ZFP. |
 | `clawhdf5-derive` | Proc-macro derive for HDF5-serializable structs |
 | `clawhdf5` | Main facade crate |
 | `clawhdf5-netcdf4` | NetCDF-4 compatibility layer |
 | `clawhdf5-ann` | HNSW approximate nearest-neighbor vector index |
 | `clawhdf5-agent` | Agent memory, session history, knowledge graph storage |
-| `clawhdf5-gpu` | GPU-accelerated I/O via wgpu (hand-written WGSL compute shaders) |
+| `clawhdf5-gpu` | GPU vector distance computation via wgpu (hand-written WGSL compute shaders) — not dataset I/O |
 | `clawhdf5-accel` | CPU SIMD acceleration path |
-| `clawhdf5-migrate` | Schema migration engine |
+| `clawhdf5-migrate` | SQLite → HDF5 agent-memory migration |
 | `clawhdf5-android` | Android JNI bindings |
-| `clawhdf5-cli` | Command-line interface |
+| `clawhdf5-cli` | Command-line interface (agent memory) |
+| `clawhdf5-tools` | `h5rs`: pure-Rust HDF5 tools — `ls`, `dump` (DDL / hdf5-json), `stat`, `diff`, `check` (structural + checksum validator) |
 | `clawhdf5-napi` | Node.js native addon bindings |
 | `clawhdf5-py` | PyO3 Python bindings |
+| `clawhdf5-wasm` | WebAssembly (wasm-bindgen) reader for the browser; demo in `examples/wasm-viewer/` |
 | `clawhdf5-bench` | Benchmark suite |
 
 ## Key Features
-- Zero-dependency HDF5 read/write (no libhdf5 C library required)
+- Zero-C-dependency HDF5 read/write: no libhdf5, and deflate defaults to
+  pure-Rust zlib-rs (`fast-deflate` opts into zlib-ng, which needs cmake).
+  `ci-test.sh` fails if a C-building crate enters the core crates' default
+  tree. flate2 must keep `runtime_detection` with zlib-rs — without it zlib-rs
+  loses SIMD and inflates 3.5x slower. MSRV is 1.92 (`rust-version`, checked
+  in CI).
 - HNSW vector index for semantic similarity search over agent memories — the
   `clawhdf5-agent` `hnsw` feature is **on by default**, so `hybrid_search` uses
   the approximate `clawhdf5-ann` index for the vector stage (the index mirrors
@@ -39,13 +46,20 @@ Cargo workspace with 16 crates under `crates/` (plus `libaec-sys`, an internal F
   (plain closest-M capped recall on clustered data: 0.31 recall@10 at 100K). Its
   graph is saved to `<store>.h5.ann` at each checkpoint and reloaded by `open()`
   (tied to the checkpoint by a generation id; stale/damaged sidecars are
-  ignored and the index rebuilt). `MemoryConfig::quantized_index` (off by
-  default, persisted) stores the index's own copy of the embeddings as `i8`,
+  ignored and the index rebuilt). `MemoryConfig::quantized_index` (**on by
+  default** for new stores, persisted; stores predating the setting load as
+  `false` and keep their f32 index — guarded by
+  `tests/fixtures/store_v2_5_0.h5`; CLI opt-out is `create --f32-index`)
+  stores the index's own copy of the embeddings as `i8`,
   which roughly halves a loaded store's memory (2.72x -> 1.74x the raw vectors
   at 100K); because quantised distances are approximate and `ef` cannot
   compensate, the query path then re-scores the candidate pool against the
-  exact embeddings, which holds recall at the f32 index's level and costs
-  ~13% of QPS. `hybrid_search` keeps one incremental BM25
+  exact embeddings, which holds recall at the f32 index's level. It is also
+  faster at equal recall: 1.63x the QPS on x86-64 (AVX2) and 1.18x on a
+  Raspberry Pi 5 (`clawhdf5_accel::dot_i8`, NEON `SDOT` via inline asm since
+  the intrinsic is unstable; plain NEON on pre-dotprod cores). The aarch64
+  code is `cfg`'d out on x86, so x86 CI never compiles or lints it — test it
+  on real ARM (`rpivision02`, 10.0.2.3, is a Pi 5). `hybrid_search` keeps one incremental BM25
   index for the life of the store and never writes the store: Hebbian
   activation boosts are persisted by the next checkpoint (or on drop), not per
   query. Measure any search-path change with
@@ -75,8 +89,51 @@ Cargo workspace with 16 crates under `crates/` (plus `libaec-sys`, an internal F
   `export` do). An unreadable WAL (torn header, bad magic) is quarantined to
   `<store>.h5.wal.corrupt-<ts>` rather than blocking `open()`; a WAL with an
   unknown *newer* version still fails and is left untouched.
-- `MemoryConfig::compression` uses deflate by default; enable the agent's
-  `zstd` feature to compress embeddings with Zstd instead (links libzstd).
+- `MemoryConfig::float16` (**on by default** for new stores, persisted;
+  existing stores keep their recorded `false` — guarded by the v2.5.0
+  fixture in `tests/float16_store.rs`; CLI opt-out is `create --f32`) writes
+  `/memory/embeddings` as IEEE half precision (48% smaller file at 100K;
+  LongMemEval with real MiniLM embeddings identical to f32).
+  `MemoryCache::half_precision` rounds each embedding as it enters the cache (push, update, WAL replay, and on load of a store still
+  `f32` on disk), so memory and file agree bit for bit; the conversions live
+  in `clawhdf5_format::float16` and must stay the single implementation.
+  Values beyond ±65504 are `MemoryError::InvalidEntry`. Interop: every file
+  must open in h5py — `f32` datasets and empty datasets did not until
+  2026-09-23 (see `docs/known-issues.md`); the agent's `h5py_interop` test
+  guards a whole store.
+- `HDF5Memory::search(query_emb, text, &SearchOptions)` is the full search
+  path: optional source-channel filter (applied before ranking; exact scan of
+  the allowed records whenever cheaper than `pool × M` index distance
+  evaluations, and as the fallback when the pool comes back short), fusion,
+  activation scaling, optional re-ranking and confidence rejection.
+  `hybrid_search`/`hybrid_search_with` are thin wrappers; `ClawhdfBackend`
+  (the `openclaw` module) is `search` with re-rank + confidence on.
+- **OpenClaw is not supported** (decided 2026-09-25): clawhdf5 is not an
+  OpenClaw memory plugin and never was — the old `memory.backend = "clawhdf5"`
+  config was never valid. Don't reintroduce OpenClaw claims; `docs/openclaw.md`
+  records what a real plugin would need.
+- **ZeroClaw does not use clawhdf5** (checked 2026-09-25 against upstream
+  v0.8.5 and the `osobh/zeroclaw` fork, and their full history): no
+  `clawhdf5` feature or backend exists; ZeroClaw's memory backends are
+  sqlite/lucid/postgres/qdrant/markdown/none behind its own `Memory` trait.
+  `clawhdf5-migrate`'s default SQLite layout (`memory_chunks`, `sessions`,
+  `entities`, `relations`) is not ZeroClaw's schema either (ZeroClaw's is a
+  `memories` table). Don't reintroduce integration claims without an
+  integration and a test against the real consumer. Measure changes with
+  `search_harness --options-study`.
+- `MemoryConfig::compression` is off by default; when on, embeddings are
+  deflate-compressed, or Zstd with the agent's `zstd` feature (links libzstd).
+- Signed checkpoints (`clawhdf5-agent` `signing` module): with
+  `HDF5Memory::set_signing_key` every checkpoint stores an Ed25519-signed
+  manifest (SHA-256 per record in a Merkle tree + settings/sessions/graph
+  hashes; per-record hashes in `/integrity/record_hashes`);
+  `HDF5Memory::verify(path, &pk)` locates edits. The hashes must cover exactly
+  what the file persists in the form the loader returns it (strings lose
+  trailing NULs; an empty WAL mark is not written) or untouched stores stop
+  verifying — `tests/signed_store.rs` round-trips awkward strings. The key is
+  never persisted; a signed store refuses to checkpoint without it
+  (`MemoryError::SigningKeyRequired`, and `MemoryError` is `#[non_exhaustive]`).
+  WAL entries after the checkpoint are not covered.
 - `Dataset::verify_provenance()` (clawhdf5 facade, `provenance` feature, on by
   default) recomputes a dataset's SHA-256 and compares it against the
   `_provenance_sha256` attribute written automatically on save when
@@ -93,7 +150,15 @@ Cargo workspace with 16 crates under `crates/` (plus `libaec-sys`, an internal F
   Alerts never block a save — drain them with `HDF5Memory::take_anomaly_alerts`.
   `MemorySource` for this bookkeeping is inferred from the caller-supplied
   `source_channel` string (a heuristic, not an authenticated trust boundary).
-- GPU-accelerated batch I/O for large dataset processing
+- GPU-accelerated vector distance computation (`clawhdf5-gpu`, wgpu); HDF5 I/O itself is CPU-only
+- Browser: `clawhdf5-wasm` (wasm-bindgen, read-only, file held in memory;
+  no Zstd/SZIP since they link C) and the `examples/wasm-viewer/` page.
+  `examples/wasm-viewer/test/run.sh` builds the package (needs the
+  `wasm-bindgen` CLI at the crate's exact version) and tests it under Node
+  and headless Chromium (a Playwright download in `~/.cache/ms-playwright`
+  on tank); the CI container has neither, so CI runs the native
+  `clawhdf5-wasm` `h5py_interop` test on the same fixture. Size numbers are
+  in the example's README.
 - Python and Node.js bindings for cross-language use
 - NetCDF-4 compatibility for scientific data interop
 
@@ -109,12 +174,40 @@ cargo build --release
 cargo test --workspace
 ```
 
+### CI
+`.gitea/workflows/ci.yml` has two jobs, both green as of 2026-09-22:
+- **`test`** (`ubuntu-latest`, in `rust:latest`) runs `scripts/ci-test.sh` with
+  the h5py/netCDF4 interop suites required (`CLAWHDF5_REQUIRE_INTEROP=1`).
+  Served by the `tank` and `architect` runners.
+- **`test-arm64`** (`linux_arm64`) lints and tests the aarch64 code — the NEON
+  kernels are `cfg`'d out on x86, so this is the only place they are built.
+  Served by `vision-01` (host mode) and `vision-02` (Docker), so steps must
+  work in both.
+
+Keep workflows free of JavaScript actions (`actions/checkout`, `actions/cache`,
+…): `rust:latest` has no `node`, and not every runner reaches GitHub, where
+they are fetched from. Check out with plain `git` instead. The `test` job
+installs `cmake` for the opt-in `fast-deflate` (zlib-ng) steps; the default
+build needs no C toolchain, so `test-arm64` does not.
+All runners are on `gitea-runner` 3.5.0, from `docker.gitea.com/act_runner`
+— `gitea/act_runner:latest` on Docker Hub is frozen at 0.6.1.
+
 ### CLI
 ```bash
 cargo run -p clawhdf5-cli -- --help
 # create, save, search, recall, stats, flush-wal, agents-md, export, snapshot subcommands
 ```
 
+### HDF5 tools (`h5rs`, crate `clawhdf5-tools`)
+```bash
+cargo run -p clawhdf5-tools -- ls -r file.h5    # also dump [--json], stat, diff, check
+bash scripts/h5rs-fuzz.sh                       # every subcommand over the CVE corpus: no panic/crash/hang
+bash scripts/h5rs-check-ok-files.sh --data      # check passes every fully-read conformance file
+```
+Its interop tests compare against h5ls/h5stat/h5dump/h5diff (Debian
+`hdf5-tools`, installed in CI); `dump` must stay byte-identical to h5dump on
+the test files.
+
 ### Python bindings
 ```bash
 cd crates/clawhdf5-py
@@ -123,4 +216,12 @@ python -c "import clawhdf5; print(clawhdf5.__version__)"
 ```
 
 ## Integration
-ZeroClaw imports this as a Cargo feature (`clawhdf5` feature flag) to persist agent memory with HNSW vector search for context retrieval.
+- **ClawBrainHub** (`clawverse/clawbrainhub` on git.redclaw.dev) is the one
+  verified consumer: `cbh-core` reads and writes `.brain` files through the
+  facade (`File`, `FileBuilder`, `AttrValue`, `Selection`), `cbh-scanner`
+  uses the facade, and `cbh-cli` uses `clawhdf5_agent::bm25::BM25Index`. It
+  depends on this repo by path (`../clawhdf5`), so it builds against whatever
+  is checked out — changes to those APIs reach it directly. Verified
+  2026-09-25 against main: builds, and its 204 tests pass.
+- OpenClaw and ZeroClaw were both described as consumers; neither integrates
+  clawhdf5 (see Key Features and `docs/openclaw.md`).

CONFORMANCE.md

@@ -0,0 +1,298 @@
+# clawhdf5 conformance report
+
+Every HDF5 file of eight public corpora (pinned by commit) is read twice — by
+clawhdf5 (`conformance/probe`, the same `clawhdf5-format` calls the facade
+makes) and by h5py/libhdf5 (`conformance/ref.py`) — and the two readings are
+compared object by object: the set of hard-linked objects, each dataset's and
+attribute's shape, and a SHA-256 of its values in a canonical encoding. The
+CVE corpus is also run through `h5dump`. Each side runs under a timeout and an
+address-space limit, so a hang, crash or runaway allocation is recorded, not
+fatal. This file is generated by `conformance/run.sh`; do not edit it by hand.
+
+## Run
+
+| | |
+|---|---|
+| date | 2026-09-26 14:18 UTC |
+| clawhdf5 commit | `73a01f1256fb9bf1b1e7601f755af9e8273cec4e` |
+| machine | `tank`: AMD Ryzen 7 7800X3D 8-Core Processor, 16 CPUs, 61 GiB, Linux 7.0.0-34-generic x86_64 |
+| command | `conformance/run.sh --no-fetch --update-baseline` |
+| rustc | rustc 1.98.1 (48a229cea 2026-09-01) |
+| reference | h5py 3.16.0, HDF5 2.0.0, numpy 2.5.3, hdf5plugin 7.1.0, Python 3.14.4 |
+| h5dump | Version 1.14.6 (CVE corpus only) |
+| limits | 20 s timeout (SIGKILL), 4096 MiB address space, per process; 16 files in parallel |
+| runtime | 23 s probing + comparing (0 s fetch/build before it) |
+
+## Results
+
+A file's class is the first that applies:
+
+- **panic / hang / crash / oom** — clawhdf5 panicked (caught per object or not), hit the timeout, died on a signal, or failed an allocation. The CI gate fails on any of these.
+- **h5py-cannot-read** — libhdf5 could not open the file (or itself crashed or hung). Nothing to compare against; most are the deliberately malformed CVE reproducers.
+- **our-error** — clawhdf5 returned an error for something h5py reads.
+- **mismatch** — both read it, but the shapes, values, object set or attribute set differ.
+- **ok** — every object h5py reads, clawhdf5 reads identically.
+
+| corpus | files | ok | our-error | mismatch | h5py-cannot-read | panic | hang | crash | oom |
+|---|---|---|---|---|---|---|---|---|---|
+| NCAS-CMS_pyfive | 33 | 32 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
+| cve_hdf5 | 147 | 100 | 6 | 9 | 32 | 0 | 0 | 0 | 0 |
+| h5py_data | 4 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
+| hdf5 | 466 | 392 | 4 | 10 | 60 | 0 | 0 | 0 | 0 |
+| netcdf-c | 20 | 20 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
+| netcdf4-python | 18 | 18 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
+| usnistgov_h5wasm | 5 | 5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
+| xarray-data | 4 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
+| **all** | **697** | **575** | **10** | **20** | **92** | **0** | **0** | **0** | **0** |
+
+2 of the 20 mismatches are a known h5py bug, not ours (see *Known not-our-bug*).
+
+Corpora (fetched by `conformance/fetch-corpus.sh` into the gitignored `conformance/.cache/`):
+
+| corpus | source | commit |
+|---|---|---|
+| hdf5 | https://github.com/HDFGroup/hdf5 | `a3cf1ea82cc7` |
+| cve_hdf5 | https://github.com/HDFGroup/cve_hdf5 | `3fd1f5ae3869` |
+| netcdf-c | https://github.com/Unidata/netcdf-c | `beb7b9585273` |
+| NCAS-CMS_pyfive | https://github.com/NCAS-CMS/pyfive | `8cf07b874913` |
+| usnistgov_h5wasm | https://github.com/usnistgov/h5wasm | `02f6336527d2` |
+| netcdf4-python | https://github.com/Unidata/netcdf4-python | `6e67576d39ae` |
+| xarray-data | https://github.com/pydata/xarray-data | `a35297e9da2c` |
+| h5py_data | https://github.com/h5py/h5py (`h5py/tests/data_files`) | `b2f0347c4200` |
+
+## Panics, hangs, crashes, out-of-memory
+
+None.
+
+## Our-error root causes
+
+Grouped by normalised error message. *files* counts files whose class this cause affects.
+
+| files | objects | error | examples |
+|---:|---:|---|---|
+| 3 | 3 | `DataSizeMismatch { expected: N, actual: N }` | `cve_hdf5/cvefiles/cve-2020-18494.h5`, `cve_hdf5/cvefiles/cve-2024-32623.h5`, `cve_hdf5/cvefiles/cve-2025-2309.h5` |
+| 2 | 2 | `ChunkedReadError("…")` | `cve_hdf5/cvefiles/cve-2025-2308.h5`, `hdf5/test/testfiles/bad_nbit_parms_walk.h5` |
+| 2 | 2 | `UnsupportedFilter(N)` | `hdf5/HDF5Examples/C/H5FLT/tfiles/h5ex_d_blosc2.h5`, `hdf5/HDF5Examples/C/H5FLT/tfiles/h5ex_d_zfp.h5` |
+| 1 | 1 | `UnexpectedEof { expected: N, available: N }` | `cve_hdf5/cvefiles/cve-2019-9151.h5` |
+| 1 | 1 | `MissingMessage(Dataspace)` | `cve_hdf5/cvefiles/cve-2024-33874.h5` |
+| 1 | 1 | `InvalidObjectHeaderVersion(N)` | `hdf5/tools/test/testfiles/h5clear_mdc_image.h5` |
+
+## Mismatch root causes
+
+| files | objects | cause | examples |
+|---:|---:|---|---|
+| 13 | 14 | `missing-object` | `cve_hdf5/cvefiles/cve-2019-8397.h5`, `cve_hdf5/cvefiles/cve-2019-8398.h5`, `cve_hdf5/cvefiles/cve-2021-46243.h5` (+10 more) |
+| 2 | 6 | `extra-attr` | `cve_hdf5/cvefiles/cve-2018-17438`, `cve_hdf5/cvefiles/cve-2018-17439` |
+| 1 | 1 | `attr-values: ours=vlen(>u8) h5py=object layout=- filters=-` | `NCAS-CMS_pyfive/tests/data/attr_datatypes.hdf5` |
+| 1 | 4 | `extra-object` | `cve_hdf5/cvefiles/cve-2021-46244.h5` |
+| 1 | 1 | `values: ours=<f4 h5py=float32 layout=chunked filters=-` | `cve_hdf5/cvefiles/cve-2025-44904.h5` |
+| 1 | 1 | `values: ours=>i2 h5py=>i2 layout=chunked filters=[6]` | `cve_hdf5/cvefiles/cve-2025-44905.h5` |
+| 1 | 1 | `values: ours=>f4 h5py=>f4 layout=chunked filters=[2]` | `cve_hdf5/cvefiles/cve-2025-44905.h5` |
+| 1 | 1 | `values: ours=<f4 h5py=float32 layout=chunked filters=[2]` | `cve_hdf5/cvefiles/cve-2025-44905.h5` |
+| 1 | 1 | `values: ours=((<i4)[6, 3])[4] h5py=(('<i4', (6, 3)), (4,)) layout=contiguous filters=-` | `hdf5/tools/test/testfiles/tarray3.h5` |
+| 1 | 1 | `values: ours=vlen({r:>f4,i:>f4}8) h5py=object layout=contiguous filters=-` | `hdf5/tools/test/testfiles/tcomplex_be.h5` |
+
+## CVE corpus: clawhdf5 vs h5dump vs h5py
+
+The 147 files of [HDFGroup/cve_hdf5](https://github.com/HDFGroup/cve_hdf5) — reproducers for
+published libhdf5 CVEs and fuzzer finds. *read* = produced output (possibly with per-object
+errors), *error* = refused cleanly. h5dump exits non-zero on any error anywhere in a file, so
+its read/error split is not comparable with the other two rows; the panic, crash, hang and oom
+columns are.
+
+| tool | read | error | panic | crash | hang | oom |
+|---|---:|---:|---:|---:|---:|---:|
+| clawhdf5 | 140 | 7 | 0 | 0 | 0 | 0 |
+| h5dump 1.14.6 | 16 | 129 | 0 | 2 | 0 | 0 |
+| h5py 3.16.0 / HDF5 2.0.0 | 115 | 31 | 0 | 1 | 0 | 0 |
+
+<details><summary>Per-file outcomes</summary>
+
+| file | h5dump | h5py | clawhdf5 | class |
+|---|---|---|---|---|
+| cvefiles/cve-2016-4330.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2016-4331.h5 | error exit | read 25 obj, 1 errors | read 25 obj, 1 errors | ok |
+| cvefiles/cve-2016-4332-mtime-new.h5 | error exit | read 25 obj, 1 errors | read 25 obj, 1 errors | ok |
+| cvefiles/cve-2016-4332-mtime.h5 | error exit | read 4 obj, 3 errors | read 4 obj, 3 errors | ok |
+| cvefiles/cve-2016-4332-stab.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2016-4333.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2017-17505.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2017-17506.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2017-17507.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2017-17508.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2017-17509.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-11202.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-11203.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-11204.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-11205.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-11206-new.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-11206-old.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-11207.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-13866.h5 | error exit | open error | open error | h5py-cannot-read |
+| cvefiles/cve-2018-13867.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2018-13868.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-13869.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2018-13870.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2018-13871.h5 | error exit | read 2 obj | read 2 obj | ok |
+| cvefiles/cve-2018-13872.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2018-13873.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2018-13874.h5 | error exit | open error | open error | h5py-cannot-read |
+| cvefiles/cve-2018-13875.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-13876.h5 | error exit | open error | open error | h5py-cannot-read |
+| cvefiles/cve-2018-14031.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-14033.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-14034.h5 | error exit | read 1 obj, 2 errors | read 1 obj | ok |
+| cvefiles/cve-2018-14035.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-14460.h5 | error exit | read 3 obj, 2 errors | read 3 obj, 2 errors | ok |
+| cvefiles/cve-2018-15671.h5 | ok | read 1 obj | read 1 obj | ok |
+| cvefiles/cve-2018-15672.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-16438.h5 | error exit | read 1 obj, 1 errors | read 1 obj | ok |
+| cvefiles/cve-2018-17233.h5 | error exit | read 6 obj, 1 errors | read 6 obj, 1 errors | ok |
+| cvefiles/cve-2018-17234.h5 | error exit | read 6 obj, 1 errors | read 6 obj, 1 errors | ok |
+| cvefiles/cve-2018-17237.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2018-17432.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-17433 | error exit | open error | open error | h5py-cannot-read |
+| cvefiles/cve-2018-17434.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-17435.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-17436 | error exit | open error | open error | h5py-cannot-read |
+| cvefiles/cve-2018-17437.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2018-17438 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | mismatch |
+| cvefiles/cve-2018-17439 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | mismatch |
+| cvefiles/cve-2019-8396.h5 | error exit | read 3 obj, 2 errors | read 3 obj, 2 errors | ok |
+| cvefiles/cve-2019-8397.h5 | error exit | read 3 obj, 2 errors | read 2 obj, 1 errors | mismatch |
+| cvefiles/cve-2019-8398.h5 | error exit | read 3 obj, 2 errors | read 2 obj, 1 errors | mismatch |
+| cvefiles/cve-2019-9151.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 2 errors | our-error |
+| cvefiles/cve-2019-9152.h5 | error exit | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2020-10809 | error exit | open error | open error | h5py-cannot-read |
+| cvefiles/cve-2020-10810.h5 | error exit | open error | read 2 obj | h5py-cannot-read |
+| cvefiles/cve-2020-10811.h5 | error exit | read 25 obj, 1 errors | read 25 obj, 1 errors | ok |
+| cvefiles/cve-2020-10812.h5 | error exit | open error | read 2 obj | h5py-cannot-read |
+| cvefiles/cve-2020-18232.h5 | error exit | read 3 obj, 2 errors | read 3 obj, 2 errors | ok |
+| cvefiles/cve-2020-18494.h5 | ok | read 2 obj | read 2 obj, 1 errors | our-error |
+| cvefiles/cve-2021-36977.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2021-37501.h5 | error exit | read 18 obj, 1 errors | read 18 obj, 1 errors | ok |
+| cvefiles/cve-2021-45829.h5 | error exit | read 1 obj, 2 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2021-45830.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2021-45833.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2021-46242.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2021-46243.h5 | error exit | read 3 obj, 2 errors | read 2 obj, 1 errors | mismatch |
+| cvefiles/cve-2021-46244.h5 | error exit | read 2 obj, 1 errors | read 6 obj, 4 errors | mismatch |
+| cvefiles/cve-2024-29157.h5 | error exit | read 4 obj, 7 errors | read 4 obj, 7 errors | ok |
+| cvefiles/cve-2024-29158.h5 | ok | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2024-29159.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2024-29160.h5 | error exit | read 4 obj, 1 errors | read 4 obj, 1 errors | ok |
+| cvefiles/cve-2024-29161.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2024-29162.h5 | error exit | read 17 obj, 4 errors | read 17 obj, 4 errors | ok |
+| cvefiles/cve-2024-29163.h5 | error exit | read 7 obj, 1 errors | read 7 obj, 1 errors | ok |
+| cvefiles/cve-2024-29164.h5 | ok | read 3 obj | read 3 obj | ok |
+| cvefiles/cve-2024-29165.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2024-29166.h5 | error exit | read 17 obj, 2 errors | read 17 obj | ok |
+| cvefiles/cve-2024-32605.h5 | ok | read 6 obj, 1 errors | read 6 obj, 1 errors | ok |
+| cvefiles/cve-2024-32606.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2024-32607-1.h5 | ok | read 10 obj | read 10 obj | ok |
+| cvefiles/cve-2024-32607-2.h5 | error exit | read 9 obj, 1 errors | read 9 obj, 1 errors | ok |
+| cvefiles/cve-2024-32608.h5 | error exit | read 6 obj, 1 errors | read 6 obj, 1 errors | ok |
+| cvefiles/cve-2024-32609.h5 | error exit | SIGSEGV | read 3 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2024-32610.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2024-32611.h5 | ok | read 6 obj | read 6 obj | ok |
+| cvefiles/cve-2024-32612.h5 | ok | read 3 obj | read 3 obj | ok |
+| cvefiles/cve-2024-32613.h5 | error exit | read 7 obj, 1 errors | read 7 obj, 1 errors | ok |
+| cvefiles/cve-2024-32614.h5 | error exit | read 25 obj, 2 errors | read 25 obj, 2 errors | ok |
+| cvefiles/cve-2024-32615.h5 | error exit | read 4 obj, 1 errors | read 4 obj, 1 errors | ok |
+| cvefiles/cve-2024-32616.h5 | error exit | read 10 obj, 7 errors | read 10 obj, 6 errors | ok |
+| cvefiles/cve-2024-32617.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2024-32618.h5 | error exit | read 4 obj, 2 errors | read 3 obj, 1 errors | mismatch |
+| cvefiles/cve-2024-32619.h5 | error exit | read 3 obj, 2 errors | read 3 obj, 2 errors | ok |
+| cvefiles/cve-2024-32620.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2024-32621.h5 | ok | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2024-32622.h5 | ok | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2024-32623.h5 | ok | read 6 obj | read 6 obj, 1 errors | our-error |
+| cvefiles/cve-2024-32624.h5 | error exit | read 6 obj, 1 errors | read 6 obj | ok |
+| cvefiles/cve-2024-33873.h5 | error exit | read 4 obj, 1 errors | read 4 obj, 1 errors | ok |
+| cvefiles/cve-2024-33874.h5 | ok | read 6 obj, 1 errors | read 6 obj, 2 errors | our-error |
+| cvefiles/cve-2024-33875.h5 | ok | read 2 obj | read 2 obj | ok |
+| cvefiles/cve-2024-33876.h5 | ok | read 3 obj, 1 errors | read 3 obj, 1 errors | ok |
+| cvefiles/cve-2024-33877.h5 | error exit | read 8 obj, 1 errors | read 8 obj, 1 errors | ok |
+| cvefiles/cve-2025-2153.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-2308.h5 | error exit | read 25 obj, 1 errors | read 25 obj, 2 errors | our-error |
+| cvefiles/cve-2025-2309.h5 | ok | read 6 obj, 1 errors | read 6 obj, 1 errors | our-error |
+| cvefiles/cve-2025-2310.h5 | error exit | read 24 obj, 8 errors | read 24 obj, 8 errors | ok |
+| cvefiles/cve-2025-2912.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-2913.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-2914.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-2915.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-2923.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-2924.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-2925.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-2926.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-44904.h5 | error exit | read 25 obj, 1 errors | read 25 obj, 1 errors | mismatch |
+| cvefiles/cve-2025-44905.h5 | error exit | read 25 obj, 3 errors | read 25 obj, 3 errors | mismatch |
+| cvefiles/cve-2025-6269-1.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-6269-2.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-6269-3.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-6269-4.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-6270-1.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-6270-2.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-6270-3.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-6516.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-6750.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-6816.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-6817.h5 | error exit | open error | read 1 obj | h5py-cannot-read |
+| cvefiles/cve-2025-6818.h5 | error exit | open error | read 1 obj | h5py-cannot-read |
+| cvefiles/cve-2025-6856.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-6857.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-6858.h5 | SIGSEGV | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-7067.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2025-7068.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2025-7069.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| cvefiles/cve-2026-26200.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| cvefiles/cve-2026-34734.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/cve-2026-92627.h5 | error exit | read 2 obj, 1 errors | read 2 obj, 1 errors | ok |
+| cvefiles/unknown-1.h5 | error exit | read 11 obj, 1 errors | read 11 obj, 1 errors | ok |
+| fuzzerfiles/gh-4431-poc-03.h5 | error exit | read 1 obj | read 1 obj | ok |
+| fuzzerfiles/gh-4432-poc-05.h5 | SIGSEGV | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| fuzzerfiles/gh-4433-poc-08.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| fuzzerfiles/gh-4434-poc-09.h5 | error exit | open error | read 1 obj, 1 errors | h5py-cannot-read |
+| fuzzerfiles/gh-4435-poc-10.h5 | error exit | read 1 obj, 1 errors | read 1 obj, 1 errors | ok |
+| fuzzerfiles/gh-4585.h5 | error exit | open error | open error | h5py-cannot-read |
+| fuzzerfiles/gh_2649_flawed.h5 | error exit | read 9 obj, 1 errors | read 9 obj, 1 errors | ok |
+| fuzzerfiles/gh_2649_plain_model.h5 | ok | read 10 obj | read 10 obj | ok |
+
+</details>
+
+## Known not-our-bug
+
+- **h5py big-endian variable-length sequences.** h5py returns the elements of a VL sequence
+  whose base type is big-endian with the file's big-endian bytes but a native (little-endian)
+  numpy dtype, so the values it reports are byte-swapped garbage; `h5dump` prints the values
+  clawhdf5 reads. Reproducer: `h5py.vlen_dtype(np.dtype('>f4'))` dataset holding `[1.0, 2.0]`
+  reads back in h5py as `[4.6e-41, 9.0e-44]`. Affected here: `NCAS-CMS_pyfive/tests/data/attr_datatypes.hdf5`, `hdf5/tools/test/testfiles/tcomplex_be.h5`.
+- **Non-IEEE floats and partial-precision integers (N-Bit).** libhdf5 converts a float whose
+  bit layout is not IEEE (e.g. `H5Tset_precision` for the N-Bit filter) or an integer with a
+  bit offset / reduced precision into the plain numpy type of the same size. The probe
+  compares such values as converted numbers, not raw file bytes (before 2026-09-25 it compared
+  raw bytes, which reported every N-Bit float dataset as a mismatch).
+- **Types h5py widens.** Where h5py reads a type into a numpy type of a different size
+  (FP8 -> float16, bfloat16 -> float32, x87 long double -> float128) the values are not
+  compared (shape and presence still are): dataset file type size 1 -> numpy float16 (2) (15x), attr file type size 1 -> numpy float16 (2) (15x), dataset file type size 2 -> numpy float32 (4) (2x), dataset file type size 8 -> numpy float128 (16) (1x), dataset file type size 12 -> numpy float128 (16) (1x), attr file type size 2 -> numpy float32 (4) (1x), dataset file type size 2 -> numpy >f4 (4) (1x), attr file type size 2 -> numpy >f4 (4) (1x).
+- **References** are compared by presence only (`R`), not by target.
+
+## Objects h5py fails on but clawhdf5 reads
+
+- 19 x `OSError: Can't synchronously read data (no appropriate function for conversion path)`
+- 1 x `TypeError: unhandled dtype kind M (dtype('…'))`
+- 1 x `TypeError: No NumPy equivalent for TypeTimeID exists`
+- 1 x `KeyError: "…"`
+- 1 x `ValueError: Insufficient precision in available types to represent (N, N, N, N, N)`
+
+## Reproduce
+
+```sh
+# needs: Rust, python3 with h5py numpy hdf5plugin (conformance/requirements.txt), h5dump (hdf5-tools), git
+CLAWHDF5_PYTHON=/path/to/venv/bin/python conformance/run.sh
+```
+
+The corpus (about 450 MB of sparse checkouts) is cached in `conformance/.cache/`; results for
+every file, both sides' raw JSON and stderr, are in `conformance/.cache/results/`.
+`conformance/baseline.json` holds the ok files the nightly CI job (`.gitea/workflows/conformance.yml`)
+must keep; `conformance/run.sh --update-baseline` rewrites it.

Cargo.toml

@@ -16,13 +16,18 @@ members = [
     "crates/clawhdf5-cli",
     "crates/clawhdf5-napi",
     "crates/clawhdf5-bench",
+    "crates/clawhdf5-tools",
+    "crates/clawhdf5-wasm",
     "crates/libaec-sys",
 ]
 resolver = "2"
 
 [workspace.package]
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+# Oldest toolchain that builds the whole workspace; CI checks it. wgpu (in
+# clawhdf5-gpu) requires 1.92.
+rust-version = "1.92"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
 
@@ -31,3 +36,12 @@ tempfile = "3"
 criterion = { version = "0.5", features = ["html_reports"] }
 half = "2.7"
 serde = { version = "1", features = ["derive"] }
+
+# The browser build of clawhdf5-wasm (examples/wasm-viewer/build.sh): size
+# over speed, whole-program optimisation. Native profiles are unaffected.
+[profile.wasm-release]
+inherits = "release"
+opt-level = "s"
+lto = true
+codegen-units = 1
+panic = "abort"

README.md

@@ -3,24 +3,103 @@
 **The memory layer AI agents deserve. One file. Pure Rust. Zero C dependencies.**
 
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
-[![Rust](https://img.shields.io/badge/rust-1.75%2B-orange.svg)](https://www.rust-lang.org)
-[![Tests](https://img.shields.io/badge/tests-1650%2B%20passing-brightgreen.svg)](#performance)
-[![LongMemEval](https://img.shields.io/badge/LongMemEval%20oracle-Turn--Level%20Hit@5%2084%25%20BM25--only-blue.svg)](BENCHMARKS.md#longmemeval-results)
-[![Footprint](https://img.shields.io/badge/footprint-6.5%20KB%2Frecord-lightgrey.svg)](BENCHMARKS.md#memory-footprint)
+[![Rust](https://img.shields.io/badge/rust-1.92%2B-orange.svg)](https://www.rust-lang.org)
+[![Tests](https://img.shields.io/badge/tests-1850%2B-brightgreen.svg)](#building)
+[![LongMemEval](https://img.shields.io/badge/LongMemEval__s-Turn--Level%20Hit@5%2081.4%25%20hybrid-blue.svg)](BENCHMARKS.md#longmemeval-results)
+[![Footprint](https://img.shields.io/badge/on--disk-~820%20B%2Frecord%20float16%2C%20synthetic%20text-lightgrey.svg)](BENCHMARKS.md#memory-footprint-1)
 
-ClawHDF5 is a pure-Rust HDF5 implementation combined with a research-grade agent memory engine. It gives AI agents persistent, searchable, cryptographically verifiable memory — all stored in a single portable file.
+ClawHDF5 is a pure-Rust HDF5 implementation combined with a research-grade agent memory engine. It gives AI agents persistent, searchable, cryptographically verifiable memory (Ed25519-signed checkpoints) — all stored in a single portable file.
 
 > **Two things live here:**
 > - **A general-purpose, pure-Rust HDF5 library** — zero C dependencies, NetCDF-4 support, SIMD/GPU acceleration. See the **[Crate Map](#crate-map)** and **[BENCHMARKS.md](BENCHMARKS.md)** for the libhdf5 head-to-head numbers.
 > - **An agent memory layer built on top of it** — vector search, knowledge graph, hippocampal-style consolidation, in `clawhdf5-agent`.
 
-```
-cargo add clawhdf5                          # core HDF5 read/write, no agent layer
-cargo add clawhdf5-agent --features agent   # + agent memory layer
+The crates are not on crates.io yet, so depend on them from git:
+
+```toml
+[dependencies]
+clawhdf5       = { git = "https://git.redclaw.dev/quantumclaw/clawhdf5" }  # core HDF5 read/write
+clawhdf5-agent = { git = "https://git.redclaw.dev/quantumclaw/clawhdf5" }  # + agent memory layer
 ```
 
+> **C dependencies, precisely:** the core crates (`clawhdf5`, `clawhdf5-agent`,
+> `-format`, `-io`, `-filters`, `-ann`, `-accel`, `-netcdf4`, `-cli`) build no C
+> code by default — no libhdf5, and deflate is the pure-Rust
+> [zlib-rs](https://github.com/trifectatechfoundation/zlib-rs), which matches
+> zlib-ng on HDF5 reads and writes and produces byte-identical output
+> ([BENCHMARKS.md § Deflate backend](BENCHMARKS.md#deflate-backend-zlib-rs-vs-zlib-ng)).
+> CI fails if a C-building crate enters their default dependency tree. C comes
+> in only when you ask for it: `fast-deflate` (zlib-ng, needs cmake), `zstd`,
+> `szip`, the BLAS backends, `clawhdf5-migrate` (bundled SQLite) and the
+> Node.js bindings.
+
 > **New here?** Start with the **[Quickstart Guide](docs/QUICKSTART.md)** · See **[Use Cases](docs/USE_CASES.md)** · Read **[Benchmarks](BENCHMARKS.md)**
 
+## What's new (v2.2 → v2.7, and unreleased)
+
+Five releases in September 2026. Details, including upgrade notes and every
+breaking change, are in [CHANGELOG.md](CHANGELOG.md).
+
+**HDF5 correctness (read these if you read files with an earlier release)**
+- **Extensible Array chunk indexes returned wrong data** past the 36th chunk —
+  any dataset with one unlimited dimension. Silent: plausible numbers from the
+  wrong chunks. Fixed in v2.7.0; re-read affected data.
+- Fixed and Extensible Array checksums are now verified, so a corrupt chunk
+  index is `ChecksumMismatch` instead of wrong data (v2.7.0).
+- Compound datatypes written with default libver bounds (plain
+  `h5py.File(path, 'w')`) were mis-parsed; HDF5 2.0 compound v5 and native
+  complex (class 11) types now parse (v2.2.0–v2.3.0).
+- Committed datatypes, fill values, soft links and `H5T_STD_REF` references now
+  read correctly; external links and external raw data are explicit errors;
+  `attrs()` no longer silently drops attributes (v2.3.0–v2.5.0).
+- Datasets indexed by a version-2 B-tree now read (v2.5.0).
+
+**Security and robustness**
+- A crafted file could abort any reader via B-tree v2 recursion or explode it
+  via shared children; both are now fast errors (v2.7.0).
+- Virtual-dataset source paths are confined to the file's directory; chunked
+  reads use overflow-checked sizes and fallible allocation, and the facade
+  writes files atomically (v2.3.0).
+- Agent store: single-writer lock plus `open_read_only`; a crash between
+  checkpoint and WAL truncate no longer duplicates entries; unreadable WALs are
+  quarantined instead of blocking `open()` (v2.3.0).
+
+**Search quality and speed**
+- HNSW neighbour selection now uses the paper's diversity heuristic: recall@10
+  at 100K went from 0.31 to 0.98 (v2.4.0).
+- `hybrid_search` is 79–190× faster than v2.3.0 (p50 0.07 ms at 1K, 4.65 ms at
+  100K). It no longer rebuilds BM25 or rewrites the store per query, and the
+  HNSW graph is persisted (v2.4.0).
+- Default fusion weights are now the measured 0.4 / 0.6 (v2.5.0). Re-ranking had
+  been discarding the retrieval score, costing the Markdown backend 40.6pp of
+  Hit@1; fixed in v2.6.0.
+- Selection reads whose bounding box covers at most half the dataset decode
+  only the chunks they touch (a 64×64 window: 105 ms to 0.39 ms), and full
+  reads are 1.2–1.9× faster (v2.5.0).
+
+**Memory**
+- A loaded store holds ~30% less (embeddings stored once, v2.6.0), and the
+  int8 HNSW index, **on by default for new stores** (unreleased), brings a
+  100K × 384 store to 1.74× the raw vectors. At equal recall it is also faster
+  than `f32`: 1.63× QPS on AVX2, 1.18× on a Raspberry Pi 5 (NEON `SDOT`).
+
+**Interop and search (unreleased)**
+- **Files we write now open in h5py and libhdf5.** Every `f32` dataset —
+  including every agent store's embeddings — and every empty dataset was
+  refused by libhdf5. Both were write-side bugs in every release; agent stores
+  fix themselves at their next checkpoint. See
+  [docs/known-issues.md](docs/known-issues.md).
+- `MemoryConfig::float16` now stores half-precision embeddings (it was
+  ignored), and is on by default for new stores: 48% smaller files, and
+  identical LongMemEval retrieval on real embeddings.
+- `HDF5Memory::search` with `SearchOptions`: filter by source channel (exact
+  filtered top-k, never slower than unfiltered), and opt-in re-ranking and
+  confidence rejection, which used to be reachable only through `ClawhdfBackend`.
+
+**Tooling**
+- CI now runs the h5py/netCDF4 interop suites for real (they had been skipping
+  silently) and runs an aarch64 job for the NEON kernels.
+
 ---
 
 ## Why ClawhDF5?
@@ -33,16 +112,16 @@ Every AI agent needs memory. Today that means scattered Markdown files, SQLite d
 | Keyword search | Separate FTS engine | Integrated BM25 |
 | Knowledge graph | Neo4j or none | In-file graph with spreading activation |
 | Memory consolidation | Manual pruning | Hippocampal-inspired automatic tiers |
-| Temporal queries | Custom code | Native temporal index (716ns) |
-| Multi-modal | Multiple stores | Unified cross-modal search |
-| Security | Hope for the best | Provenance tracking + anomaly detection |
+| Temporal queries | Custom code | Native temporal index (622 ns range query over 10K) |
+| Multi-modal | Multiple stores | Unified cross-modal search (exact scan: 842 µs over 1K records) |
+| Integrity | Hope for the best | Ed25519-signed checkpoints that pinpoint any edited record, chained-CRC WAL, checksummed chunk indexes, write-anomaly alerts |
 | Portability | Config + DB + files | **One `.h5` file. Copy it anywhere.** |
 
 ---
 
 ## Performance
 
-Vector search and agent-memory operations below are benchmarked on Intel i7-12650H (10C/16T), 384-dim embeddings, Criterion.rs. The HDF5 Core I/O table immediately below is from a separate, independently reproduced run (see its own hardware note).
+The brute-force/IVF vector search, agent-memory, on-disk footprint and consolidation figures below were measured 2026-09-24 on tank (AMD Ryzen 7 7800X3D, 8C/16T), commit 5c8323c, 384-dim embeddings; the commands are in [BENCHMARKS.md](BENCHMARKS.md). Exceptions are marked where they appear: the HDF5 Core I/O table immediately below is from a separate, independently reproduced run (see its own hardware note), and the HNSW `f32`/`i8` table and the in-memory `i8` column were not re-measured on 2026-09-24.
 
 ### HDF5 Core I/O (vs libhdf5 1.14.6)
 
@@ -58,31 +137,63 @@ Figures below are from an independent reproduction run on a second machine (AMD
 | Sequential read (100K f32) | 23.3 µs | 63.6 µs | **2.7×** |
 | Sequential write (100K f32) | 210 µs | 189 µs | **≈ tie** |
 
+The chunked-write row was re-measured on the same machine on 2026-09-23, after
+the default deflate backend became pure-Rust zlib-rs: 1.46 ms against
+libhdf5's 51.4 ms (**35×**), and 1.48 ms with zlib-ng. libhdf5's own time on
+that machine moved from 65.0 to 51.4 ms between the two dates, which is most
+of the difference from 45×; compare same-day numbers only.
+
 ### Vector Search
 
-| Scale | Flat | IVF (nprobe=10) | IVF-PQ | vs MemX¹ |
-|-------|------|-----------------|--------|----------|
-| 1K | **54 µs** | — | — | — |
-| 10K | 753 µs | **27 µs** | — | — |
-| 100K | 11.4 ms | 1.32 ms | **1.19 ms** | ~8–76× (see caveat) |
+**HNSW (the default backend for `hybrid_search`)** — `search_harness`, clustered
+384-dim data, M = 16, ef_construction = 64, recall measured against an exact scan.
+See [BENCHMARKS.md § Search harness](BENCHMARKS.md#search-harness-baseline-v230)
+and [§ Quantising the index copy](BENCHMARKS.md#quantising-the-index-copy-quantized_index):
 
-> Reproduced on the same second machine (Ryzen 7 7800X3D) with a corrected,
-> apples-to-apples SIMD/scalar/parallel comparison methodology — see
-> [BENCHMARKS.md § Independent Validation: tank — LongMemEval & Vector
-> Search](BENCHMARKS.md#independent-validation-tank--longmemeval--vector-search-ryzen-7-7800x3d-2026-08-05).
+| N = 100K, ef = 64 | recall@10 | QPS | build |
+|---|---:|---:|---:|
+| `f32` index | 0.9945 | 13 399 | 3.2 s |
+| `i8` index + exact re-score (**default for new stores**) | 0.9940 | **21 848** | **1.8 s** |
+
+Before the v2.4.0 neighbour-selection fix, recall@10 at 100K was 0.31. These
+two rows are a paired comparison (medians of alternating runs, same binary).
+A single `f32` run on 2026-09-24 measured recall 0.9945, 19 001 QPS and a
+2.7 s build; the int8 row was not re-run, so the pair has not been re-checked
+([§ Quantising the index copy](BENCHMARKS.md#quantising-the-index-copy-quantized_index)).
+
+**Brute-force and IVF paths** (Criterion, tank, 2026-09-24):
+
+| Scale | Flat | IVF (nprobe=10) | IVF-PQ | MemX¹ (claimed, end-to-end) |
+|-------|------|-----------------|--------|----------|
+| 1K | **47.4 µs** | — | — | — |
+| 10K | 500.5 µs | **24.8 µs** | — | — |
+| 100K | 6.58 ms | 592 µs | **869 µs** | <90 ms |
+
+> These replace figures from the original i7-12650H run (flat 54 µs / 753 µs /
+> 11.4 ms); a 2026-08-05 run on tank had already matched the new ones — see
+> [BENCHMARKS.md § Vector Search Latency](BENCHMARKS.md#vector-search-latency).
 
 ### Agent Memory Operations
 
 | Operation | Latency | Scale |
 |-----------|---------|-------|
-| Hybrid search (RRF) | **222 µs** | 1K records |
-| BM25 keyword search | **67 µs** | 1K records |
-| Knowledge graph BFS | **24 µs** | 1K entities |
-| Spreading activation | **17 µs** | 100 entities |
-| Temporal range query | **716 ns** | 10K timestamps |
-| Consolidation cycle | **164 µs** | 1K records |
-| Memory write (WAL) | **18 µs** | per record (group-commit append; HDF5 batched at flush) |
-| Importance gate | **61 ns** | per record |
+| Hybrid search (`HDF5Memory::hybrid_search`, p50) | **0.07 ms** / 0.49 ms / 4.69 ms | 1K / 10K / 100K records |
+| BM25 keyword search | **20.4 µs** | 1K records |
+| Knowledge graph BFS | **23.1 µs** | 1K entities |
+| Spreading activation | **10.1 µs** | 100 entities |
+| Temporal range query | **622 ns** | 10K timestamps |
+| Consolidation cycle | **115.2 µs** | 1K records |
+| Cross-modal search (exact scan, 2 embeddings per record) | **842.0 µs** / 8.44 ms | 1K / 10K records |
+| Memory write (WAL) | **26.1 µs** | per record (group-commit append; HDF5 batched at flush) |
+| Importance gate | **57.6 ns** | per record (trivial skip) |
+
+The old 18 µs WAL write was undated, from another machine: v2.3.0 measures
+24.3 µs on the same hardware as this table, the same as an `f32` store today.
+`float16` stores (the new default) add ~2 µs for rounding; the int8 index adds
+nothing. See [BENCHMARKS.md § Write Path](BENCHMARKS.md#write-path).
+Knowledge-graph traversal was briefly 6.5x slower (155 µs) until this re-run
+found and fixed an adjacency index rebuilt on every traversal; see
+[§ Knowledge Graph](BENCHMARKS.md#knowledge-graph).
 
 ### Chunked Write Throughput (codec comparison)
 
@@ -97,7 +208,7 @@ by default (AoS→SoA byte transpose, +157–204% throughput for float data):
 
 Use `.with_zstd(3)` or `.with_deflate(6)` for write-heavy workloads — both now perform at ~720–750 MiB/s on large matrices. Use `.with_pcodec()` for write-once/read-many workloads where compression ratio matters more than encode speed. Disable auto-shuffle with `.without_shuffle()` for byte arrays that don't benefit from AoS→SoA transposition.
 
-> ¹ MemX ([arxiv:2603.16171](https://arxiv.org/abs/2603.16171), March 2026): Rust + libSQL, claims <90ms at 100K records. **Not like-for-like:** MemX's figure is *end-to-end* (embeddings + FTS5 + four-factor re-ranking); ours is a *single component* (raw vector search). The ratio overstates the real advantage by an unquantified margin — order-of-magnitude indication only. See [BENCHMARKS.md](BENCHMARKS.md#comparison-to-memx-arxiv260316171).
+> ¹ MemX ([arxiv:2603.16171](https://arxiv.org/abs/2603.16171), March 2026): Rust + libSQL, claims <90ms at 100K records. **Not like-for-like:** MemX's figure is *end-to-end* (embeddings + FTS5 + four-factor re-ranking); ours is a *single component* (raw vector search), so the two columns are not comparable and no ratio is given. See [BENCHMARKS.md](BENCHMARKS.md#comparison-to-memx-arxiv260316171).
 
 ### LongMemEval Retrieval Recall
 
@@ -115,13 +226,17 @@ declaration:
 
 Hybrid is the strongest configuration, which is what running two retrieval stages
 is for. The weights matter more than the stages: a sweep of `vector_weight` from
-0.0 to 1.0 found the long-standing `0.7/0.3` default is **strictly dominated** by
-`0.4/0.6` — better on Hit@1, Hit@5, Hit@10 and MRR at both granularities. Use
-`0.4/0.6`, or `0.3/0.7` if rank-1 precision matters most. See
-[BENCHMARKS.md § Weight sweep](BENCHMARKS.md#longmemeval-results).
+0.0 to 1.0 found the old `0.7/0.3` default is **strictly dominated** by
+`0.4/0.6` — better on Hit@1, Hit@5, Hit@10 and MRR at both granularities. Since
+v2.5.0 `0.4/0.6` is the default (`hybrid::DEFAULT_FUSION`, used by
+`unified_search`, `hybrid_search_with` and `ClawhdfBackend`); callers that
+pass weights to `hybrid_search` explicitly choose their own. Use `0.3/0.7` if
+rank-1 precision matters most. Reciprocal rank fusion is selectable
+(`hybrid::Fusion::Rrf`) but measured worse than the weighted sum. See
+[BENCHMARKS.md § Weight sweep](BENCHMARKS.md#weight-sweep--full-haystack-n500).
 
-Vector embeddings require `--features embeddings`; without it the vector stage is
-inert and only the BM25 row is produced, which is what every previously published
+The benchmark's vector stage requires `clawhdf5-bench`'s `embeddings` feature
+(real MiniLM embeddings); without it the vector stage is inert and only the BM25 row is produced, which is what every previously published
 number here measured.
 
 On the easier `longmemeval_oracle` variant (evidence sessions only) the same
@@ -146,19 +261,53 @@ retrieval recall reported as QA accuracy typically overstates by 20–30 points.
 
 ### Memory Footprint
 
-| Records | File Size | Bytes/Record | With Compression |
-|---------|-----------|--------------|------------------|
-| 1K | ~6.5 MB | ~6.5 KB | ~2.1 MB (3.1x) |
-| 10K | ~65 MB | ~6.5 KB | ~21 MB (3.1x) |
-| 100K | ~645 MB | ~6.5 KB | ~208 MB (3.1x) |
+**On disk** — 384-dim `float16` embeddings (the default for new stores),
+200-char text, `footprint_bench`
+([BENCHMARKS.md § Memory Footprint](BENCHMARKS.md#memory-footprint-1)):
+
+| Records | File Size | Bytes/Record | Gzip-6 compressed |
+|---------|-----------|--------------|-------------------|
+| 1K | 810.4 KB | 829 B | 56.4 KB |
+| 10K | 7.8 MB | 820 B | 471.3 KB |
+| 100K | 76.7 MB | 803 B | 4.5 MB |
+
+The benchmark's synthetic embeddings and text are far more repetitive than
+real data (only 40 distinct texts), so no column here is an expectation for
+real data. The compressed column is an upper bound, and the Bytes/Record
+column is optimistic too: it is not an uncompressed figure, because the store
+always deflates its text (any string dataset of 4 KiB or more) whatever
+`MemoryConfig::compression` says. The `float16` embeddings alone are 768 B per
+record, so 200 characters of real text would take a record above 820 B.
+This table used to show `f32` stores (1.7 KB per record, 169.8 MB at 100K);
+those were not re-measured. The float16 study compares the two on the same
+data: 100K × 384 records take 80.8 MiB as `float16` and 154.0 MiB as `f32`.
+
+**In memory** — a store reopened from disk, 384-dim `f32`, measured with a
+counting allocator ([BENCHMARKS.md § Memory footprint](BENCHMARKS.md#memory-footprint)):
+
+| Records | Raw vectors | Reopened, `f32` index | Reopened, `i8` index (default) |
+|---------|-------------|-----------------------|--------------------------------|
+| 1K | 1 MiB | 4 MiB (2.40x) | 2 MiB (1.64x) |
+| 10K | 15 MiB | 44 MiB (3.03x) | 27 MiB (1.81x) |
+| 100K | 146 MiB | 399 MiB (2.72x) | **256 MiB (1.74x)** |
+
+Down from 505 MiB (3.44x) at 100K before v2.6.0, when the cache held every
+embedding twice. The `f32` column was re-measured on 2026-09-24 and reproduced
+exactly; the `i8` column was not re-run.
 
 ### Consolidation Efficiency
 
+1,000 records (10 signal + 990 noise), `working_capacity = 100`
+([BENCHMARKS.md § Consolidation Efficiency](BENCHMARKS.md#consolidation-efficiency)):
+
 | Metric | Before | After | Delta |
 |--------|--------|-------|-------|
-| Records in store | 1,000 | ~110 | −89% |
-| Hit@1 recall | ~60% | ~90% | +30% |
-| Search latency | ~2.8 ms | ~0.3 ms | **9x faster** |
+| Records in store | 1,000 | 100 | −90% |
+| Hit@1 recall (signal records) | 100% | 100% | no loss |
+| Search latency (avg) | 2.22 ms | 0.24 ms | **9.3x faster** |
+
+The consolidation cycle that does this took 0.13 ms; a cycle over 10K records
+takes 2.81 ms and over 100K 46.7 ms.
 
 **Full benchmark details: [BENCHMARKS.md](BENCHMARKS.md)**
 
@@ -166,74 +315,74 @@ retrieval recall reported as QA accuracy typically overstates by 20–30 points.
 
 ## Agent Memory Architecture
 
-ClawhDF5's agent memory engine implements research from 15+ recent papers on agentic memory systems. It's not a toy — it's the real thing.
+ClawhDF5's agent memory engine draws on 15+ recent papers on agentic memory systems (see [Research Foundation](#research-foundation)).
 
 ```
                          ┌─────────────────┐
                          │   Agent Query   │
                          └────────┬────────┘
                                   │
-                    ┌────────────▼────────────┐
-                    │   Hybrid Retrieval      │
-                    │  Vector + BM25 + RRF    │
-                    └────────────┬────────────┘
-                                 │
-              ┌──────────────────▼──────────────────┐
-              │         Multi-Factor Re-Ranking      │
-              │  temporal · authority · activation    │
-              └──────────────────┬──────────────────┘
-                                 │
-                    ┌────────────▼────────────┐
-                    │  Confidence Rejection   │
+                ┌─────────────────▼──────────────────┐
+                │ HDF5Memory::search                 │
+                │ optional source-channel filter     │
+                │ HNSW vector + BM25 keyword         │
+                │ weighted fusion (0.4 / 0.6)        │
+                │ × √(Hebbian activation)            │
+                └─────────────────┬──────────────────┘
+                                  │  opt-in (SearchOptions);
+                                  │  ClawhdfBackend turns both on
+                ┌─────────────────▼──────────────────┐
+                │ Multi-factor re-ranking            │
+                │ relevance · recency · authority ·  │
+                │ activation                         │
+                ├────────────────────────────────────┤
+                │ Confidence rejection               │
                 │ (suppress bad matches)             │
-                    └────────────┬────────────┘
+                └─────────────────┬──────────────────┘
                                   │
-        ┌────────────────────────▼────────────────────────┐
-        │              Memory Store (HDF5)                │
-        │                                                 │
-        │  ┌───────────┐ ┌───────────┐ ┌───────────────┐  │
-        │  │ Working   │→│ Episodic  │→│  Semantic     │  │
-        │  │ (bounded) │ │ (bounded) │ │ (long-term)   │  │
-        │  └───────────┘ └───────────┘ └───────────────┘  │
-        │                                                 │
-        │  ┌──────────┐ ┌──────────┐ ┌────────────────┐   │
-        │  │Knowledge │ │Temporal  │ │  Multi-Modal   │   │
-        │  │  Graph   │ │  Index   │ │  Embeddings    │   │
-        │  └──────────┘ └──────────┘ └────────────────┘   │
-        │                                                 │
-        │  ┌──────────┐ ┌──────────┐ ┌────────────────┐   │
-        │  │Provenance│ │ Anomaly  │ │   Source       │   │
-        │  │ Tracking │ │Detection │ │  Isolation     │   │
-        │  └──────────┘ └──────────┘ └────────────────┘   │
-        └─────────────────────────────────────────────────┘
-                              │
-                     ┌────────┴────────┐
-                     │ agent_memory.h5 │
-                     │   single file   │
-                     └─────────────────┘
+     ┌────────────────────────────▼────────────────────────────┐
+     │ In memory                                               │
+     │  cache (flat f32 embeddings) · BM25 index · HNSW index  │
+     │  provenance ledger + anomaly alerts (session-scoped)    │
+     └────────────────────────────┬────────────────────────────┘
+                                  │ WAL append; checkpoint
+     ┌────────────────────────────▼────────────────────────────┐
+     │ agent_memory.h5   /meta · /memory · /sessions ·         │
+     │                   /knowledge_graph                      │
+     │ agent_memory.h5.wal   chained-CRC write-ahead log       │
+     │ agent_memory.h5.ann   HNSW graph (derived, rebuildable) │
+     │ agent_memory.h5.lock  single-writer lock                │
+     └─────────────────────────────────────────────────────────┘
 ```
 
+Consolidation tiers (Working → Episodic → Semantic), the knowledge-graph
+algorithms, temporal and multi-modal indexes are library components you drive
+directly; the store persists the records, sessions and graph they work over.
+
 ### Module Overview
 
 | Module | What It Does |
 |--------|-------------|
-| **`knowledge`** | Entity/relation graph with BFS traversal, spreading activation, fuzzy entity resolution |
-| **`consolidation`** | Three-tier memory (Working → Episodic → Semantic) with importance scoring and time-decay |
-| **`hybrid`** | Vector + BM25 fusion with Reciprocal Rank Fusion (RRF, k=60). The vector stage uses the HNSW index by default (`hnsw` feature, on by default); disable with `--no-default-features --features float16` for an exact linear scan |
-| **`reranker`** | Multi-factor re-ranking: temporal recency, source authority, activation weight |
-| **`confidence`** | Low-confidence rejection — suppresses spurious recalls when nothing matches |
+| **`knowledge`** | Entity/relation graph with BFS traversal, spreading activation, fuzzy (Levenshtein) entity resolution |
+| **`consolidation`** | Three-tier memory (Working → Episodic → Semantic) with importance scoring, novelty, and time-decay |
+| **`hybrid`** | Vector + BM25 fusion. Default is a min-max-normalised weighted sum, vector 0.4 / keyword 0.6 (`hybrid::DEFAULT_FUSION`, tuned on LongMemEval); RRF is available via `Fusion::Rrf` / `hybrid_search_with`. The vector stage uses the HNSW index by default (`hnsw` feature); disable with `--no-default-features --features float16` for an exact linear scan |
+| **`reranker`** | Multi-factor re-ranking: retrieval relevance (leads, weight 1.0), temporal recency, source authority, activation weight. Opt-in via `SearchOptions::with_rerank`; on in `ClawhdfBackend` |
+| **`confidence`** | Low-confidence rejection — suppresses spurious recalls when nothing matches. Opt-in via `SearchOptions::with_confidence`; on in `ClawhdfBackend` |
 | **`temporal`** | Sorted timestamp index, session DAG, entity timeline, temporal query hints |
 | **`multimodal`** | Cross-modal search across text/image/audio/video embeddings |
-| **`provenance`** | Source attribution, FNV-1a content hashing, integrity verification |
-| **`anomaly`** | Write rate limiting, 15 injection pattern detectors, source distribution analysis |
-| **`openclaw`** | OpenClaw integration: MemoryBackend trait, Markdown ↔ HDF5 conversion |
+| **`signing`** | Ed25519-signed checkpoints: SHA-256 per record in a Merkle tree, plus hashes of settings, sessions and the knowledge graph; `HDF5Memory::verify` names any edited record |
+| **`provenance`** | Source attribution and an unkeyed FNV-1a content hash per record, held in memory for the session, for detecting accidental corruption (not tamper-proof) |
+| **`anomaly`** | Write rate limiting, 15 injection-pattern detectors, source-distribution analysis. Alerts never block a save; drain them with `take_anomaly_alerts` |
+| **`openclaw`** | `ClawhdfBackend`: a Markdown-oriented backend (ingest by section, search, read back by path, export). Named for OpenClaw, but **not an OpenClaw plugin** — see [docs/openclaw.md](docs/openclaw.md) |
 | **`vector_search`** | Flat cosine, pre-normed, SIMD, BLAS, GPU, parallel search paths |
-| **`ivf` / `pq`** | IVF-PQ approximate nearest neighbor for billion-scale search |
-| **`bm25`** | BM25 keyword index with TF-IDF scoring |
+| **`ivf` / `pq`** | Standalone IVF and IVF-PQ indexes (benchmarked to 100K vectors); not used by `HDF5Memory`, whose ANN index is HNSW |
+| **`bm25`** | Incremental Okapi BM25 inverted index, kept for the life of the store; optional stemming |
+| **`query_expand`** | Synonym / acronym / temporal query expansion |
 | **`entity_extract`** | Rule-based entity extraction from text chunks into the knowledge graph |
-| **`wal`** | Write-ahead log for crash-safe persistence; each entry is CRC32-checked on replay, so a corrupted entry stops replay there instead of loading bad data |
+| **`wal`** | Write-ahead log (v4) with a chained CRC32 per entry, so a corrupted, reordered, duplicated or spliced entry stops replay; checkpoints record a WAL mark so nothing is applied twice. Appends are not fsynced |
 | **`memory_strategy`** | Pluggable strategies: save-every, semantic-shift, user-correction detection |
 | **`decision_gate`** | Sub-microsecond trivial/substantive classification |
+| **`ephemeral`** | In-memory TTL/LFU working tier |
 | **`async_memory`** | Tokio-based async wrapper over the memory store (`async` feature) |
 
 ---
@@ -259,13 +408,86 @@ let values = ds.read_f64()?;
 assert_eq!(values, vec![22.5, 23.1, 21.8]);
 ```
 
+### Groups and links
+
+```rust
+use clawhdf5::{AttrValue, FileBuilder};
+
+let mut b = FileBuilder::new();
+// A path creates its missing intermediate groups, as in h5py.
+b.create_dataset("run/2026/temps").with_f64_data(&[22.5, 23.1]);
+// Builders nest; a group added at an existing path is merged into it.
+let mut run = b.create_group("run");
+run.set_attr("operator", AttrValue::String("ana".into()));
+let mut cal = run.create_group("calibration");
+cal.track_order(true); // h5py lists members in insertion order
+cal.create_dataset("offset").with_f64_data(&[0.1]);
+run.add_group(cal.finish());
+b.add_group(run.finish());
+b.add_soft_link("latest", "/run/2026");    // h5py.SoftLink
+b.add_hard_link("temps", "/run/2026/temps"); // f["temps"] = f["run/2026/temps"]
+b.add_external_link("raw", "raw.h5", "/data");
+b.write("groups.h5")?;
+```
+
+A group holds at most 65 535 links; more is an error, as is a link over
+65 515 bytes (a very long soft-link target) in a group of more than 8 links.
+
+### Python
+
+`crates/clawhdf5-py` is a Python package (PyO3 + numpy) that reads HDF5 with
+an h5py-shaped API and no libhdf5. It is not on PyPI; build it with
+[maturin](https://www.maturin.rs) into a virtualenv:
+
+```bash
+python -m venv .venv && . .venv/bin/activate
+pip install maturin numpy
+maturin develop --release -m crates/clawhdf5-py/Cargo.toml
+python -c "import clawhdf5; print(clawhdf5.__version__)"
+```
+
+```python
+import numpy as np
+import clawhdf5
+
+with clawhdf5.File("data.h5", "r") as f:
+    print(list(f.keys()))              # sorted member names, like h5py
+    ds = f["group/temperatures"]       # relative or absolute ("/group/...") paths
+    print(ds.shape, ds.dtype)          # dtype is the numpy dtype h5py reports
+    block = ds[100:200, ::4]           # a small selection reads only its chunks
+    row = ds[-1]                       # integers drop the axis
+    picked = ds[[1, 5, 9], :]          # one increasing index list per key
+    units = ds.attrs["units"]          # attributes come back as h5py returns them
+    everything = np.asarray(ds)
+
+    records = f["table"]               # compound -> numpy structured array
+    ids = records["id"]                # one field
+```
+
+Reads cover integers and IEEE floats of every width in either byte order,
+`bool`, enums, complex, fixed and variable-length strings, variable-length
+sequences, opaque, HDF5 array types and compounds; other types (references,
+bitfields, ...) raise `TypeError` instead of returning guessed data. Keys
+follow h5py (negative steps, `None` and boolean masks are refused). The
+read itself runs with the GIL released, so Python threads read in parallel.
+A selection whose bounding box covers at most half the dataset decodes only
+the chunks (or contiguous rows) that box overlaps; a larger one — including
+a strided slice across the whole dataset — decodes the whole dataset, as
+do datasets that are compact, virtual, unwritten, or chunked with a
+non-default fill value (`docs/known-issues.md`). An index list is read one
+group of neighbouring chunks at a time.
+Writing (`File(path, "w")`, `create_dataset`, `create_group`, `attrs[...] =`)
+covers `float64`, `float32`, `int64`, `int32` and `uint8` arrays. The tests
+in `crates/clawhdf5-py/tests` compare every read with h5py; run them with
+`pip install pytest h5py && pytest crates/clawhdf5-py/tests`.
+
 ### Agent Memory
 
 ```rust
 use clawhdf5_agent::{HDF5Memory, MemoryConfig, MemoryEntry, AgentMemory};
 
 // Create memory store
-let config = MemoryConfig::new("agent.h5", "my-agent", 384);
+let config = MemoryConfig::new("agent.h5".into(), "my-agent", 384);
 let mut memory = HDF5Memory::create(config)?;
 
 // Save a memory
@@ -278,13 +500,67 @@ memory.save(MemoryEntry {
     tags: "preference".into(),
 })?;
 
-// Search
-let results = memory.search(&query_embedding, 5)?;
+// Hybrid search: vector + BM25, weighted 0.4 / 0.6 (the measured default)
+let results = memory.hybrid_search(&query_embedding, "user preferences", 0.4, 0.6, 5);
 for result in results {
     println!("[{:.3}] {}", result.score, result.chunk);
 }
 ```
 
+### Search Options
+
+```rust
+use clawhdf5_agent::SearchOptions;
+use clawhdf5_agent::confidence::ConfidenceConfig;
+use clawhdf5_agent::reranker::ReRankConfig;
+
+// Only memories from these source channels; still a full page of k results.
+let work = memory.search(
+    &query_embedding,
+    "deadline",
+    &SearchOptions::new(5).with_sources(["slack", "email"]),
+);
+
+// Re-rank by relevance, recency, source authority and activation, then drop
+// low-confidence results — the pipeline ClawhdfBackend runs.
+let careful = memory.search(
+    &query_embedding,
+    "user preferences",
+    &SearchOptions::new(5)
+        .with_rerank(ReRankConfig::default())
+        .with_confidence(ConfidenceConfig::default()),
+);
+```
+
+### Signed Checkpoints
+
+```rust
+use clawhdf5_agent::signing;
+
+// Once, somewhere safe: keep the secret key, publish the public key.
+let key = signing::generate_key();
+let public = key.verifying_key();
+
+// Every checkpoint is signed from now on. The key is never written to disk;
+// a signed store refuses to checkpoint without it.
+memory.set_signing_key(key);
+memory.flush_wal()?;
+
+// Anyone holding the public key can check the file, e.g. after copying it.
+let report = HDF5Memory::verify(std::path::Path::new("agent.h5"), &public)?;
+assert!(report.is_valid());
+// On a tampered file: report.changed_records lists the records that differ.
+```
+
+The signature covers every record (text, embedding as stored, channel,
+timestamp, session, tags, deleted flag, activation), the store's settings,
+its sessions and its knowledge graph — a change made with any tool is caught.
+It covers checkpoints, not saves still in the WAL
+(`report.wal_entries_unsigned` counts those). CLI: `clawhdf5-cli keygen`,
+`--signing-key <file>` on writing commands, and `verify --public-key`.
+Signing adds about 20% to a checkpoint and 32 bytes per record to the file
+([BENCHMARKS.md § Signed checkpoints](BENCHMARKS.md#signed-checkpoints)).
+
 ### Knowledge Graph
 
 ```rust
@@ -309,8 +585,8 @@ let neighbors = kg.bfs_neighbors(alice, 2);  // 2-hop neighborhood
 let activated = kg.spreading_activation(&[alice], 0.5, 0.01, 5);
 
 // Entity resolution — fuzzy matching
-let resolved = kg.resolve_or_create("alice", "person", -1, 2);
-// Returns existing Alice entity (Levenshtein distance ≤ 2)
+let (id, created) = kg.resolve_or_create("alice", "person", -1, 2);
+// id == alice, created == false: matched the existing entity (Levenshtein distance ≤ 2)
 ```
 
 ### Memory Consolidation
@@ -321,15 +597,19 @@ use clawhdf5_agent::consolidation::*;
 let config = ConsolidationConfig::default();
 let mut engine = ConsolidationEngine::new(config);
 
-// Add memories — automatically scored for importance
-engine.add_memory("User prefers dark mode", vec![0.1, 0.2, ...], MemorySource::User);
-engine.add_memory("ok", vec![0.0, 0.0, ...], MemorySource::System);
+let now = 1_700_000_000.0; // seconds since the epoch
+
+// Add memories — automatically scored for importance.
+// Elevated sources (System, …) go through a separate, explicit API.
+let id = engine.add_memory("User prefers dark mode".into(), vec![0.1, 0.2, ...], UntrustedSource::User, now);
+engine.add_trusted_memory("ok".into(), vec![0.0, 0.0, ...], TrustedSource::System, now);
 
 // Access a memory (reactivates it)
-engine.access_memory(0);
+engine.access_memory(id, now);
 
 // Run consolidation cycle
-let stats = engine.consolidate();
+engine.consolidate(now);
+let stats = engine.get_stats();
 // Working memories promote to Episodic (if important enough)
 // Episodic memories promote to Semantic (if accessed enough)
 // Low-decay memories get evicted when tiers are full
@@ -351,19 +631,25 @@ let ids = index.range_query(1700000000.0, 1700010800.0);
 let recent = index.latest(10);
 ```
 
-### OpenClaw Integration
+### Markdown Backend
+
+`ClawhdfBackend` ingests Markdown by section and searches it with the full
+pipeline. It is a library API — clawhdf5 is **not** an OpenClaw memory plugin
+([docs/openclaw.md](docs/openclaw.md)). Sections stored this way carry no
+embedding, so their search is keyword-only unless you save records with
+vectors through `save_entry`.
 
 ```rust
 use clawhdf5_agent::openclaw::*;
 
 // Create backend
-let mut backend = ClawhdfBackend::create("memory.h5", "agent-1", 384)?;
+let mut backend = ClawhdfBackend::create(std::path::Path::new("memory.h5"), 384)?;
 
 // Ingest existing Markdown memory files
 let md = std::fs::read_to_string("MEMORY.md")?;
 let count = backend.ingest_markdown("MEMORY.md", &md)?;
 
-// Search (uses full pipeline: RRF → re-rank → confidence filter)
+// Search (full pipeline: weighted vector + BM25 fusion → re-rank → confidence filter)
 let results = backend.search("user preferences", &query_embedding, 5);
 
 // Export back to Markdown
@@ -375,29 +661,31 @@ let exported = backend.export_markdown("MEMORY.md")?;
 ## Crate Map
 
 ```
-clawhdf5 workspace (16 crates, ~92K lines of Rust; plus libaec-sys, an
-                     internal FFI bindings crate for the optional szip feature)
+clawhdf5 workspace (17 crates, ~86K lines of Rust in src/, ~104K with tests
+                     and benches; plus libaec-sys, an internal FFI bindings
+                     crate for the optional szip feature)
 │
 ├── Core HDF5
-│   ├── clawhdf5-format      — Binary parser/writer (no_std), shared type definitions
-│   ├── clawhdf5-io          — I/O abstraction (buffered, mmap, async)
-│   ├── clawhdf5-filters     — Fast deflate path (zlib-ng); lz4/zstd/pcodec/szip filters live in clawhdf5-format
+│   ├── clawhdf5-format      — Binary parser/writer (no_std-capable), shared type definitions
+│   ├── clawhdf5-io          — I/O abstraction (file/memory readers; optional mmap, async, HSDS, MPI)
+│   ├── clawhdf5-filters     — Fast deflate path (zlib-ng); the filter registry and the lz4/zstd/pcodec/szip/LZF/bitshuffle/bzip2/Blosc filters live in clawhdf5-format
 │   ├── clawhdf5-derive      — Proc macros
 │   ├── clawhdf5             — High-level API
 │   ├── clawhdf5-netcdf4     — NetCDF-4 support
-│   ├── clawhdf5-accel       — SIMD (NEON, AVX2, AVX-512)
+│   ├── clawhdf5-accel       — SIMD (AVX2, NEON incl. SDOT int8; AVX-512 behind `avx512`)
 │   └── clawhdf5-gpu         — GPU compute (wgpu, hand-written WGSL compute shaders)
 │
 ├── Agent Memory
-│   ├── clawhdf5-agent       — Memory engine (20.9K lines, 32 modules; WAL is CRC32-checked per entry)
-│   ├── clawhdf5-ann         — HNSW approximate nearest neighbor (default backend; optional `parallel` feature)
+│   ├── clawhdf5-agent       — Memory engine (24.7K lines, 32 modules; chained-CRC WAL)
+│   ├── clawhdf5-ann         — HNSW approximate nearest neighbor (default backend; f32 or int8 storage; `parallel` build)
 │   ├── clawhdf5-migrate     — SQLite → HDF5 migration
 │   ├── clawhdf5-android     — Android JNI bridge
 │   └── clawhdf5-cli         — CLI tool
 │
 ├── Bindings
 │   ├── clawhdf5-py          — Python (PyO3)
-│   └── clawhdf5-napi        — Node.js (napi-rs)
+│   ├── clawhdf5-napi        — Node.js (napi-rs)
+│   └── clawhdf5-wasm        — Browser (WebAssembly, wasm-bindgen; read-only)
 │
 └── Tooling
     └── clawhdf5-bench       — Benchmark suite
@@ -411,10 +699,10 @@ ClawhDF5's agent memory design draws from 15+ recent papers:
 
 | Paper | Key Insight | ClawhDF5 Module |
 |-------|-------------|-----------------|
-| **MemX** (2026) | RRF + multi-factor re-ranking | `hybrid`, `reranker` |
-| **Graph-Native Cognitive Memory** (2026) | Graph-structured belief revision | `knowledge` |
+| **MemX** (2026) | Hybrid fusion + multi-factor re-ranking | `hybrid`, `reranker` |
+| **Graph-Native Cognitive Memory** (2026) | Graph-structured memory (weighted, timestamped relations; entity timelines) | `knowledge`, `temporal` |
 | **CraniMem** (2026) | Bounded hippocampal memory | `consolidation` |
-| **D-MEM** (2026) | Reward prediction error gating | `consolidation` |
+| **D-MEM** (2026) | Surprise-gated storage (implemented as a novelty score) | `consolidation` |
 | **SYNAPSE** (2025) | Spreading activation for recall | `knowledge` |
 | **RAGdb** (2025) | Zero-dependency edge RAG | Architecture |
 | **MemoryGraft** (2025) | Memory poisoning attacks | `anomaly`, `provenance` |
@@ -429,23 +717,45 @@ ClawhDF5's agent memory design draws from 15+ recent papers:
 
 | Flag | Default | Description |
 |------|---------|-------------|
-| `agent` | no | Full agent memory layer |
-| `float16` | **yes** | Half-precision embedding storage (2× compression) |
+| `float16` | **yes** | Half-precision cosine kernel (`cosine_similarity_f16`). Half-precision *storage* is the `MemoryConfig::float16` setting below, and needs no feature |
 | `hnsw` | **yes** | HNSW approximate vector index for `hybrid_search` (via `clawhdf5-ann`); disable for an exact linear scan |
-
-`MemoryConfig::quantized_index` (off by default) stores the HNSW index's own
-copy of the embeddings as `i8`, roughly halving a loaded store's memory
-(2.72x -> 1.74x the raw vectors at 100k x 384). Quantised distances are
-approximate, so the query path re-scores the candidate pool against the exact
-embeddings the store already holds — recall matches the `f32` index, at about
-13% fewer queries per second. See `BENCHMARKS.md`, "Quantising the index copy".
-| `parallel` | no | Rayon parallel search |
+| `parallel` | **yes** | Parallel HNSW bulk build (same graph, ~3× faster on 16 cores) and Rayon brute-force search strategies |
+| `zstd` | no | Compress embeddings with Zstd instead of deflate when `MemoryConfig::compression` is on (links libzstd) |
 | `fast-math` | no | BLAS matrix-vector multiply |
 | `accelerate` | no | Apple Accelerate / AMX (macOS) |
 | `openblas` | no | OpenBLAS (Linux) |
 | `gpu` | no | GPU search via wgpu |
 | `async` | no | Tokio async with background flush |
 
+To opt out of the parallel build: `--no-default-features --features float16,hnsw`.
+For an exact linear cosine scan instead of HNSW: `--no-default-features --features float16`.
+
+`MemoryConfig::hnsw_m`, `hnsw_ef_construction` and `hnsw_ef_search` tune the
+vector index (16 / 64 / scale-with-`k` by default) and are stored with the
+file.
+
+`MemoryConfig::quantized_index` (**on by default** for new stores) holds the
+HNSW index's own copy of the embeddings as `i8`, roughly halving a loaded
+store's memory (2.72x -> 1.74x the raw vectors at 100k x 384). Quantised
+distances are approximate, so the query path re-scores the candidate pool
+against the exact embeddings the store already holds, which keeps recall at the
+`f32` index's level. It is also **faster**: 1.63x the queries per second at
+equal recall on x86-64 (AVX2) and 1.18x on a Raspberry Pi 5 (NEON `SDOT`), with
+index builds 1.8x and 2.3x faster respectively. Stores created before the
+setting existed keep their `f32` index; opt out for new stores with
+`quantized_index = false` or `clawhdf5-cli create --f32-index`. See
+[BENCHMARKS.md § Quantising the index copy](BENCHMARKS.md#quantising-the-index-copy-quantized_index).
+
+`MemoryConfig::float16` (**on by default** for new stores) stores the
+embeddings on disk as IEEE half precision (numpy `float16`): at 100K × 384 the
+file drops from 154 to 81 MiB, checkpoints and opens get faster, and on the
+full LongMemEval haystack with real MiniLM embeddings every retrieval metric
+matches `f32`. Embeddings are rounded as they are saved, so the store searches
+the same before and after a reopen; values must lie within ±65504. Existing
+stores keep their setting. Opt out with `float16 = false` or
+`clawhdf5-cli create --f32` — e.g. for unnormalised vectors. See
+[BENCHMARKS.md § float16 embedding storage](BENCHMARKS.md#float16-embedding-storage-memoryconfigfloat16).
+
 ### `clawhdf5-format`
 
 | Flag | Default | Description |
@@ -454,26 +764,47 @@ embeddings the store already holds — recall matches the `f32` index, at about
 | `deflate` | yes | Deflate compression |
 | `checksum` | yes | Jenkins lookup3 verification |
 | `provenance` | yes | SHA-256 provenance attributes |
-| `fast-deflate` | **yes** | zlib-ng backend for faster deflate |
-| `system-zlib-decompress` | **yes** | Use the system zlib for decompression where available |
+| `zlib-rs` | **yes** | Pure-Rust deflate backend ([zlib-rs](https://github.com/trifectatechfoundation/zlib-rs)) |
+| `fast-deflate` | no | zlib-ng deflate backend instead (C; needs `cmake`). Overrides `zlib-rs` when both are on |
+| `system-zlib-decompress` | **yes** | Use Apple's system libz for decompression (macOS only; no effect elsewhere) |
 | `parallel` | no | Parallel chunk encoding + compression (rayon) |
 | `fast-checksum` | no | crc32fast-accelerated checksums |
 | `lz4` | no | LZ4 block compression filter (id 32004) |
 | `zstd` | no | Zstandard compression filter (id 32015) |
-| `pcodec` | no | Pcodec lossless numerical codec (id 32023, via `pco` crate) |
-| `system-zlib` / `zlib-rs` | no | Alternative zlib backends for deflate |
+| `pcodec` | no | Pcodec lossless numerical codec (via `pco` crate). Private, unregistered filter id 480: **only clawhdf5 can read these datasets** (h5py/libhdf5 cannot). Files from clawhdf5 <= 2.7.0 used id 32023, which is registered to Granular BitRound; they still read. |
+| `system-zlib` | no | System zlib backend for deflate (C) |
 | `blake3_hash` | no | BLAKE3 content hashing for provenance |
+| `szip` | no | SZIP filter (id 4) via libaec (C, through the internal `libaec-sys` crate) |
+| `lzf` | **yes** | LZF filter (id 32000), h5py's built-in `compression="lzf"`: read and write. No dependencies |
+| `bitshuffle` | no | Bitshuffle filter (id 32008) with its LZ4 and Zstandard modes: read and write. Pure Rust (lz4_flex, ruzstd) |
+| `bzip2` | no | bzip2 filter (id 307): read and write. Pure Rust (the `bzip2` crate's libbz2-rs-sys backend compiles no C) |
+| `blosc` | no | Blosc 1 filter (id 32001): reads BloscLZ, LZ4/LZ4HC, Snappy, Zlib and Zstandard frames with byte or bit shuffle; writes LZ4, Snappy, Zlib or Zstandard (not BloscLZ). Pure Rust |
+| `plugin-filters` | no | All four above |
+
+Blosc2 (32026) and ZFP (32013) are not implemented: reading them fails with
+`UnsupportedFilter`, whose message names the filter. Any other filter can be
+supplied at run time with `filter_registry::register_filter` (a decoder
+closure, or a `FilterCodec` that also encodes). The facade (`clawhdf5`)
+forwards `lzf`, `bitshuffle`, `bzip2`, `blosc` and `plugin-filters`. Write
+with `DatasetBuilder::with_lzf()`, `with_bitshuffle(..)`, `with_bzip2(..)`
+and `with_blosc(..)`; h5py + hdf5plugin read the result (tested both ways in
+`crates/clawhdf5/tests/plugin_filters_interop.rs`). The pure-Rust Zstandard
+encoder has one level (about zstd's level 1); no speed or ratio claims are
+made for these codecs.
 
 ### `clawhdf5-ann`
 
 | Flag | Default | Description |
 |------|---------|-------------|
-| `parallel` | no | Rayon-parallel neighbor-distance computation during HNSW graph pruning |
+| `parallel` | no | Batched bulk build runs neighbour planning and back-link pruning on a Rayon pool; the graph is identical with or without it (enabled by `clawhdf5-agent`'s default `parallel`) |
 
 ### `clawhdf5-io`
 
 | Flag | Default | Description |
 |------|---------|-------------|
+| `mmap` | no | Memory-mapped reads (`memmap2`) |
+| `async` | no | Tokio-based async I/O |
+| `hsds` | no | HSDS (HDF REST service) client |
 | `mpi-io` | no | MPI-backed I/O via the `mpi` crate |
 
 > **Parallel I/O (MPI) limitation:** `mpi-io`'s read path is a root-rank read
@@ -487,17 +818,17 @@ embeddings the store already holds — recall matches the `f32` index, at about
 ## Building
 
 ```bash
-# Default
+# Default (pure Rust: no cmake or C compiler needed)
 cargo build --workspace
 
 # Agent memory with all accelerations (Linux)
-cargo build -p clawhdf5-agent --features "agent,float16,parallel,fast-math"
+cargo build -p clawhdf5-agent --features fast-math
 
 # Agent memory with Apple Accelerate (macOS)
-cargo build -p clawhdf5-agent --features "agent,float16,accelerate,parallel,gpu"
+cargo build -p clawhdf5-agent --features "accelerate,gpu"
 
 # Tests
-cargo test --workspace            # all 1,650+ tests
+cargo test --workspace            # all 1,850+ tests
 cargo test -p clawhdf5-agent      # agent memory tests
 scripts/ci-test.sh                # what CI runs: fmt, clippy matrix, tests,
                                   # h5py/netCDF4 interop, no_std
@@ -519,25 +850,42 @@ cargo bench -p clawhdf5-bench               # h5bench-equivalent I/O suite
 
 ```
 agent_memory.h5
-├── /meta
-│   ├── schema_version: "1.0"
-│   ├── agent_id, embedder, embedding_dim
-│   └── created_at
+├── /meta                          (attributes)
+│   ├── schema_version: "1.0", edgehdf5_version
+│   ├── agent_id, embedder, embedding_dim, chunk_size, overlap, created_at
+│   ├── float16, compression, compression_level, compact_threshold,
+│   │   hebbian_boost, decay_factor, wal_enabled, wal_max_entries
+│   ├── quantized_index, hnsw_m, hnsw_ef_construction, hnsw_ef_search
+│   ├── wal_applied_len, wal_applied_crc   (WAL mark of the last checkpoint)
+│   └── ann_generation                     (ties the .ann sidecar to this checkpoint)
 ├── /memory
 │   ├── chunks:              string[N]
-│   ├── embeddings:  f32[N × D]  (or f16 with float16 flag)
+│   ├── embeddings:          f32[N × D], or f16 for a `float16` store
+│   │                        (chunked; deflate, or Zstd with the `zstd`
+│   │                         feature, when compression is on)
+│   ├── source_channel:      string[N]
+│   ├── timestamps:          f64[N]
+│   ├── session_ids:         string[N]
+│   ├── tags:                string[N]
 │   ├── tombstones:          u8[N]
-│   └── norms:       f32[N]      (pre-computed L2)
+│   ├── norms:               f32[N]      (pre-computed L2)
+│   └── activation_weights:  f32[N]      (Hebbian)
 ├── /sessions
-│   ├── ids:         string[S]
-│   └── summaries:   string[S]
+│   ├── ids, channels, summaries:  string[S]
+│   ├── start_idxs, end_idxs:      i64[S]
+│   └── timestamps:                f64[S]
 └── /knowledge_graph
-    ├── entity_names:    string[E]
-    ├── relation_srcs:   i64[R]
-    ├── relation_tgts:   i64[R]
-    └── relation_types:  string[R]
+    ├── entity_ids, entity_emb_idxs: i64[E]; entity_names, entity_types: string[E]
+    ├── relation_srcs, relation_tgts: i64[R]; relation_types: string[R]
+    ├── relation_weights: f32[R]; relation_ts: f64[R]
+    └── alias_strings: string[A]; alias_entity_ids: i64[A]   (when aliases exist)
 ```
 
+Alongside the store: `<store>.h5.wal` (write-ahead log), `<store>.h5.ann`
+(HNSW graph; derived, safe to delete) and `<store>.h5.lock` (single-writer
+lock). A second writer gets `MemoryError::Locked`; use
+`HDF5Memory::open_read_only` for a lock-free point-in-time view.
+
 ---
 
 ## Migration
@@ -556,9 +904,39 @@ Replace in `Cargo.toml` and source:
 
 ```bash
 cargo install --path crates/clawhdf5-migrate
-clawhdf5-migrate --sqlite old.db --hdf5 memory.h5 --agent-id my-agent --embedding-dim 384
+clawhdf5-migrate --sqlite old.db --hdf5 memory.h5 --agent-id my-agent --embedder minilm
 ```
 
+The output is an ordinary `clawhdf5-agent` store, written through the agent's
+own API: open it with `HDF5Memory::open` (or `clawhdf5-cli --path memory.h5 …`)
+and search it straight away. The source must use the `memory_chunks` / `sessions` / `entities` / `relations` layout (names are
+configurable with `--*-table`); note that this is not ZeroClaw's schema, and
+ZeroClaw does not use clawhdf5. What carries over:
+
+| SQLite | Agent store |
+|--------|-------------|
+| `memory_chunks` | memory records (text, embedding, source channel, timestamp, session id, tags); rows with `deleted = 1` become deleted records, or are left out with `--skip-deleted` |
+| `sessions` | sessions (id, start/end index, channel, summary, timestamp) |
+| `entities`, `relations` | knowledge graph entities and relations; entities get new ids and relations are re-pointed at them |
+
+The chunk `id` column has no counterpart in the agent store, so records are
+written in `id` order and numbered from 0. Embeddings are stored as float16
+like any new store; `--f32` keeps full precision (and is required for values
+beyond ±65504). The embedding dimension is detected from the first row unless
+`--embedding-dim` is given, and every row must have it: a row of another length
+is an error, never truncated or padded. A source with no memory records (only
+sessions or the graph) needs `--embedding-dim`, since a store's dimension is
+fixed when it is created. Every row is checked before the output is created,
+so a source that cannot be migrated leaves an existing store at `--hdf5` as it
+was. `--incremental` adds to an existing store only the rows it does not
+already hold; the source must have the store's dimension, and records already
+in the store take the source's deleted flag (a row deleted in SQLite since the
+last run is deleted in the store; one un-deleted there is written again, as
+the agent has no un-delete). The tool reads the result back with
+`HDF5Memory::open_read_only`, compares it with the source (every row with
+`--validate-full`) and checks that a migrated record is found by search;
+`--dry-run` only counts the rows.
+
 ---
 
 ## Roadmap
@@ -572,10 +950,10 @@ See [ROADMAP.md](ROADMAP.md) for the full implementation tracker.
 - ✅ Temporal reasoning with sub-µs queries
 - ✅ Memory security + anomaly detection
 - ✅ Multi-modal memory (text/image/audio/video)
-- ✅ OpenClaw integration layer
+- ✅ Markdown ingest/export backend (`ClawhdfBackend`); an OpenClaw plugin was never built — see [docs/openclaw.md](docs/openclaw.md)
 - ✅ Comprehensive Criterion benchmarks
 
-**Phase 2** — MemoryArena and LongMemEval academic benchmarks are done (see [BENCHMARKS.md](BENCHMARKS.md), reproduced on a second machine); remaining: publish the OpenClaw TypeScript bridge to npm, crates.io/PyPI publishing.
+**Phase 2** — MemoryArena and LongMemEval academic benchmarks are done (see [BENCHMARKS.md](BENCHMARKS.md), reproduced on a second machine); remaining: crates.io/PyPI publishing. The Node bindings are unpublished and known to be broken ([known issues](docs/known-issues.md)).
 
 ---
 
@@ -592,6 +970,6 @@ MIT
 ---
 
 <p align="center">
-  <em>Built by <a href="https://github.com/redclawsystems">RedClaw Systems</a></em><br>
-  <em>~92,000 lines of Rust. Zero C dependencies. One file to remember everything.</em>
+  <em>Built by <a href="https://git.redclaw.dev/quantumclaw">RedClaw Systems</a></em><br>
+  <em>~86,000 lines of Rust. Zero C dependencies. One file to remember everything.</em>
 </p>

ROADMAP.md

@@ -105,24 +105,30 @@
 
 ---
 
-## Track 7: OpenClaw Integration
-**Status:** 🟢 Complete
+## Track 7: OpenClaw Integration — withdrawn (2026-09-25)
+**Status:** ⚪ Withdrawn (the items below were library work; no OpenClaw integration shipped)
 **Priority:** Critical (for adoption)
 **Crates:** `clawhdf5-agent`, `clawhdf5-napi`
 
 - [x] **7.1** Memory backend trait — MemoryBackend with search/get/write/ingest/export/stats
 - [x] **7.2** Hybrid retrieval pipeline — ClawhdfBackend wires RRF → reranker → confidence rejection
 - [x] **7.3** Markdown import/export — MarkdownParser + MarkdownExporter with line tracking + metadata
-- [x] **7.4** memory_search tool — backed by full hybrid retrieval pipeline
-- [x] **7.5** memory_get tool — get() with path + line range support
+- [x] **7.4** `search()` — backed by the full hybrid retrieval pipeline (a Rust method; no OpenClaw tool was ever registered)
+- [x] **7.5** `get()` — read back by path, with a line slice (not an OpenClaw tool either)
 - [x] **7.6** Compaction integration — run_compaction() (decay + compact + WAL flush), run_consolidation() (hippocampal engine), tick_session(), flush_wal()
-- [x] **7.7** Config surface — `memory.backend = "clawhdf5"` schema documented in docs/openclaw-config.md
-- [x] **7.8** Documentation + migration guide — docs/migration-guide.md, docs/openclaw-integration.md (architecture, full API reference, code patterns)
+- [ ] **7.7** ~~Config surface — `memory.backend = "clawhdf5"`~~ — never valid OpenClaw config; docs removed
+- [ ] **7.8** ~~Documentation + migration guide~~ — removed: they described an integration that never worked
 
-**Node.js bridge:** `clawhdf5-napi` (napi-rs) → `@redclaw/clawhdf5` npm package with full TypeScript types.
+**Node.js bridge:** `clawhdf5-napi` (napi-rs) and a TypeScript wrapper in `packages/clawhdf5-node` exist but are unpublished, untested in CI and known to be broken (docs/known-issues.md).
 
 ---
 
+> **Withdrawn.** None of this track produced a working OpenClaw integration: no
+> plugin was built, the documented `memory.backend = "clawhdf5"` config was never
+> valid in any OpenClaw release, and the Node package was never published. The
+> Rust `ClawhdfBackend` remains as a library API. Not pursued for now; see
+> [docs/openclaw.md](docs/openclaw.md) for what a plugin would need today.
+
 ## Track 8: Benchmarking & Validation
 **Status:** 🟢 Complete
 **Priority:** High
@@ -142,7 +148,7 @@
 
 **Phase 1:** ~~Tracks 1, 2, 3 — core memory intelligence~~ 🟢 Complete
 **Phase 2:** ~~Track 4 (temporal) + Track 5 (security)~~ 🟢 Complete
-**Phase 3:** ~~Track 6 (multi-modal) + Track 7 (OpenClaw integration)~~ 🟢 Complete
+**Phase 3:** ~~Track 6 (multi-modal)~~ 🟢 Complete; Track 7 (OpenClaw integration) withdrawn
 **Phase 4:** ~~Track 8 (benchmarking + validation)~~ 🟢 Complete
 
 All 8 tracks delivered. 1,650+ tests passing, zero clippy warnings.

conformance/.gitignore

@@ -0,0 +1,3 @@
+/.cache/
+# pin the probe's dependencies (the workspace lock is not committed)
+!/probe/Cargo.lock

conformance/README.md

@@ -0,0 +1,39 @@
+# Conformance sweep
+
+Reads every HDF5 file of eight public corpora with clawhdf5 and with
+h5py/libhdf5, compares the two readings object by object, and writes
+[`CONFORMANCE.md`](../CONFORMANCE.md).
+
+```sh
+CLAWHDF5_PYTHON=/path/to/venv/bin/python conformance/run.sh      # ~30 s once the corpus is cached
+conformance/run.sh --update-baseline                             # after an intended change in results
+```
+
+Needs Rust, `git`, `h5dump` (Debian/Ubuntu `hdf5-tools`), `libaec` (for the
+probe's `szip` feature; `libaec-dev`), and a Python with the packages in
+`requirements.txt`. The first run downloads about 450 MB of sparse checkouts.
+
+| file | role |
+|---|---|
+| `corpus.txt` | the corpora: git URL, pinned commit, swept root, sparse-checkout patterns |
+| `fetch-corpus.sh` | shallow, sparse, blob-filtered checkout of each pinned commit into `.cache/src/` (gitignored); no-op when already there |
+| `list_files.py` | which files are probed (HDF5/netCDF-4 extensions minus netCDF classic, plus the CVE reproducers) |
+| `probe/` | the clawhdf5 side: a standalone crate (outside the workspace, so `cargo test --workspace` never builds it) that walks a file with `clawhdf5-format` and prints canonical JSON |
+| `ref.py` | the h5py side: the same JSON from h5py |
+| `run_one.sh` | runs both sides on one file (and `h5dump` on the CVE corpus) under a timeout and an address-space limit |
+| `compare.py` | classifies each file (ok / our-error / mismatch / h5py-cannot-read / panic / hang / crash / oom) and groups root causes |
+| `report.py` | writes `CONFORMANCE.md` |
+| `check.py` | the gate: fails on any panic/hang/crash/oom, on an ok count below `baseline.json`, or on a baseline-ok file that is no longer ok |
+| `baseline.json` | the ok files the gate holds the line on |
+| `requirements.txt` | pinned h5py / numpy / hdf5plugin / netCDF4 |
+
+Results for every file (both sides' JSON and stderr, `results.csv`,
+`results.json`, `summary.md`) are left in `.cache/results/`.
+
+The nightly job is `.gitea/workflows/conformance.yml`; it prints the report
+into the job log.
+
+The canonical value encoding both sides hash is documented at the top of
+`probe/src/main.rs`. Values are compared as libhdf5 presents them: a float
+with a non-IEEE bit layout (N-Bit) or an integer with a bit offset is compared
+as the converted number, not as raw file bytes.

conformance/baseline.json

@@ -0,0 +1,624 @@
+{
+ "comment": "conformance/run.sh fails if the ok count drops below `ok` or a file in `ok_files` stops being ok. Regenerate with `conformance/run.sh --update-baseline` after an intended change.",
+ "commit": "73a01f1256fb9bf1b1e7601f755af9e8273cec4e",
+ "date": "2026-09-26 14:18 UTC",
+ "reference": "h5py 3.16.0 / HDF5 2.0.0",
+ "files": 697,
+ "ok": 575,
+ "counts": {
+  "h5py-cannot-read": 92,
+  "mismatch": 20,
+  "ok": 575,
+  "our-error": 10
+ },
+ "per_corpus": {
+  "NCAS-CMS_pyfive": {
+   "mismatch": 1,
+   "ok": 32
+  },
+  "cve_hdf5": {
+   "h5py-cannot-read": 32,
+   "mismatch": 9,
+   "ok": 100,
+   "our-error": 6
+  },
+  "h5py_data": {
+   "ok": 4
+  },
+  "hdf5": {
+   "h5py-cannot-read": 60,
+   "mismatch": 10,
+   "ok": 392,
+   "our-error": 4
+  },
+  "netcdf-c": {
+   "ok": 20
+  },
+  "netcdf4-python": {
+   "ok": 18
+  },
+  "usnistgov_h5wasm": {
+   "ok": 5
+  },
+  "xarray-data": {
+   "ok": 4
+  }
+ },
+ "ok_files": [
+  "NCAS-CMS_pyfive/tests/compact.hdf5",
+  "NCAS-CMS_pyfive/tests/data/btreev2.hdf5",
+  "NCAS-CMS_pyfive/tests/data/chunked.hdf5",
+  "NCAS-CMS_pyfive/tests/data/cmip_bad_eg.nc",
+  "NCAS-CMS_pyfive/tests/data/compressed.hdf5",
+  "NCAS-CMS_pyfive/tests/data/compressed_v1.hdf5",
+  "NCAS-CMS_pyfive/tests/data/dataset_datatypes.hdf5",
+  "NCAS-CMS_pyfive/tests/data/dataset_multidim.hdf5",
+  "NCAS-CMS_pyfive/tests/data/dim_scales.hdf5",
+  "NCAS-CMS_pyfive/tests/data/earliest.hdf5",
+  "NCAS-CMS_pyfive/tests/data/enum_h5variable.hdf5",
+  "NCAS-CMS_pyfive/tests/data/enum_variable.hdf5",
+  "NCAS-CMS_pyfive/tests/data/enum_variable.nc",
+  "NCAS-CMS_pyfive/tests/data/enums_from_netcdf.nc",
+  "NCAS-CMS_pyfive/tests/data/fillvalue_earliest.hdf5",
+  "NCAS-CMS_pyfive/tests/data/fillvalue_latest.hdf5",
+  "NCAS-CMS_pyfive/tests/data/filter_pipeline_v2.hdf5",
+  "NCAS-CMS_pyfive/tests/data/fletcher32.hdf5",
+  "NCAS-CMS_pyfive/tests/data/fractal_heap_no_mci_rlat.nc",
+  "NCAS-CMS_pyfive/tests/data/groups.hdf5",
+  "NCAS-CMS_pyfive/tests/data/h5netcdf_test.hdf5",
+  "NCAS-CMS_pyfive/tests/data/issue23_A.nc",
+  "NCAS-CMS_pyfive/tests/data/issue23_A_contiguous.nc",
+  "NCAS-CMS_pyfive/tests/data/issue23_B.nc",
+  "NCAS-CMS_pyfive/tests/data/latest.hdf5",
+  "NCAS-CMS_pyfive/tests/data/netcdf4_classic.nc",
+  "NCAS-CMS_pyfive/tests/data/new_style_groups.hdf5",
+  "NCAS-CMS_pyfive/tests/data/noy_AERmonZ_UKESM1-0-LL_piControl_r1i1p1f2_gnz_200001-200012.nc",
+  "NCAS-CMS_pyfive/tests/data/references.hdf5",
+  "NCAS-CMS_pyfive/tests/data/resizable.hdf5",
+  "NCAS-CMS_pyfive/tests/opaque_datetime.hdf5",
+  "NCAS-CMS_pyfive/tests/opaque_fixed.hdf5",
+  "cve_hdf5/cvefiles/cve-2016-4330.h5",
+  "cve_hdf5/cvefiles/cve-2016-4331.h5",
+  "cve_hdf5/cvefiles/cve-2016-4332-mtime-new.h5",
+  "cve_hdf5/cvefiles/cve-2016-4332-mtime.h5",
+  "cve_hdf5/cvefiles/cve-2016-4333.h5",
+  "cve_hdf5/cvefiles/cve-2017-17505.h5",
+  "cve_hdf5/cvefiles/cve-2017-17506.h5",
+  "cve_hdf5/cvefiles/cve-2017-17507.h5",
+  "cve_hdf5/cvefiles/cve-2017-17508.h5",
+  "cve_hdf5/cvefiles/cve-2017-17509.h5",
+  "cve_hdf5/cvefiles/cve-2018-11202.h5",
+  "cve_hdf5/cvefiles/cve-2018-11203.h5",
+  "cve_hdf5/cvefiles/cve-2018-11204.h5",
+  "cve_hdf5/cvefiles/cve-2018-11205.h5",
+  "cve_hdf5/cvefiles/cve-2018-11206-new.h5",
+  "cve_hdf5/cvefiles/cve-2018-11206-old.h5",
+  "cve_hdf5/cvefiles/cve-2018-11207.h5",
+  "cve_hdf5/cvefiles/cve-2018-13867.h5",
+  "cve_hdf5/cvefiles/cve-2018-13868.h5",
+  "cve_hdf5/cvefiles/cve-2018-13869.h5",
+  "cve_hdf5/cvefiles/cve-2018-13870.h5",
+  "cve_hdf5/cvefiles/cve-2018-13871.h5",
+  "cve_hdf5/cvefiles/cve-2018-13872.h5",
+  "cve_hdf5/cvefiles/cve-2018-13873.h5",
+  "cve_hdf5/cvefiles/cve-2018-13875.h5",
+  "cve_hdf5/cvefiles/cve-2018-14031.h5",
+  "cve_hdf5/cvefiles/cve-2018-14033.h5",
+  "cve_hdf5/cvefiles/cve-2018-14034.h5",
+  "cve_hdf5/cvefiles/cve-2018-14035.h5",
+  "cve_hdf5/cvefiles/cve-2018-14460.h5",
+  "cve_hdf5/cvefiles/cve-2018-15671.h5",
+  "cve_hdf5/cvefiles/cve-2018-15672.h5",
+  "cve_hdf5/cvefiles/cve-2018-16438.h5",
+  "cve_hdf5/cvefiles/cve-2018-17233.h5",
+  "cve_hdf5/cvefiles/cve-2018-17234.h5",
+  "cve_hdf5/cvefiles/cve-2018-17237.h5",
+  "cve_hdf5/cvefiles/cve-2018-17432.h5",
+  "cve_hdf5/cvefiles/cve-2018-17434.h5",
+  "cve_hdf5/cvefiles/cve-2018-17435.h5",
+  "cve_hdf5/cvefiles/cve-2018-17437.h5",
+  "cve_hdf5/cvefiles/cve-2019-8396.h5",
+  "cve_hdf5/cvefiles/cve-2019-9152.h5",
+  "cve_hdf5/cvefiles/cve-2020-10811.h5",
+  "cve_hdf5/cvefiles/cve-2020-18232.h5",
+  "cve_hdf5/cvefiles/cve-2021-36977.h5",
+  "cve_hdf5/cvefiles/cve-2021-37501.h5",
+  "cve_hdf5/cvefiles/cve-2021-45829.h5",
+  "cve_hdf5/cvefiles/cve-2021-45833.h5",
+  "cve_hdf5/cvefiles/cve-2024-29157.h5",
+  "cve_hdf5/cvefiles/cve-2024-29158.h5",
+  "cve_hdf5/cvefiles/cve-2024-29159.h5",
+  "cve_hdf5/cvefiles/cve-2024-29160.h5",
+  "cve_hdf5/cvefiles/cve-2024-29161.h5",
+  "cve_hdf5/cvefiles/cve-2024-29162.h5",
+  "cve_hdf5/cvefiles/cve-2024-29163.h5",
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+  "hdf5/tools/test/testfiles/tbfloat16_be.h5",
+  "hdf5/tools/test/testfiles/tbigdims.h5",
+  "hdf5/tools/test/testfiles/tbinary.h5",
+  "hdf5/tools/test/testfiles/tbitnopaque.h5",
+  "hdf5/tools/test/testfiles/tchar.h5",
+  "hdf5/tools/test/testfiles/tcmpdattrintsize.h5",
+  "hdf5/tools/test/testfiles/tcmpdintarray.h5",
+  "hdf5/tools/test/testfiles/tcmpdints.h5",
+  "hdf5/tools/test/testfiles/tcmpdintsize.h5",
+  "hdf5/tools/test/testfiles/tcomplex.h5",
+  "hdf5/tools/test/testfiles/tcompound.h5",
+  "hdf5/tools/test/testfiles/tcompound_complex.h5",
+  "hdf5/tools/test/testfiles/tcompound_complex2.h5",
+  "hdf5/tools/test/testfiles/tdatareg.h5",
+  "hdf5/tools/test/testfiles/tdset.h5",
+  "hdf5/tools/test/testfiles/tdset2.h5",
+  "hdf5/tools/test/testfiles/tdset_idx.h5",
+  "hdf5/tools/test/testfiles/tempty.h5",
+  "hdf5/tools/test/testfiles/textlink.h5",
+  "hdf5/tools/test/testfiles/textlinkfar.h5",
+  "hdf5/tools/test/testfiles/textlinksrc.h5",
+  "hdf5/tools/test/testfiles/textlinktar.h5",
+  "hdf5/tools/test/testfiles/textpfe.h5",
+  "hdf5/tools/test/testfiles/tfcontents2.h5",
+  "hdf5/tools/test/testfiles/tfilters.h5",
+  "hdf5/tools/test/testfiles/tfloat16.h5",
+  "hdf5/tools/test/testfiles/tfloat16_be.h5",
+  "hdf5/tools/test/testfiles/tfloat4.h5",
+  "hdf5/tools/test/testfiles/tfloat6.h5",
+  "hdf5/tools/test/testfiles/tfloat8.h5",
+  "hdf5/tools/test/testfiles/tfloatsattrs.h5",
+  "hdf5/tools/test/testfiles/tfpformat.h5",
+  "hdf5/tools/test/testfiles/tfvalues.h5",
+  "hdf5/tools/test/testfiles/tgroup.h5",
+  "hdf5/tools/test/testfiles/tgrp_comments.h5",
+  "hdf5/tools/test/testfiles/tgrpnullspace.h5",
+  "hdf5/tools/test/testfiles/thlink.h5",
+  "hdf5/tools/test/testfiles/thyperslab.h5",
+  "hdf5/tools/test/testfiles/tintascii.h5",
+  "hdf5/tools/test/testfiles/tints4dims.h5",
+  "hdf5/tools/test/testfiles/tintsattrs.h5",
+  "hdf5/tools/test/testfiles/tintsnodata.h5",
+  "hdf5/tools/test/testfiles/tlarge_objname.h5",
+  "hdf5/tools/test/testfiles/tldouble.h5",
+  "hdf5/tools/test/testfiles/tldouble_scalar.h5",
+  "hdf5/tools/test/testfiles/tlonglinks.h5",
+  "hdf5/tools/test/testfiles/tloop.h5",
+  "hdf5/tools/test/testfiles/tnamed_dtype_attr.h5",
+  "hdf5/tools/test/testfiles/tnestedcmpddt.h5",
+  "hdf5/tools/test/testfiles/tnestedcomp.h5",
+  "hdf5/tools/test/testfiles/tno-subset.h5",
+  "hdf5/tools/test/testfiles/tnullspace.h5",
+  "hdf5/tools/test/testfiles/torderattr.h5",
+  "hdf5/tools/test/testfiles/tordergr.h5",
+  "hdf5/tools/test/testfiles/trefer_attr.h5",
+  "hdf5/tools/test/testfiles/trefer_compat.h5",
+  "hdf5/tools/test/testfiles/trefer_ext1.h5",
+  "hdf5/tools/test/testfiles/trefer_ext2.h5",
+  "hdf5/tools/test/testfiles/trefer_grp.h5",
+  "hdf5/tools/test/testfiles/trefer_obj.h5",
+  "hdf5/tools/test/testfiles/trefer_obj_del.h5",
+  "hdf5/tools/test/testfiles/trefer_param.h5",
+  "hdf5/tools/test/testfiles/trefer_reg.h5",
+  "hdf5/tools/test/testfiles/trefer_reg_1d.h5",
+  "hdf5/tools/test/testfiles/tsaf.h5",
+  "hdf5/tools/test/testfiles/tscalarattrintsize.h5",
+  "hdf5/tools/test/testfiles/tscalarintattrsize.h5",
+  "hdf5/tools/test/testfiles/tscalarintsize.h5",
+  "hdf5/tools/test/testfiles/tscalarstring.h5",
+  "hdf5/tools/test/testfiles/tslink.h5",
+  "hdf5/tools/test/testfiles/tsoftlinks.h5",
+  "hdf5/tools/test/testfiles/tst_onion_dset_1d.h5",
+  "hdf5/tools/test/testfiles/tst_onion_dset_ext.h5",
+  "hdf5/tools/test/testfiles/tst_onion_objs.h5",
+  "hdf5/tools/test/testfiles/tstr.h5",
+  "hdf5/tools/test/testfiles/tstr2.h5",
+  "hdf5/tools/test/testfiles/tstr3.h5",
+  "hdf5/tools/test/testfiles/tudfilter.h5",
+  "hdf5/tools/test/testfiles/tudfilter2.h5",
+  "hdf5/tools/test/testfiles/tvldtypes1.h5",
+  "hdf5/tools/test/testfiles/tvldtypes2.h5",
+  "hdf5/tools/test/testfiles/tvldtypes3.h5",
+  "hdf5/tools/test/testfiles/tvldtypes4.h5",
+  "hdf5/tools/test/testfiles/tvldtypes5.h5",
+  "hdf5/tools/test/testfiles/tvlenstr_array.h5",
+  "hdf5/tools/test/testfiles/tvlstr.h5",
+  "hdf5/tools/test/testfiles/tvms.h5",
+  "hdf5/tools/test/testfiles/txtfp32.h5",
+  "hdf5/tools/test/testfiles/txtfp64.h5",
+  "hdf5/tools/test/testfiles/txtin16.h5",
+  "hdf5/tools/test/testfiles/txtin32.h5",
+  "hdf5/tools/test/testfiles/txtin8.h5",
+  "hdf5/tools/test/testfiles/txtstr.h5",
+  "hdf5/tools/test/testfiles/txtuin16.h5",
+  "hdf5/tools/test/testfiles/txtuin32.h5",
+  "hdf5/tools/test/testfiles/vds/1_a.h5",
+  "hdf5/tools/test/testfiles/vds/1_b.h5",
+  "hdf5/tools/test/testfiles/vds/1_c.h5",
+  "hdf5/tools/test/testfiles/vds/1_d.h5",
+  "hdf5/tools/test/testfiles/vds/1_e.h5",
+  "hdf5/tools/test/testfiles/vds/1_f.h5",
+  "hdf5/tools/test/testfiles/vds/1_vds.h5",
+  "hdf5/tools/test/testfiles/vds/2_a.h5",
+  "hdf5/tools/test/testfiles/vds/2_b.h5",
+  "hdf5/tools/test/testfiles/vds/2_c.h5",
+  "hdf5/tools/test/testfiles/vds/2_d.h5",
+  "hdf5/tools/test/testfiles/vds/2_e.h5",
+  "hdf5/tools/test/testfiles/vds/2_vds.h5",
+  "hdf5/tools/test/testfiles/vds/3_1_vds.h5",
+  "hdf5/tools/test/testfiles/vds/3_2_vds.h5",
+  "hdf5/tools/test/testfiles/vds/4_0.h5",
+  "hdf5/tools/test/testfiles/vds/4_1.h5",
+  "hdf5/tools/test/testfiles/vds/4_2.h5",
+  "hdf5/tools/test/testfiles/vds/4_vds.h5",
+  "hdf5/tools/test/testfiles/vds/5_a.h5",
+  "hdf5/tools/test/testfiles/vds/5_b.h5",
+  "hdf5/tools/test/testfiles/vds/5_c.h5",
+  "hdf5/tools/test/testfiles/vds/5_vds.h5",
+  "hdf5/tools/test/testfiles/vds/a.h5",
+  "hdf5/tools/test/testfiles/vds/b.h5",
+  "hdf5/tools/test/testfiles/vds/c.h5",
+  "hdf5/tools/test/testfiles/vds/d.h5",
+  "hdf5/tools/test/testfiles/vds/f-0.h5",
+  "hdf5/tools/test/testfiles/vds/f-3.h5",
+  "hdf5/tools/test/testfiles/vds/vds-eiger.h5",
+  "hdf5/tools/test/testfiles/vds/vds-percival-unlim-maxmin.h5",
+  "hdf5/tools/test/testfiles/xml/tbitfields.h5",
+  "hdf5/tools/test/testfiles/xml/tcompound2.h5",
+  "hdf5/tools/test/testfiles/xml/tdset2.h5",
+  "hdf5/tools/test/testfiles/xml/tenum.h5",
+  "hdf5/tools/test/testfiles/xml/test35.nc",
+  "hdf5/tools/test/testfiles/xml/tloop2.h5",
+  "hdf5/tools/test/testfiles/xml/tname-amp.h5",
+  "hdf5/tools/test/testfiles/xml/tname-apos.h5",
+  "hdf5/tools/test/testfiles/xml/tname-gt.h5",
+  "hdf5/tools/test/testfiles/xml/tname-lt.h5",
+  "hdf5/tools/test/testfiles/xml/tname-quot.h5",
+  "hdf5/tools/test/testfiles/xml/tname-sp.h5",
+  "hdf5/tools/test/testfiles/xml/tnodata.h5",
+  "hdf5/tools/test/testfiles/xml/tobjref.h5",
+  "hdf5/tools/test/testfiles/xml/topaque.h5",
+  "hdf5/tools/test/testfiles/xml/tref-escapes-at.h5",
+  "hdf5/tools/test/testfiles/xml/tref-escapes.h5",
+  "hdf5/tools/test/testfiles/xml/tref.h5",
+  "hdf5/tools/test/testfiles/xml/tstring-at.h5",
+  "hdf5/tools/test/testfiles/xml/tstring.h5",
+  "hdf5/tools/test/testfiles/zerodim.h5",
+  "netcdf-c/h5_test/ref_tst_h_compounds.h5",
+  "netcdf-c/h5_test/ref_tst_h_compounds2.h5",
+  "netcdf-c/nc_test4/ref_hdf5_compat1.nc",
+  "netcdf-c/nc_test4/ref_hdf5_compat2.nc",
+  "netcdf-c/nc_test4/ref_hdf5_compat3.nc",
+  "netcdf-c/nc_test4/ref_szip.h5",
+  "netcdf-c/nc_test4/ref_tst_compounds.nc",
+  "netcdf-c/nc_test4/ref_tst_dims.nc",
+  "netcdf-c/nc_test4/ref_tst_interops4.nc",
+  "netcdf-c/nc_test4/ref_tst_xplatform2_1.nc",
+  "netcdf-c/nc_test4/ref_tst_xplatform2_2.nc",
+  "netcdf-c/nc_test4/tdset.h5",
+  "netcdf-c/ncdump/ref_nc_test_netcdf4_4_0.nc",
+  "netcdf-c/ncdump/ref_no_ncproperty.nc",
+  "netcdf-c/ncdump/ref_provenance_v1.nc",
+  "netcdf-c/ncdump/ref_test_corrupt_magic.nc",
+  "netcdf-c/ncdump/ref_tst_compounds2.nc",
+  "netcdf-c/ncdump/ref_tst_compounds3.nc",
+  "netcdf-c/ncdump/ref_tst_compounds4.nc",
+  "netcdf-c/ncdump/ref_tst_irish_rover.nc",
+  "netcdf4-python/examples/data/prmsl.2000.nc",
+  "netcdf4-python/examples/data/prmsl.2001.nc",
+  "netcdf4-python/examples/data/prmsl.2002.nc",
+  "netcdf4-python/examples/data/prmsl.2003.nc",
+  "netcdf4-python/examples/data/prmsl.2004.nc",
+  "netcdf4-python/examples/data/prmsl.2005.nc",
+  "netcdf4-python/examples/data/prmsl.2006.nc",
+  "netcdf4-python/examples/data/prmsl.2007.nc",
+  "netcdf4-python/examples/data/prmsl.2008.nc",
+  "netcdf4-python/examples/data/prmsl.2009.nc",
+  "netcdf4-python/examples/data/prmsl.2010.nc",
+  "netcdf4-python/examples/data/prmsl.2011.nc",
+  "netcdf4-python/examples/data/rtofs_glo_3dz_f006_6hrly_reg3.nc",
+  "netcdf4-python/test/20171025_2056.Cloud_Top_Height.nc",
+  "netcdf4-python/test/issue1152.nc",
+  "netcdf4-python/test/issue671.nc",
+  "netcdf4-python/test/issue672.nc",
+  "netcdf4-python/test/test_gold.nc",
+  "usnistgov_h5wasm/test/array.h5",
+  "usnistgov_h5wasm/test/compressed.h5",
+  "usnistgov_h5wasm/test/empty.h5",
+  "usnistgov_h5wasm/test/float16.h5",
+  "usnistgov_h5wasm/test/vlen.h5",
+  "xarray-data/ROMS_example.nc",
+  "xarray-data/basin_mask.nc",
+  "xarray-data/imerghh_730.hdf5",
+  "xarray-data/precipitation.nc4"
+ ]
+}

conformance/check.py

@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+"""check.py <results_dir> <baseline.json> [--update]
+
+The conformance gate. Fails (exit 1) when
+  * clawhdf5 panicked, hung, crashed or ran out of memory on any file, or
+  * the ok count fell below the baseline's, or
+  * a file the baseline lists as ok is no longer ok (even if another file
+    became ok and the total held).
+New ok files are reported so the baseline can be raised (--update rewrites it
+from the results).
+"""
+import json
+import os
+import sys
+
+FATAL = ("panic", "hang", "crash", "oom")
+
+
+def main():
+    args = [a for a in sys.argv[1:] if not a.startswith("--")]
+    update = "--update" in sys.argv
+    res_dir, base_path = args
+    res = json.load(open(os.path.join(res_dir, "results.json")))
+    rows = res["rows"]
+    counts = {}
+    per_corpus = {}
+    for r in rows:
+        counts[r["class"]] = counts.get(r["class"], 0) + 1
+        pc = per_corpus.setdefault(r["corpus"], {})
+        pc[r["class"]] = pc.get(r["class"], 0) + 1
+    ok_files = sorted(r["file"] for r in rows if r["class"] == "ok")
+
+    if update:
+        meta = {}
+        mp = os.path.join(res_dir, "report-meta.json")
+        if os.path.exists(mp):
+            meta = json.load(open(mp))
+        base = {
+            "comment": "conformance/run.sh fails if the ok count drops below `ok` or a file in `ok_files` stops being ok. "
+                       "Regenerate with `conformance/run.sh --update-baseline` after an intended change.",
+            "commit": meta.get("commit", ""),
+            "date": meta.get("date", ""),
+            "reference": meta.get("reference", ""),
+            "files": len(rows),
+            "ok": len(ok_files),
+            "counts": dict(sorted(counts.items())),
+            "per_corpus": {k: dict(sorted(v.items())) for k, v in sorted(per_corpus.items())},
+            "ok_files": ok_files,
+        }
+        with open(base_path, "w") as fh:
+            json.dump(base, fh, indent=1)
+            fh.write("\n")
+        print(f"baseline updated: {len(ok_files)} ok of {len(rows)} files -> {base_path}")
+        return 0
+
+    base = json.load(open(base_path))
+    failures = []
+    fatal = [r for r in rows if r["class"] in FATAL]
+    for r in fatal:
+        failures.append(f"{r['class']}: {r['file']}: {r['ours_detail'][:200]}")
+    if len(ok_files) < base["ok"]:
+        failures.append(f"ok count dropped: {len(ok_files)} < baseline {base['ok']}")
+    now_ok = set(ok_files)
+    by_file = {r["file"]: r for r in rows}
+    for f in base["ok_files"]:
+        if f not in now_ok:
+            r = by_file.get(f)
+            why = f"now {r['class']}: {(r['ours_detail'] or r['first_issue'])[:200]}" if r else "no longer in the corpus"
+            failures.append(f"regressed: {f}: {why}")
+    gained = sorted(now_ok - set(base["ok_files"]))
+
+    print(f"conformance: {len(ok_files)} ok of {len(rows)} files (baseline {base['ok']} of {base['files']}); "
+          + ", ".join(f"{k} {v}" for k, v in sorted(counts.items())))
+    if gained:
+        print(f"{len(gained)} file(s) newly ok — raise the baseline with `conformance/run.sh --update-baseline`:")
+        for f in gained:
+            print(f"  + {f}")
+    if failures:
+        print(f"CONFORMANCE GATE FAILED ({len(failures)}):")
+        for f in failures:
+            print(f"  - {f}")
+        return 1
+    print("conformance gate passed")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

conformance/compare.py

@@ -0,0 +1,289 @@
+#!/usr/bin/env python3
+"""compare.py <results_dir>: classify each file and group failures by root cause.
+
+Writes <results_dir>/results.csv, results.json and summary.md.
+File classes (first match wins):
+  hang, oom, crash, panic       ours: timeout / allocation failure / signal / any panic (caught or not)
+  h5py-cannot-read              libhdf5/h5py failed to open the file (or crashed/hung)
+  our-error                     we fail to open, list, or read something h5py reads
+  mismatch                      we read something with different shape/values, or a different object set
+  ok
+"""
+import collections
+import csv
+import json
+import os
+import re
+import sys
+
+R = sys.argv[1]
+RUNS = os.path.join(R, "runs")
+
+
+def load(d, name):
+    rc_p = os.path.join(d, name + ".rc")
+    if not os.path.exists(rc_p):
+        return None
+    rc = int(open(rc_p).read().strip() or -1)
+    err = open(os.path.join(d, name + ".err"), errors="replace").read()
+    js = None
+    try:
+        js = json.load(open(os.path.join(d, name + ".json")))
+    except Exception:  # noqa: BLE001
+        pass
+    return {"rc": rc, "err": err, "json": js}
+
+
+def proc_status(p):
+    """-> (status, detail)"""
+    if p is None:
+        return "missing", ""
+    rc, err = p["rc"], p["err"]
+    first_panic = next((ln for ln in err.splitlines() if ln.startswith("PANIC:") or "panicked at" in ln), "")
+    if rc == 0 and p["json"] is not None:
+        return "ok", ""
+    if rc == 137 or rc == 124:
+        return "hang", f"timeout ({os.environ.get('TMO', '20')} s)"
+    if "memory allocation of" in err or "MemoryError" in err or "std::bad_alloc" in err:
+        m = re.search(r"memory allocation of \d+ bytes failed", err)
+        return "oom", m.group(0) if m else "allocation failure"
+    if "overflowed its stack" in err:
+        return "crash", "stack overflow"
+    if rc == 101:
+        return "panic", first_panic or (err.strip().splitlines() or [""])[-1]
+    if rc in (134, 139, 136, 135, 132) or rc > 128:
+        sig = {134: "SIGABRT", 139: "SIGSEGV", 136: "SIGFPE", 135: "SIGBUS", 132: "SIGILL"}.get(rc, f"signal {rc - 128}")
+        tail = [ln for ln in err.strip().splitlines() if ln.strip()][-1:]
+        return "crash", f"{sig}: {tail[0][:200] if tail else ''}"
+    tail = [ln for ln in err.strip().splitlines() if ln.strip()][-1:]
+    return "crash", f"rc={rc}: {tail[0][:200] if tail else ''}"
+
+
+def norm(msg):
+    m = msg.split("\n")[0]
+    m = re.sub(r"0x[0-9a-fA-F]+", "X", m)
+    m = re.sub(r'"[^"]*"', '"…"', m)
+    m = re.sub(r"'[^']*'", "'…'", m)
+    m = re.sub(r"\d+", "N", m)
+    return m[:160]
+
+
+def panic_head(msg):
+    """First line + first clawhdf5 frame of a PANIC record."""
+    lines = msg.split("\n")
+    frame = next((ln.strip() for ln in lines[1:] if "clawhdf5_format" in ln), "")
+    return lines[0][:300], frame[:300]
+
+
+def eq_shape(a, b):
+    return a == b
+
+
+rows = []
+issues_by_file = {}
+root_causes = collections.defaultdict(lambda: {"files": set(), "count": 0, "examples": []})
+mismatch_causes = collections.defaultdict(lambda: {"files": set(), "count": 0, "examples": []})
+panics = []
+ref_only_errors = collections.Counter()
+incomparable = collections.Counter()
+
+
+def add(bucket, key, file, example):
+    b = bucket[key]
+    b["count"] += 1
+    if file not in b["files"] and len(b["examples"]) < 6:
+        b["examples"].append(example)
+    b["files"].add(file)
+
+
+files = [ln.strip() for ln in open(os.path.join(R, "files.txt")) if ln.strip()]
+for rel in files:
+    d = os.path.join(RUNS, rel.replace("/", "__"))
+    corpus = rel.split("/")[0]
+    ours, ref = load(d, "ours"), load(d, "ref")
+    h5dump = load(d, "h5dump")
+    os_, od = proc_status(ours)
+    rs, rd = proc_status(ref)
+    oj = ours["json"] if ours else None
+    rj = ref["json"] if ref else None
+    issues = []  # (kind, detail)
+    caught_panics = []
+
+    def scan_err(path, what, msg):
+        if msg.startswith("PANIC:"):
+            caught_panics.append((path, what, msg))
+
+    if oj:
+        for o in oj.get("objects", []):
+            for k in ("error", "attrs_error", "list_error"):
+                if k in o:
+                    scan_err(o["path"], k, o[k])
+            for an, av in (o.get("attrs") or {}).items():
+                if "error" in av:
+                    scan_err(o["path"], f"attr {an}", av["error"])
+        if oj.get("open_error", "").startswith("PANIC:"):
+            caught_panics.append(("<open>", "open", oj["open_error"]))
+
+    ref_open_fail = rs != "ok" or (rj is not None and "open_error" in rj)
+    ours_open_err = oj.get("open_error") if oj else None
+    n_obj = n_ok = 0
+    if os_ == "ok" and rj and not ref_open_fail and not ours_open_err:
+        ro = {x["path"]: x for x in rj.get("objects", [])}
+        oo = {x["path"]: x for x in oj.get("objects", [])}
+        our_list_errors = [x for x in oo.values() if "list_error" in x]
+        for p in sorted(set(ro) | set(oo)):
+            a, b = ro.get(p), oo.get(p)
+            n_obj += 1
+            if a is None:
+                issues.append(("mismatch", f"extra object {p} (kind={b.get('kind')})", "extra-object", b))
+                continue
+            if b is None:
+                if our_list_errors:
+                    continue  # accounted for by the list_error
+                issues.append(("mismatch", f"missing object {p} (kind={a.get('kind')})", "missing-object", a))
+                continue
+            ok = True
+            if a.get("kind") != b.get("kind") and "error" not in b and "error" not in a:
+                issues.append(("mismatch", f"{p}: kind {a.get('kind')} vs ours {b.get('kind')}", "kind", b))
+                ok = False
+            for k in ("error", "list_error", "attrs_error"):
+                if k in b and k not in a:
+                    issues.append(("our-error", f"{p}: {k}: {b[k]}", b[k], b))
+                    ok = False
+                elif k in a and k not in b and k == "error":
+                    ref_only_errors[norm(a[k])] += 1
+            if a.get("kind") == "dataset" and "error" not in a and "error" not in b:
+                if "skipped" in a or "skipped" in b:
+                    pass
+                elif a.get("converted"):
+                    incomparable[f"dataset {a['converted']}"] += 1
+                elif a.get("shape") != b.get("shape"):
+                    issues.append(("mismatch", f"{p}: shape {a.get('shape')} vs ours {b.get('shape')}", "shape", b))
+                    ok = False
+                elif a.get("hash") != b.get("hash"):
+                    issues.append(("mismatch", f"{p}: values differ (h5py {a.get('dtype')} vs ours {b.get('dtype')})", "values", b | {"ref_head": a.get("head"), "ref_dtype": a.get("dtype")}))
+                    ok = False
+            ra, oa = a.get("attrs") or {}, b.get("attrs") or {}
+            if "attrs_error" not in b and "attrs_error" not in a:
+                for an in sorted(set(ra) | set(oa)):
+                    x, y = ra.get(an), oa.get(an)
+                    if x is None:
+                        issues.append(("mismatch", f"{p}@{an}: extra attribute", "extra-attr", y or {}))
+                    elif y is None:
+                        issues.append(("mismatch", f"{p}@{an}: missing attribute", "missing-attr", x))
+                    elif "error" in y and "error" not in x:
+                        issues.append(("our-error", f"{p}@{an}: {y['error']}", y["error"], y))
+                    elif "error" in x:
+                        continue
+                    elif x.get("converted"):
+                        incomparable[f"attr {x['converted']}"] += 1
+                    elif x.get("shape") != y.get("shape"):
+                        issues.append(("mismatch", f"{p}@{an}: attr shape {x.get('shape')} vs ours {y.get('shape')}", "attr-shape", y | {"ref_dtype": x.get("dtype")}))
+                    elif x.get("hash") != y.get("hash"):
+                        issues.append(("mismatch", f"{p}@{an}: attr values differ (h5py {x.get('dtype')} vs ours {y.get('dtype')})", "attr-values", y | {"ref_head": x.get("head"), "ref_dtype": x.get("dtype")}))
+            if ok:
+                n_ok += 1
+
+    # classify
+    if os_ in ("hang", "oom", "crash", "panic"):
+        cls = os_
+    elif caught_panics:
+        cls = "panic"
+    elif ref_open_fail:
+        cls = "h5py-cannot-read"
+    elif ours_open_err:
+        cls = "our-error"
+        issues.append(("our-error", f"open: {ours_open_err}", ours_open_err, {}))
+    elif any(i[0] == "our-error" for i in issues):
+        cls = "our-error"
+    elif issues:
+        cls = "mismatch"
+    else:
+        cls = "ok"
+
+    if os_ in ("hang", "oom", "crash", "panic") or caught_panics:
+        panics.append({
+            "file": rel, "class": cls, "detail": od,
+            "stderr": (ours["err"] if ours else "")[:3000],
+            "caught": [(p, w, m[:2500]) for p, w, m in caught_panics[:3]],
+            "n_caught": len(caught_panics),
+        })
+    for kind, detail, key, rec in issues:
+        if kind == "our-error":
+            add(root_causes, norm(key), rel, detail[:300])
+        else:
+            if key in ("values", "attr-values", "shape", "attr-shape"):
+                mk = f"{key}: ours={rec.get('dtype')} h5py={rec.get('ref_dtype')} layout={rec.get('layout','-')} filters={rec.get('filters','-')}"
+            else:
+                mk = key
+            add(mismatch_causes, mk, rel, detail[:300] + (f" | ref_head={rec.get('ref_head')} our_head={rec.get('head')}" if rec.get("ref_head") else ""))
+    ref_detail = rd if rs != "ok" else ((rj or {}).get("open_error") or "")
+    h5d = ""
+    if h5dump:
+        rc = h5dump["rc"]
+        h5d = {0: "ok", 1: "error", 137: "hang", 124: "hang", 134: "SIGABRT", 139: "SIGSEGV", 136: "SIGFPE", 135: "SIGBUS"}.get(rc, f"rc={rc}")
+        if "memory allocation" in h5dump["err"] or "Cannot allocate" in h5dump["err"]:
+            h5d += "(oom)"
+    rows.append({
+        "file": rel, "corpus": corpus, "class": cls,
+        "ours": os_ if os_ != "ok" else ("open-error" if ours_open_err else ("panic" if caught_panics else "ok")),
+        "ours_detail": (od or ours_open_err or (caught_panics[0][2].split("\n")[0] if caught_panics else ""))[:300],
+        "ref": rs if rs != "ok" else ("open-error" if (rj or {}).get("open_error") else "ok"),
+        "ref_detail": ref_detail[:300],
+        "h5dump_1_14_6": h5d,
+        "h5dump_detail": ([ln for ln in h5dump["err"].splitlines() if ln.strip()][-1:] or [""])[0][:200] if h5dump else "",
+        "objects": n_obj, "objects_ok": n_ok,
+        "issues": len(issues), "first_issue": issues[0][1][:300] if issues else "",
+        "superblock": (oj or {}).get("superblock_version", ""),
+    })
+    # the first issues of each file, for report.py's known-cause matching
+    issues_by_file[rel] = [
+        {"kind": k, "key": key, "detail": det[:300], "ours_dtype": rec.get("dtype"), "ref_dtype": rec.get("ref_dtype")}
+        for k, det, key, rec in issues[:50]
+    ]
+
+with open(os.path.join(R, "results.csv"), "w", newline="") as fh:
+    w = csv.DictWriter(fh, fieldnames=list(rows[0].keys()))
+    w.writeheader()
+    w.writerows(rows)
+
+
+def ser(b):
+    return {k: {"files": len(v["files"]), "count": v["count"], "examples": v["examples"], "file_list": sorted(v["files"])} for k, v in sorted(b.items(), key=lambda kv: -len(kv[1]["files"]))}
+
+
+json.dump({"rows": rows, "issues": issues_by_file, "root_causes": ser(root_causes), "mismatch_causes": ser(mismatch_causes),
+           "panics": panics, "incomparable": incomparable.most_common(), "ref_only_errors": ref_only_errors.most_common()},
+          open(os.path.join(R, "results.json"), "w"), indent=1)
+
+classes = ["ok", "our-error", "mismatch", "h5py-cannot-read", "hang", "panic", "crash", "oom"]
+by_corpus = collections.defaultdict(collections.Counter)
+for r in rows:
+    by_corpus[r["corpus"]][r["class"]] += 1
+    by_corpus["ALL"][r["class"]] += 1
+lines = ["# Conformance sweep summary", "", "| corpus | files | " + " | ".join(classes) + " |", "|---" * (len(classes) + 2) + "|"]
+for c in sorted(by_corpus, key=lambda k: (k == "ALL", k)):
+    cnt = by_corpus[c]
+    lines.append(f"| {c} | {sum(cnt.values())} | " + " | ".join(str(cnt.get(k, 0)) for k in classes) + " |")
+lines += ["", "## Panics / hangs / crashes / OOM", ""]
+for p in panics:
+    lines.append(f"- **{p['file']}** [{p['class']}] {p['detail']}")
+    for path, what, m in p["caught"][:1]:
+        lines.append("  ```\n  " + f"{path} ({what}): " + m.replace("\n", "\n  ")[:1500] + "\n  ```")
+    if not p["caught"] and p["stderr"]:
+        lines.append("  ```\n  " + p["stderr"].strip()[:1500].replace("\n", "\n  ") + "\n  ```")
+lines += ["", "## Our-error root causes (files affected)", ""]
+for k, v in ser(root_causes).items():
+    lines.append(f"- [{v['files']} files, {v['count']} objs] `{k}`")
+    for ex in v["examples"][:3]:
+        lines.append(f"    - {ex}")
+lines += ["", "## Mismatch root causes", ""]
+for k, v in ser(mismatch_causes).items():
+    lines.append(f"- [{v['files']} files, {v['count']} objs] `{k}`")
+    for ex in v["examples"][:3]:
+        lines.append(f"    - {ex}")
+lines += ["", "## Objects h5py fails on but we read (top)", ""]
+for k, n in ref_only_errors.most_common(15):
+    lines.append(f"- {n} x `{k}`")
+open(os.path.join(R, "summary.md"), "w").write("\n".join(lines) + "\n")
+print("\n".join(lines[:4 + len(by_corpus)]))

conformance/corpus.txt

@@ -0,0 +1,19 @@
+# Conformance corpora, pinned by commit. fetch-corpus.sh reads this file.
+#
+# name  git-url  commit  root  [sparse-checkout patterns...]
+#
+# `root` is the directory inside the checkout that is swept ("." = all of it).
+# Patterns are git non-cone sparse-checkout patterns; none = whole repository.
+# Every file under <root> with an HDF5/netCDF-4 extension is probed; for
+# cve_hdf5 the extension-less files in cvefiles/ and fuzzerfiles/ are too.
+# Licences: each corpus keeps its upstream licence; nothing here is committed
+# to this repository — the files are downloaded into the gitignored cache.
+hdf5              https://github.com/HDFGroup/hdf5.git            a3cf1ea82cc7a66e50029a688121e1b105a7ce88  .  *.h5 *.he5 *.nc *.hdf5 *.h5f
+cve_hdf5          https://github.com/HDFGroup/cve_hdf5.git        3fd1f5ae3869e01b8ae02b41d7108de7ffb1a374  .
+netcdf-c          https://github.com/Unidata/netcdf-c.git         beb7b9585273c1548386231a59b809d906359033  .  /nc_test4/*.nc /ncdump/*.nc /nc_test4/*.h5 /ncdump/*.h5 /h5_test/*.h5 /hdf5_test/*.h5
+NCAS-CMS_pyfive   https://github.com/NCAS-CMS/pyfive.git          8cf07b8749133f41c5e30b8a4c604486f687fe74  .  *.h5 *.hdf5 *.hdf *.nc *.he5
+usnistgov_h5wasm  https://github.com/usnistgov/h5wasm.git         02f6336527d2812783fcedabfbf42127ec8d06d2  .  *.h5 *.hdf5 *.hdf *.nc *.he5
+netcdf4-python    https://github.com/Unidata/netcdf4-python.git   6e67576d39aef8091fb20bd767b4f1a52ddc1bec  .  *.nc *.h5
+xarray-data       https://github.com/pydata/xarray-data.git       a35297e9da2cc99c811014f0c8a4297345a5c28d  .  /basin_mask.nc /precipitation.nc4 /imerghh_730.hdf5 /eraint_uvz.nc /ROMS_example.nc /tiny.nc
+# h5py 3.16.0 (tag 3.16.0), its test data files.
+h5py_data         https://github.com/h5py/h5py.git                b2f0347c4200333acd89b43733f1caa0c115162f  h5py/tests/data_files  /h5py/tests/data_files/*

conformance/fetch-corpus.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+# fetch-corpus.sh [cache_dir]
+#
+# Download the corpora pinned in conformance/corpus.txt into the (gitignored)
+# cache: <cache>/src/<name> is a shallow, sparse, blob-filtered checkout of the
+# pinned commit and <cache>/corpus/<name> links to the swept root inside it.
+# A corpus already checked out at its pinned commit is left alone, so a second
+# run costs nothing and needs no network.
+set -euo pipefail
+HERE="$(cd "$(dirname "$0")" && pwd)"
+CACHE="${1:-${CONFORMANCE_CACHE:-$HERE/.cache}}"
+mkdir -p "$CACHE/src" "$CACHE/corpus"
+CACHE="$(cd "$CACHE" && pwd)"
+
+retry() { local i; for i in 1 2 3 4; do "$@" && return 0; sleep $((i * 5)); done; return 1; }
+
+grep -v '^[[:space:]]*\(#\|$\)' "$HERE/corpus.txt" | while read -r name url commit root patterns; do
+  src="$CACHE/src/$name"
+  if [ -d "$src/.git" ] && [ "$(git -C "$src" rev-parse HEAD 2>/dev/null)" = "$commit" ]; then
+    echo "cached   $name @ ${commit:0:12}"
+  else
+    echo "fetching $name @ ${commit:0:12} from $url"
+    rm -rf "$src"
+    git init -q "$src"
+    git -C "$src" remote add origin "$url"
+    git -C "$src" config advice.detachedHead false
+    if [ -n "$patterns" ]; then
+      git -C "$src" config core.sparseCheckout true
+      # no-cone patterns (globs); `set -f` keeps the shell from expanding them
+      (set -f; printf '%s\n' $patterns) > "$src/.git/info/sparse-checkout"
+    fi
+    retry git -C "$src" fetch -q --depth 1 --filter=blob:none origin "$commit"
+    retry git -C "$src" checkout -q FETCH_HEAD
+    got="$(git -C "$src" rev-parse HEAD)"
+    [ "$got" = "$commit" ] || { echo "error: $name checked out $got, expected $commit" >&2; exit 1; }
+  fi
+  ln -sfn "$src/$root" "$CACHE/corpus/$name"
+done
+echo "corpus ready in $CACHE/corpus"

conformance/list_files.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+"""list_files.py <corpus_dir>: print the files the sweep probes, one per line,
+as <corpus>/<path> in byte order.
+
+  * every file named *.h5 *.hdf5 *.he5 *.nc *.nc4 *.hdf *.h5f in each corpus,
+    except netCDF classic / 64-bit-offset / CDF5 files (magic "CDF"): they are
+    not HDF5, so neither side can read them and they say nothing;
+  * plus, for cve_hdf5, every file in cvefiles/ and fuzzerfiles/ except
+    .md/.c sources — the reproducers are mostly extension-less, and they are
+    kept whatever their bytes look like (that is their point).
+"""
+import os
+import sys
+
+EXTS = (".h5", ".hdf5", ".he5", ".nc", ".nc4", ".hdf", ".h5f")
+
+
+def walk(top):
+    for dirpath, dirnames, filenames in os.walk(top):
+        dirnames[:] = [d for d in dirnames if d != ".git"]
+        for fn in filenames:
+            p = os.path.join(dirpath, fn)
+            if os.path.isfile(p) and not os.path.islink(p):
+                yield os.path.relpath(p, top)
+
+
+def main(root):
+    out = set()
+    for corpus in sorted(os.listdir(root)):
+        top = os.path.join(root, corpus)
+        if not os.path.isdir(top):
+            continue
+        for rel in walk(top):
+            path = os.path.join(top, rel)
+            if rel.lower().endswith(EXTS):
+                with open(path, "rb") as fh:
+                    if fh.read(3) == b"CDF":
+                        continue
+                out.add(f"{corpus}/{rel}")
+            elif corpus == "cve_hdf5" and rel.split(os.sep)[0] in ("cvefiles", "fuzzerfiles") \
+                    and not rel.endswith((".md", ".c")):
+                out.add(f"{corpus}/{rel}")
+    for f in sorted(out, key=lambda s: s.encode()):
+        print(f)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1])

conformance/probe/Cargo.lock

@@ -0,0 +1,492 @@
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+ "pkg-config",
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conformance/probe/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "conformance-probe"
+version = "0.1.0"
+edition = "2024"
+rust-version = "1.92"
+publish = false
+description = "Walks an HDF5 file with clawhdf5-format and prints a canonical JSON description (see conformance/README.md)"
+
+# Deliberately outside the main workspace: `cargo test --workspace` never
+# builds it, and it links the optional C codecs (zstd, libaec) that the core
+# crates' default build must not.
+[workspace]
+
+[dependencies]
+clawhdf5-format = { path = "../../crates/clawhdf5-format", features = ["lz4", "zstd", "szip", "pcodec", "plugin-filters"] }
+serde_json = "1"
+sha2 = "0.10"
+
+[profile.release]
+# Keep panics catchable (the probe records them per object) and turn integer
+# overflow into a reported panic instead of silent wraparound.
+debug = 1
+overflow-checks = true
+debug-assertions = true
+panic = "unwind"

conformance/probe/src/main.rs

@@ -0,0 +1,885 @@
+//! Conformance probe: walks an HDF5 file with clawhdf5-format (the same calls
+//! the `clawhdf5` facade makes) and prints a canonical JSON description:
+//! every hard-linked object (sorted-name DFS, deduplicated by header address),
+//! and for each dataset / attribute its shape plus the SHA-256 of its values
+//! in a canonical encoding shared with `ref.py`.
+//!
+//! Canonical value encoding (per element, concatenated, row-major):
+//!   int / float / bitfield / enum / time : element bytes, little-endian
+//!   non-IEEE-layout float (e.g. N-Bit)   : the IEEE float of the same size it converts to
+//!   int with bit offset / short precision: the full-width integer it converts to
+//!   opaque                               : raw bytes
+//!   compound                             : members in declaration order (padding dropped)
+//!   array                                : base elements row-major
+//!   string (fixed or VL)                 : b'S' + u32le len + bytes (cut at first NUL, trailing spaces stripped)
+//!   VL sequence                          : b'V' + u32le count + base elements
+//!   reference                            : b'R' (payload not compared)
+//!
+//! Every object is processed inside catch_unwind; a caught panic is recorded
+//! with its message, location and the clawhdf5 frames of its backtrace.
+
+use std::cell::RefCell;
+use std::collections::HashSet;
+use std::panic::{self, AssertUnwindSafe};
+
+use clawhdf5_format::attribute::extract_attributes_full;
+use clawhdf5_format::data_layout::DataLayout;
+use clawhdf5_format::data_read;
+use clawhdf5_format::dataspace::{Dataspace, DataspaceType};
+use clawhdf5_format::datatype::{Datatype, DatatypeByteOrder};
+use clawhdf5_format::filter_pipeline::FilterPipeline;
+use clawhdf5_format::group_v1::{self, GroupEntry};
+use clawhdf5_format::group_v2;
+use clawhdf5_format::message_type::MessageType;
+use clawhdf5_format::object_header::ObjectHeader;
+use clawhdf5_format::signature;
+use clawhdf5_format::superblock::Superblock;
+use clawhdf5_format::symbol_table::SymbolTableMessage;
+use clawhdf5_format::vl_data::{VlResolver, check_element_size};
+use serde_json::{Map, Value, json};
+use sha2::{Digest, Sha256};
+
+const MAX_BYTES: u64 = 200 * 1024 * 1024;
+const MAX_OBJECTS: usize = 200_000;
+
+thread_local! {
+    static LAST_PANIC: RefCell<Option<String>> = const { RefCell::new(None) };
+}
+
+fn install_hook() {
+    panic::set_hook(Box::new(|info| {
+        let msg = if let Some(s) = info.payload().downcast_ref::<&str>() {
+            s.to_string()
+        } else if let Some(s) = info.payload().downcast_ref::<String>() {
+            s.clone()
+        } else {
+            "<non-string panic>".into()
+        };
+        let loc = info
+            .location()
+            .map(|l| format!("{}:{}", l.file(), l.line()))
+            .unwrap_or_default();
+        let bt = std::backtrace::Backtrace::force_capture().to_string();
+        // keep only frames from clawhdf5 code
+        let mut frames = Vec::new();
+        let lines: Vec<&str> = bt.lines().collect();
+        for (i, l) in lines.iter().enumerate() {
+            let t = l.trim();
+            if t.contains("clawhdf5_format::") || t.contains("conformance_probe::") {
+                let at = lines
+                    .get(i + 1)
+                    .map(|n| n.trim())
+                    .filter(|n| n.starts_with("at "))
+                    .map(|n| {
+                        let n = n.trim_start_matches("at ");
+                        match n.find("/crates/") {
+                            Some(p) => n[p + 1..].to_string(),
+                            None => n.to_string(),
+                        }
+                    })
+                    .unwrap_or_default();
+                let name = t.split_once(": ").map(|x| x.1).unwrap_or(t);
+                frames.push(format!("{name} ({at})"));
+                if frames.len() >= 12 {
+                    break;
+                }
+            }
+        }
+        let full = format!("PANIC: {msg} @ {loc}\n  {}", frames.join("\n  "));
+        eprintln!("{full}");
+        LAST_PANIC.with(|p| *p.borrow_mut() = Some(full));
+    }));
+}
+
+/// Run `f`, turning a panic into Err("PANIC: ...").
+fn guarded<T>(f: impl FnOnce() -> Result<T, String>) -> Result<T, String> {
+    match panic::catch_unwind(AssertUnwindSafe(f)) {
+        Ok(r) => r,
+        Err(_) => Err(LAST_PANIC
+            .with(|p| p.borrow_mut().take())
+            .unwrap_or_else(|| "PANIC: <unknown>".into())),
+    }
+}
+
+fn e<E: std::fmt::Debug>(x: E) -> String {
+    format!("{x:?}")
+}
+
+struct Ctx<'a> {
+    data: &'a [u8],
+    os: u8,
+    ls: u8,
+    base_dir: std::path::PathBuf,
+    /// Resolves variable-length elements as the library does (null
+    /// elements, strings cut at a NUL, heap objects of the wrong size
+    /// refused), caching each heap collection.
+    vl: RefCell<VlResolver<'a>>,
+}
+
+impl<'a> Ctx<'a> {
+    fn header(&self, addr: u64) -> Result<ObjectHeader, String> {
+        ObjectHeader::parse(self.data, addr as usize, self.os, self.ls).map_err(e)
+    }
+
+    fn payload(&self, h: &ObjectHeader, t: MessageType) -> Result<Option<Vec<u8>>, String> {
+        match h.messages.iter().find(|m| m.msg_type == t) {
+            None => Ok(None),
+            Some(m) => {
+                clawhdf5_format::shared_message::message_data(self.data, m, self.os, self.ls)
+                    .map(|c| Some(c.into_owned()))
+                    .map_err(e)
+            }
+        }
+    }
+
+    fn canon(&self, dt: &Datatype, b: &[u8], out: &mut Vec<u8>) -> Result<(), String> {
+        let size = dt.type_size() as usize;
+        if b.len() < size {
+            return Err(format!(
+                "canon: element slice {} < type size {size}",
+                b.len()
+            ));
+        }
+        match dt {
+            Datatype::FloatingPoint { .. } if !ieee_layout(dt) => {
+                canon_custom_float(dt, &b[..size], out)?
+            }
+            Datatype::FixedPoint { .. } if partial_int(dt) => {
+                canon_partial_int(dt, &b[..size], out)?
+            }
+            Datatype::FixedPoint { byte_order, .. }
+            | Datatype::BitField { byte_order, .. }
+            | Datatype::FloatingPoint { byte_order, .. } => match byte_order {
+                DatatypeByteOrder::LittleEndian => out.extend_from_slice(&b[..size]),
+                DatatypeByteOrder::BigEndian => out.extend(b[..size].iter().rev()),
+                DatatypeByteOrder::Vax => return Err("canon: VAX byte order".into()),
+            },
+            Datatype::Time { .. } | Datatype::Opaque { .. } => out.extend_from_slice(&b[..size]),
+            Datatype::String { .. } => canon_str(&b[..size], out),
+            Datatype::Compound { members, .. } => {
+                for m in members {
+                    let off = m.byte_offset as usize;
+                    let ms = m.datatype.type_size() as usize;
+                    if off.checked_add(ms).is_none_or(|end| end > size) {
+                        return Err(format!("canon: member {} out of bounds", m.name));
+                    }
+                    self.canon(&m.datatype, &b[off..off + ms], out)?;
+                }
+            }
+            Datatype::Reference { .. } => out.push(b'R'),
+            Datatype::Enumeration { base_type, .. } => self.canon(base_type, b, out)?,
+            Datatype::Array {
+                base_type,
+                dimensions,
+            } => {
+                let n: usize = dimensions.iter().map(|d| *d as usize).product();
+                let bs = base_type.type_size() as usize;
+                for i in 0..n {
+                    self.canon(base_type, &b[i * bs..], out)?;
+                }
+            }
+            Datatype::VariableLength {
+                size: vl_size,
+                is_string,
+                base_type,
+                ..
+            } => {
+                check_element_size(*vl_size, self.os).map_err(e)?;
+                let el = &b[..size];
+                if *is_string {
+                    let s = self.vl.borrow_mut().string_bytes(el).map_err(e)?;
+                    canon_str(&s[0], out);
+                } else {
+                    let bs = base_type.type_size() as usize;
+                    // The borrow ends here: the base type may itself be
+                    // variable-length.
+                    let seq = self.vl.borrow_mut().sequences(el, bs).map_err(e)?;
+                    let seq = &seq[0];
+                    let len = seq.len() / bs;
+                    out.push(b'V');
+                    out.extend_from_slice(&(len as u32).to_le_bytes());
+                    for i in 0..len {
+                        self.canon(base_type, &seq[i * bs..], out)?;
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Returns (shape json, n_elements)
+    fn shape(ds: &Dataspace) -> (Value, u64) {
+        match ds.space_type {
+            DataspaceType::Null => (Value::String("null".into()), 0),
+            DataspaceType::Scalar => (json!([]), 1),
+            DataspaceType::Simple => {
+                let n = ds.dimensions.iter().fold(1u64, |a, d| a.saturating_mul(*d));
+                (json!(ds.dimensions), n)
+            }
+        }
+    }
+
+    fn hash_values(
+        &self,
+        dt: &Datatype,
+        raw: &[u8],
+        n: u64,
+        rec: &mut Map<String, Value>,
+    ) -> Result<(), String> {
+        let size = dt.type_size() as usize;
+        let need = (n as usize).checked_mul(size).ok_or("n*size overflow")?;
+        if raw.len() != need {
+            return Err(format!(
+                "raw length {} != n_elements {n} * type_size {size}",
+                raw.len()
+            ));
+        }
+        let mut canon = Vec::with_capacity(need);
+        for i in 0..n as usize {
+            self.canon(dt, &raw[i * size..(i + 1) * size], &mut canon)?;
+        }
+        let h = Sha256::digest(&canon);
+        rec.insert("hash".into(), Value::String(hex(&h)));
+        rec.insert(
+            "head".into(),
+            Value::String(hex(&canon[..canon.len().min(48)])),
+        );
+        Ok(())
+    }
+
+    /// VDS source files resolve next to the virtual file; like the library,
+    /// refuse absolute paths and `..`.
+    fn vds_resolver(
+        &self,
+    ) -> impl Fn(&str) -> Result<Option<Vec<u8>>, clawhdf5_format::error::FormatError> + use<> {
+        let base = self.base_dir.clone();
+        move |name: &str| {
+            use clawhdf5_format::error::FormatError;
+            let p = std::path::Path::new(name);
+            if p.is_absolute()
+                || p.components()
+                    .any(|c| matches!(c, std::path::Component::ParentDir))
+            {
+                return Err(FormatError::ChunkedReadError(format!("refused {name}")));
+            }
+            match std::fs::read(base.join(p)) {
+                Ok(b) => Ok(Some(b)),
+                Err(err) if err.kind() == std::io::ErrorKind::NotFound => Ok(None),
+                Err(err) => Err(FormatError::ChunkedReadError(err.to_string())),
+            }
+        }
+    }
+
+    fn read_named_datatype(&self, h: &ObjectHeader) -> Result<(), String> {
+        let dtb = self
+            .payload(h, MessageType::Datatype)?
+            .ok_or("MissingMessage(Datatype)")?;
+        Datatype::parse_in_header(&dtb, h.version).map_err(e)?;
+        Ok(())
+    }
+
+    fn read_dataset(&self, h: &ObjectHeader, rec: &mut Map<String, Value>) -> Result<(), String> {
+        let dtb = self
+            .payload(h, MessageType::Datatype)?
+            .ok_or("MissingMessage(Datatype)")?;
+        let (dt, _) = Datatype::parse_in_header(&dtb, h.version).map_err(e)?;
+        rec.insert("dtype".into(), Value::String(dtype_str(&dt)));
+        let dsb = self
+            .payload(h, MessageType::Dataspace)?
+            .ok_or("MissingMessage(Dataspace)")?;
+        let mut ds = Dataspace::parse(&dsb, self.ls).map_err(e)?;
+        // A virtual dataset's extent can come from its sources (unlimited /
+        // printf mappings), as h5py reports it, rather than the stored one.
+        if let Some(lm) = h
+            .messages
+            .iter()
+            .find(|m| m.msg_type == MessageType::DataLayout)
+            && let Ok(dl @ DataLayout::Virtual { .. }) =
+                DataLayout::parse(&lm.data, self.os, self.ls)
+        {
+            let resolver = self.vds_resolver();
+            ds.dimensions = clawhdf5_format::vds::virtual_dataset_extent(
+                self.data,
+                &dl,
+                &ds,
+                self.os,
+                self.ls,
+                Some(&resolver),
+            )
+            .map_err(e)?;
+        }
+        let (shape, n) = Self::shape(&ds);
+        rec.insert("shape".into(), shape);
+        if n.saturating_mul(dt.type_size() as u64) > MAX_BYTES {
+            rec.insert("skipped".into(), Value::String("too large".into()));
+            return Ok(());
+        }
+        let lm = h
+            .messages
+            .iter()
+            .find(|m| m.msg_type == MessageType::DataLayout)
+            .ok_or("MissingMessage(DataLayout)")?;
+        let dl = DataLayout::parse(&lm.data, self.os, self.ls).map_err(e)?;
+        rec.insert(
+            "layout".into(),
+            Value::String(
+                match &dl {
+                    DataLayout::Compact { .. } => "compact",
+                    DataLayout::Contiguous { .. } => "contiguous",
+                    DataLayout::Chunked { .. } => "chunked",
+                    DataLayout::Virtual { .. } => "virtual",
+                }
+                .into(),
+            ),
+        );
+        let pipeline = match self.payload(h, MessageType::FilterPipeline)? {
+            Some(p) => Some(FilterPipeline::parse(&p).map_err(e)?),
+            None => None,
+        };
+        if let Some(p) = &pipeline {
+            rec.insert(
+                "filters".into(),
+                json!(p.filters.iter().map(|f| f.filter_id).collect::<Vec<_>>()),
+            );
+        }
+        let raw = if matches!(dl, DataLayout::Virtual { .. }) {
+            let resolver = self.vds_resolver();
+            let fill = clawhdf5_format::fill_value::dataset_fill_value_in(
+                self.data,
+                &h.messages,
+                self.os,
+                self.ls,
+            )
+            .map_err(e)?;
+            clawhdf5_format::vds::read_virtual_dataset(
+                self.data,
+                &dl,
+                &ds,
+                &dt,
+                fill.as_deref(),
+                self.os,
+                self.ls,
+                Some(&resolver),
+            )
+            .map_err(e)?
+            .data
+        } else {
+            let cache = clawhdf5_format::chunk_cache::ChunkCache::new();
+            clawhdf5_format::fill_value::read_full_with_fill::<clawhdf5_format::error::FormatError>(
+                &h.messages,
+                self.data,
+                &dl,
+                &ds,
+                dt.type_size() as usize,
+                self.os,
+                self.ls,
+                || {
+                    data_read::read_raw_data_cached(
+                        self.data,
+                        &dl,
+                        &ds,
+                        &dt,
+                        pipeline.as_ref(),
+                        self.os,
+                        self.ls,
+                        &cache,
+                    )
+                },
+            )
+            .map_err(e)?
+        };
+        self.hash_values(&dt, &raw, n, rec)
+    }
+
+    fn attrs(&self, h: &ObjectHeader) -> Result<Map<String, Value>, String> {
+        let msgs = extract_attributes_full(self.data, h, self.os, self.ls).map_err(e)?;
+        let mut out = Map::new();
+        for a in &msgs {
+            let r = guarded(|| {
+                let mut rec = Map::new();
+                rec.insert("dtype".into(), Value::String(dtype_str(&a.datatype)));
+                let (shape, n) = Self::shape(&a.dataspace);
+                rec.insert("shape".into(), shape);
+                self.hash_values(&a.datatype, &a.raw_data, n, &mut rec)?;
+                Ok(rec)
+            });
+            let v = match r {
+                Ok(rec) => Value::Object(rec),
+                Err(msg) => json!({ "error": msg }),
+            };
+            out.insert(a.name.clone(), v);
+        }
+        Ok(out)
+    }
+
+    fn entries(&self, h: &ObjectHeader) -> Result<Vec<GroupEntry>, String> {
+        let v1 = h
+            .messages
+            .iter()
+            .find(|m| m.msg_type == MessageType::SymbolTable);
+        if let Some(m) = v1 {
+            let stm = SymbolTableMessage::parse(&m.data, self.os).map_err(e)?;
+            group_v1::resolve_v1_group_entries(self.data, &stm, self.os, self.ls).map_err(e)
+        } else if h
+            .messages
+            .iter()
+            .any(|m| m.msg_type == MessageType::LinkInfo || m.msg_type == MessageType::Link)
+        {
+            group_v2::resolve_v2_group_entries(self.data, h, self.os, self.ls).map_err(e)
+        } else {
+            Ok(Vec::new())
+        }
+    }
+}
+
+/// Element bytes as an unsigned integer (at most 16 bytes), honouring byte order.
+fn element_bits(b: &[u8], byte_order: &DatatypeByteOrder) -> Result<u128, String> {
+    if b.len() > 16 {
+        return Err(format!("canon: {}-byte numeric element", b.len()));
+    }
+    let mut v = 0u128;
+    match byte_order {
+        DatatypeByteOrder::LittleEndian => {
+            for (i, x) in b.iter().enumerate() {
+                v |= u128::from(*x) << (8 * i);
+            }
+        }
+        DatatypeByteOrder::BigEndian => {
+            for x in b {
+                v = (v << 8) | u128::from(*x);
+            }
+        }
+        DatatypeByteOrder::Vax => return Err("canon: VAX byte order".into()),
+    }
+    Ok(v)
+}
+
+fn field(v: u128, pos: u32, len: u32) -> u128 {
+    if len == 0 || pos >= 128 {
+        return 0;
+    }
+    let v = v >> pos;
+    if len >= 128 {
+        v
+    } else {
+        v & ((1u128 << len) - 1)
+    }
+}
+
+/// True when a float's bit fields are exactly IEEE 754 binary16/32/64 for its
+/// size. h5py hands back such a type's bytes untouched; any other layout (an
+/// N-Bit `H5Tset_precision` float, say) is *converted* by libhdf5 into the
+/// numpy float of the same size, so comparing raw bytes would be meaningless.
+fn ieee_layout(dt: &Datatype) -> bool {
+    let Datatype::FloatingPoint {
+        size,
+        bit_offset,
+        bit_precision,
+        exponent_location,
+        exponent_size,
+        mantissa_location,
+        mantissa_size,
+        exponent_bias,
+        ..
+    } = dt
+    else {
+        return true;
+    };
+    let std = match size {
+        2 => (16, 10, 5, 10, 15),
+        4 => (32, 23, 8, 23, 127),
+        8 => (64, 52, 11, 52, 1023),
+        _ => return true, // no same-size numpy float to convert to: compare raw
+    };
+    *bit_offset == 0
+        && (
+            *bit_precision,
+            *exponent_location,
+            *exponent_size,
+            *mantissa_size,
+            *exponent_bias,
+        ) == (std.0, std.1, std.2, std.3, std.4)
+        && *mantissa_location == 0
+}
+
+/// Canonicalise a non-IEEE-layout float the way libhdf5's float->float
+/// conversion presents it to h5py: as the IEEE float of the same size.
+/// Assumes the implied-leading-one normalisation and the sign bit at the top
+/// of the precision (what `H5Tset_precision` produces; the parser does not
+/// keep either field).
+fn canon_custom_float(dt: &Datatype, b: &[u8], out: &mut Vec<u8>) -> Result<(), String> {
+    let Datatype::FloatingPoint {
+        size,
+        byte_order,
+        bit_offset,
+        bit_precision,
+        exponent_location,
+        exponent_size,
+        mantissa_location,
+        mantissa_size,
+        exponent_bias,
+    } = dt
+    else {
+        unreachable!()
+    };
+    let (esize, msize) = (u32::from(*exponent_size), u32::from(*mantissa_size));
+    if esize == 0 || esize > 30 || msize > 64 {
+        return Err(format!("canon: unsupported float layout e{esize} m{msize}"));
+    }
+    let v = element_bits(b, byte_order)?;
+    let sign_pos = (u32::from(*bit_offset) + u32::from(*bit_precision)).saturating_sub(1);
+    let neg = field(v, sign_pos, 1) == 1;
+    let e = field(v, u32::from(*exponent_location), esize) as i64;
+    let m = field(v, u32::from(*mantissa_location), msize);
+    let emax = (1i64 << esize) - 1;
+    let bias = i64::from(*exponent_bias);
+    let mag = if e == emax {
+        if m == 0 { f64::INFINITY } else { f64::NAN }
+    } else if e == 0 {
+        (m as f64) * 2f64.powi((1 - bias - msize as i64) as i32)
+    } else {
+        ((1u128 << msize) as f64 + m as f64) * 2f64.powi((e - bias - msize as i64) as i32)
+    };
+    let x = if neg { -mag } else { mag };
+    match size {
+        2 => out
+            .extend_from_slice(&clawhdf5_format::float16::f32_to_f16_bits(x as f32).to_le_bytes()),
+        4 => out.extend_from_slice(&(x as f32).to_le_bytes()),
+        8 => out.extend_from_slice(&x.to_le_bytes()),
+        _ => unreachable!("ieee_layout keeps other sizes raw"),
+    }
+    Ok(())
+}
+
+/// Integers stored with a bit offset or reduced precision (N-Bit): libhdf5
+/// converts them to the full-width integer of the same size, shifting the
+/// value down and sign-extending from the top precision bit.
+fn canon_partial_int(dt: &Datatype, b: &[u8], out: &mut Vec<u8>) -> Result<(), String> {
+    let Datatype::FixedPoint {
+        size,
+        byte_order,
+        signed,
+        bit_offset,
+        bit_precision,
+    } = dt
+    else {
+        unreachable!()
+    };
+    let prec = u32::from(*bit_precision);
+    let v = element_bits(b, byte_order)?;
+    let mut x = field(v, u32::from(*bit_offset), prec);
+    if *signed && prec > 0 && prec < 128 && field(x, prec - 1, 1) == 1 {
+        x |= !0u128 << prec;
+    }
+    out.extend_from_slice(&x.to_le_bytes()[..*size as usize]);
+    Ok(())
+}
+
+fn partial_int(dt: &Datatype) -> bool {
+    matches!(dt, Datatype::FixedPoint { size, bit_offset, bit_precision, .. }
+        if *bit_offset != 0 || u32::from(*bit_precision) != size * 8)
+}
+
+fn canon_str(b: &[u8], out: &mut Vec<u8>) {
+    let cut = b.iter().position(|&c| c == 0).unwrap_or(b.len());
+    let mut s = &b[..cut];
+    while let [rest @ .., b' '] = s {
+        s = rest;
+    }
+    out.push(b'S');
+    out.extend_from_slice(&(s.len() as u32).to_le_bytes());
+    out.extend_from_slice(s);
+}
+
+fn hex(b: &[u8]) -> String {
+    b.iter().map(|x| format!("{x:02x}")).collect()
+}
+
+fn dtype_str(dt: &Datatype) -> String {
+    match dt {
+        Datatype::FixedPoint {
+            size,
+            signed,
+            byte_order,
+            ..
+        } => {
+            format!(
+                "{}{}{}",
+                bo(byte_order),
+                if *signed { "i" } else { "u" },
+                size
+            )
+        }
+        Datatype::FloatingPoint {
+            size, byte_order, ..
+        } => format!("{}f{}", bo(byte_order), size),
+        Datatype::BitField {
+            size, byte_order, ..
+        } => format!("{}b{}", bo(byte_order), size),
+        Datatype::Time { size, .. } => format!("time{size}"),
+        Datatype::String { size, .. } => format!("S{size}"),
+        Datatype::Opaque { size, .. } => format!("V{size}"),
+        Datatype::Compound { size, members } => format!(
+            "{{{}}}{size}",
+            members
+                .iter()
+                .map(|m| format!("{}:{}", m.name, dtype_str(&m.datatype)))
+                .collect::<Vec<_>>()
+                .join(",")
+        ),
+        Datatype::Reference { ref_type, .. } => format!("ref({ref_type:?})"),
+        Datatype::Enumeration { base_type, .. } => format!("enum({})", dtype_str(base_type)),
+        Datatype::VariableLength {
+            is_string: true, ..
+        } => "vlstr".into(),
+        Datatype::VariableLength { base_type, .. } => format!("vlen({})", dtype_str(base_type)),
+        Datatype::Array {
+            base_type,
+            dimensions,
+        } => format!("({}){dimensions:?}", dtype_str(base_type)),
+    }
+}
+
+fn bo(b: &DatatypeByteOrder) -> &'static str {
+    match b {
+        DatatypeByteOrder::LittleEndian => "<",
+        DatatypeByteOrder::BigEndian => ">",
+        DatatypeByteOrder::Vax => "vax",
+    }
+}
+
+fn is_group(h: &ObjectHeader) -> bool {
+    h.messages.iter().any(|m| {
+        matches!(
+            m.msg_type,
+            MessageType::LinkInfo | MessageType::Link | MessageType::SymbolTable
+        )
+    })
+}
+
+fn main() {
+    install_hook();
+    let path = std::env::args().nth(1).expect("usage: probe <file>");
+    let mut top = Map::new();
+    top.insert("file".into(), Value::String(path.clone()));
+    let data = match std::fs::read(&path) {
+        Ok(d) => d,
+        Err(err) => {
+            top.insert("open_error".into(), Value::String(format!("Io({err})")));
+            println!("{}", Value::Object(top));
+            return;
+        }
+    };
+    // Every address is relative to the superblock: look at the file from
+    // there on (past any user block), as libhdf5 does.
+    let hdf5: &[u8] = match signature::find_signature(&data) {
+        Ok(off) => &data[off..],
+        Err(_) => &data,
+    };
+    let sb = guarded(|| Superblock::parse(hdf5, 0).map_err(e));
+    let sb = match sb {
+        Ok(sb) => sb,
+        Err(msg) => {
+            top.insert("open_error".into(), Value::String(msg));
+            println!("{}", Value::Object(top));
+            return;
+        }
+    };
+    // libhdf5 refuses a truncated file and reads nothing past the recorded
+    // end of file.
+    let base = (data.len() - hdf5.len()) as u64;
+    let hdf5 = match sb.data_end(base, data.len() as u64) {
+        Ok(end) => &hdf5[..end as usize],
+        Err(err) => {
+            top.insert("open_error".into(), Value::String(e(err)));
+            println!("{}", Value::Object(top));
+            return;
+        }
+    };
+    top.insert("superblock_version".into(), json!(sb.version));
+    let ctx = Ctx {
+        data: hdf5,
+        os: sb.offset_size,
+        ls: sb.length_size,
+        base_dir: std::path::Path::new(&path)
+            .parent()
+            .map(|p| p.to_path_buf())
+            .unwrap_or_default(),
+        vl: RefCell::new(VlResolver::new(hdf5, sb.offset_size, sb.length_size)),
+    };
+    let mut objects: Vec<Value> = Vec::new();
+    let mut visited = HashSet::new();
+    let mut soft_v1 = 0u64;
+    // explicit DFS stack: (address, path)
+    let mut stack: Vec<(u64, String)> = vec![(sb.root_group_address, "/".to_string())];
+    while let Some((addr, p)) = stack.pop() {
+        if objects.len() >= MAX_OBJECTS {
+            top.insert("truncated".into(), json!(true));
+            break;
+        }
+        if !visited.insert(addr) {
+            continue;
+        }
+        let mut rec = Map::new();
+        rec.insert("path".into(), Value::String(p.clone()));
+        let r = guarded(|| {
+            let h = ctx.header(addr)?;
+            Ok(h)
+        });
+        let h = match r {
+            Ok(h) => h,
+            Err(msg) => {
+                rec.insert("kind".into(), Value::String("unknown".into()));
+                rec.insert("error".into(), Value::String(msg));
+                objects.push(Value::Object(rec));
+                continue;
+            }
+        };
+        let is_ds = h
+            .messages
+            .iter()
+            .any(|m| m.msg_type == MessageType::DataLayout);
+        let kind = if is_ds {
+            "dataset"
+        } else if is_group(&h) || addr == sb.root_group_address {
+            "group"
+        } else if h
+            .messages
+            .iter()
+            .any(|m| m.msg_type == MessageType::Datatype)
+        {
+            "datatype"
+        } else {
+            "unknown"
+        };
+        rec.insert("kind".into(), Value::String(kind.into()));
+        if kind == "dataset"
+            && let Err(msg) = guarded(|| ctx.read_dataset(&h, &mut rec))
+        {
+            rec.insert("error".into(), Value::String(msg));
+        }
+        // Opening a committed datatype decodes it (h5py's `f[name]` fails on
+        // one libhdf5 cannot decode), so decode it here too.
+        if kind == "datatype"
+            && let Err(msg) = guarded(|| ctx.read_named_datatype(&h))
+        {
+            rec.insert("error".into(), Value::String(msg));
+        }
+        if kind != "datatype" {
+            match guarded(|| ctx.attrs(&h)) {
+                Ok(m) => {
+                    rec.insert("attrs".into(), Value::Object(m));
+                }
+                Err(msg) => {
+                    rec.insert("attrs_error".into(), Value::String(msg));
+                }
+            }
+        }
+        if kind == "group" {
+            match guarded(|| ctx.entries(&h)) {
+                Ok(mut ents) => {
+                    ents.retain(|en| {
+                        if en.cache_type == 2 {
+                            soft_v1 += 1;
+                            false
+                        } else {
+                            true
+                        }
+                    });
+                    ents.sort_by(|a, b| a.name.cmp(&b.name));
+                    let base = if p == "/" { String::new() } else { p.clone() };
+                    for en in ents.into_iter().rev() {
+                        stack.push((en.object_header_address, format!("{base}/{}", en.name)));
+                    }
+                }
+                Err(msg) => {
+                    rec.insert("list_error".into(), Value::String(msg));
+                }
+            }
+        }
+        objects.push(Value::Object(rec));
+    }
+    if soft_v1 > 0 {
+        top.insert("v1_soft_link_entries".into(), json!(soft_v1));
+    }
+    top.insert("objects".into(), Value::Array(objects));
+    println!("{}", Value::Object(top));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// The N-Bit float of libhdf5's `test/testfiles/le_data.h5`
+    /// (`Nbit_float_data_le`): offset 7, precision 20, sign bit 26, exponent
+    /// 20+6 (bias 31), mantissa 7+13.
+    fn nbit_f32(byte_order: DatatypeByteOrder) -> Datatype {
+        Datatype::FloatingPoint {
+            size: 4,
+            byte_order,
+            bit_offset: 7,
+            bit_precision: 20,
+            exponent_location: 20,
+            exponent_size: 6,
+            mantissa_location: 7,
+            mantissa_size: 13,
+            exponent_bias: 31,
+        }
+    }
+
+    fn canon_one(dt: &Datatype, bytes: &[u8]) -> Vec<u8> {
+        let mut out = Vec::new();
+        canon_custom_float(dt, bytes, &mut out).unwrap();
+        out
+    }
+
+    #[test]
+    fn nbit_float_canonicalises_to_the_value_libhdf5_returns() {
+        let le = nbit_f32(DatatypeByteOrder::LittleEndian);
+        let be = nbit_f32(DatatypeByteOrder::BigEndian);
+        assert!(!ieee_layout(&le));
+        // 1.0: exponent = bias, mantissa 0
+        let one: u32 = 31 << 20;
+        assert_eq!(canon_one(&le, &one.to_le_bytes()), 1.0f32.to_le_bytes());
+        assert_eq!(canon_one(&be, &one.to_be_bytes()), 1.0f32.to_le_bytes());
+        // -2.1999512 (h5py's reading of the file's -2.2): sign, e = 32, m = 819
+        let v: u32 = (1 << 26) | (32 << 20) | (819 << 7);
+        assert_eq!(
+            canon_one(&le, &v.to_le_bytes()),
+            (-2.199_951_2f32).to_le_bytes()
+        );
+        assert_eq!(canon_one(&le, &[0; 4]), 0.0f32.to_le_bytes());
+    }
+
+    #[test]
+    fn ieee_floats_keep_their_raw_bytes() {
+        let f32le = Datatype::FloatingPoint {
+            size: 4,
+            byte_order: DatatypeByteOrder::LittleEndian,
+            bit_offset: 0,
+            bit_precision: 32,
+            exponent_location: 23,
+            exponent_size: 8,
+            mantissa_location: 0,
+            mantissa_size: 23,
+            exponent_bias: 127,
+        };
+        assert!(ieee_layout(&f32le));
+    }
+
+    #[test]
+    fn partial_precision_int_is_shifted_and_sign_extended() {
+        let dt = Datatype::FixedPoint {
+            size: 4,
+            byte_order: DatatypeByteOrder::BigEndian,
+            signed: true,
+            bit_offset: 4,
+            bit_precision: 17,
+        };
+        assert!(partial_int(&dt));
+        let stored = (((-5i32) as u32) & 0x1_FFFF) << 4;
+        let mut out = Vec::new();
+        canon_partial_int(&dt, &stored.to_be_bytes(), &mut out).unwrap();
+        assert_eq!(out, (-5i32).to_le_bytes());
+    }
+}

conformance/ref.py

@@ -0,0 +1,259 @@
+#!/usr/bin/env python3
+"""Reference probe: same JSON as the Rust `conformance-probe`, produced with h5py.
+
+Walk: iterative DFS from '/', children in sorted (UTF-8 byte) name order, hard
+links only, each object once (first path wins, deduplicated by object identity).
+Canonical value encoding: see harness/src/main.rs.
+"""
+import hashlib
+import json
+import os
+import struct
+import sys
+
+import numpy as np
+import h5py
+
+try:
+    import hdf5plugin  # noqa: F401  registers blosc/lz4/zstd/bzip2/... filters
+except Exception:  # pragma: no cover
+    pass
+
+MAX_BYTES = 200 * 1024 * 1024
+MAX_OBJECTS = 200_000
+
+
+def canon_str(b, out):
+    if isinstance(b, str):
+        b = b.encode("utf-8", "surrogateescape")
+    b = bytes(b)
+    cut = b.find(b"\x00")
+    if cut >= 0:
+        b = b[:cut]
+    b = b.rstrip(b" ")
+    out += b"S" + struct.pack("<I", len(b)) + b
+
+
+def simple(dt):
+    if dt.fields:
+        return all(simple(dt.fields[n][0]) for n in dt.names)
+    if dt.subdtype:
+        return simple(dt.subdtype[0])
+    return dt.kind in "iufcbV"
+
+
+def packed(dt):
+    if dt.fields:
+        return np.dtype([(n, packed(dt.fields[n][0])) for n in dt.names])
+    if dt.subdtype:
+        base, shape = dt.subdtype
+        return np.dtype((packed(base), shape))
+    if dt.kind in "iufcb":
+        return dt.newbyteorder("<")
+    return dt
+
+
+def canon_el(dt, val, out):
+    if dt.fields:
+        for n in dt.names:
+            canon_el(dt.fields[n][0], val[n], out)
+        return
+    if dt.subdtype:
+        base, _ = dt.subdtype
+        for x in np.asarray(val).reshape(-1):
+            canon_el(base, x, out)
+        return
+    k = dt.kind
+    if k in "iufcb":
+        out += np.asarray(val, dtype=dt).astype(dt.newbyteorder("<")).tobytes()
+    elif k == "V":
+        out += np.asarray(val, dtype=dt).tobytes()
+    elif k == "S":
+        canon_str(val, out)
+    elif k == "O":
+        if h5py.check_string_dtype(dt) is not None:
+            canon_str(val if val is not None else b"", out)
+        elif h5py.check_ref_dtype(dt) is not None:
+            out += b"R"
+        else:
+            base = h5py.check_vlen_dtype(dt)
+            if base is None:
+                raise TypeError(f"unhandled object dtype {dt!r}")
+            arr = np.asarray(val if val is not None else [], dtype=base).reshape(-1)
+            out += b"V" + struct.pack("<I", arr.shape[0])
+            if simple(base):
+                out += arr.astype(packed(base)).tobytes()
+            else:
+                for x in arr:
+                    canon_el(base, x, out)
+    elif k == "U":
+        canon_str(str(val), out)
+    else:
+        raise TypeError(f"unhandled dtype kind {k} ({dt!r})")
+
+
+def has_obj(dt):
+    if dt.fields:
+        return any(has_obj(dt.fields[n][0]) for n in dt.names)
+    if dt.subdtype:
+        return has_obj(dt.subdtype[0])
+    return dt.kind == "O"
+
+
+def note_conversion(tid, dt, rec):
+    """h5py converts some file types (FP8, bfloat16, x87 long double, ...) to a
+    different-sized numpy type; then value bytes are not comparable."""
+    try:
+        if not has_obj(dt) and tid.get_size() != dt.itemsize:
+            rec["converted"] = f"file type size {tid.get_size()} -> numpy {dt} ({dt.itemsize})"
+    except Exception:  # noqa: BLE001
+        pass
+
+
+def hash_values(arr, dt, rec):
+    if dt.subdtype is not None:
+        # h5py expands an HDF5 array element type into trailing array dims
+        dt = dt.subdtype[0]
+    arr = np.asarray(arr, dtype=dt)
+    if simple(dt):
+        c = np.ascontiguousarray(arr).astype(packed(dt)).tobytes()
+    else:
+        out = bytearray()
+        for x in arr.reshape(-1):
+            canon_el(dt, x, out)
+        c = bytes(out)
+    rec["hash"] = hashlib.sha256(c).hexdigest()
+    rec["head"] = c[:48].hex()
+
+
+def err(e):
+    s = f"{type(e).__name__}: {e}"
+    return s.splitlines()[0][:400] if s else type(e).__name__
+
+
+def shape_of(s):
+    return "null" if s is None else list(s)
+
+
+def n_bytes(shape, tid):
+    n = 1
+    for d in shape or ():
+        n *= d
+    return n * tid.get_size()
+
+
+def read_attrs(obj):
+    out = {}
+    names = sorted(obj.attrs.keys(), key=lambda s: s.encode("utf-8", "surrogateescape"))
+    for name in names:
+        rec = {}
+        try:
+            aid = obj.attrs.get_id(name)
+            rec["dtype"] = str(aid.dtype)
+            rec["shape"] = shape_of(aid.shape)
+            note_conversion(aid.get_type(), aid.dtype, rec)
+            if aid.shape is None:
+                hash_values(np.empty((0,), dtype=aid.dtype), aid.dtype, rec)
+            else:
+                val = obj.attrs[name]
+                hash_values(val, aid.dtype, rec)
+        except Exception as e:  # noqa: BLE001
+            rec = {"error": err(e)}
+        out[name] = rec
+    return out
+
+
+def main(path):
+    top = {"file": path}
+    try:
+        f = h5py.File(path, "r")
+    except Exception as e:  # noqa: BLE001
+        top["open_error"] = err(e)
+        print(json.dumps(top))
+        return
+    objects = []
+    seen = set()
+    stack = [("/", None)]
+    while stack:
+        p, obj = stack.pop()
+        if len(objects) >= MAX_OBJECTS:
+            top["truncated"] = True
+            break
+        rec = {"path": p}
+        try:
+            if obj is None:
+                obj = f[p]
+            key = hash(obj.id)  # h5py ObjectID hash = (fileno, object address/token)
+        except Exception as e:  # noqa: BLE001
+            rec["kind"] = "unknown"
+            rec["error"] = err(e)
+            objects.append(rec)
+            continue
+        if key in seen:
+            continue
+        seen.add(key)
+        if isinstance(obj, h5py.Dataset):
+            kind = "dataset"
+        elif isinstance(obj, h5py.Group):
+            kind = "group"
+        elif isinstance(obj, h5py.Datatype):
+            kind = "datatype"
+        else:
+            kind = "unknown"
+        rec["kind"] = kind
+        if kind == "dataset":
+            try:
+                dt = obj.dtype
+                rec["dtype"] = str(dt)
+                rec["shape"] = shape_of(obj.shape)
+                note_conversion(obj.id.get_type(), dt, rec)
+                if obj.shape is None:
+                    hash_values(np.empty((0,), dtype=dt), dt, rec)
+                elif n_bytes(obj.shape, obj.id.get_type()) > MAX_BYTES:
+                    rec["skipped"] = "too large"
+                else:
+                    arr = np.empty(obj.shape, dtype=dt)
+                    if arr.size:
+                        try:
+                            obj.read_direct(arr)
+                        except Exception:  # noqa: BLE001
+                            arr = obj[()]
+                    hash_values(arr, dt, rec)
+            except Exception as e:  # noqa: BLE001
+                rec["error"] = err(e)
+        if kind != "datatype":
+            try:
+                rec["attrs"] = read_attrs(obj)
+            except Exception as e:  # noqa: BLE001
+                rec["attrs_error"] = err(e)
+        if kind == "group":
+            try:
+                names = sorted(obj.keys(), key=lambda s: s.encode("utf-8", "surrogateescape"))
+                base = "" if p == "/" else p
+                kids = []
+                for n in names:
+                    try:
+                        link = obj.get(n, getlink=True)
+                    except Exception:  # noqa: BLE001
+                        link = None
+                    if link is not None and not isinstance(link, h5py.HardLink):
+                        continue
+                    kids.append(f"{base}/{n}")
+                for k in reversed(kids):
+                    stack.append((k, None))
+            except Exception as e:  # noqa: BLE001
+                rec["list_error"] = err(e)
+        objects.append(rec)
+    top["objects"] = objects
+    print(json.dumps(top), flush=True)
+    # Exit without tearing down the h5py objects: freeing them for some files
+    # that hold references (hdf5's h5repack_attr_refs.h5, cve-2024-32623.h5)
+    # makes libhdf5 2.0 abort with "free(): chunks in smallbin corrupted"
+    # about half the time. That happens after the reading is done, so it says
+    # nothing about what h5py read, but it flipped those files between ok and
+    # h5py-cannot-read from one run to the next.
+    os._exit(0)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1])

conformance/report.py

@@ -0,0 +1,335 @@
+#!/usr/bin/env python3
+"""report.py <results_dir> <CONFORMANCE.md> <corpus_dir>
+
+Render the sweep's results (compare.py's results.json plus the raw per-side
+runs) as CONFORMANCE.md, and write <results_dir>/report-meta.json (commit,
+date, versions) for check.py --update.
+"""
+import collections
+import datetime
+import json
+import os
+import platform
+
+import subprocess
+import sys
+
+import h5py
+import numpy
+
+try:
+    import hdf5plugin
+    HDF5PLUGIN = hdf5plugin.version
+except Exception:  # noqa: BLE001
+    HDF5PLUGIN = "not installed"
+
+R, OUT_MD, CORPUS = sys.argv[1], sys.argv[2], sys.argv[3]
+HERE = os.path.dirname(os.path.abspath(__file__))
+ROOT = os.path.dirname(HERE)
+CLASSES = ["ok", "our-error", "mismatch", "h5py-cannot-read", "panic", "hang", "crash", "oom"]
+
+
+def sh(*cmd, cwd=ROOT):
+    try:
+        return subprocess.run(cmd, cwd=cwd, capture_output=True, text=True, timeout=30).stdout.strip()
+    except Exception:  # noqa: BLE001
+        return ""
+
+
+def cpu_model():
+    try:
+        for ln in open("/proc/cpuinfo"):
+            if ln.startswith(("model name", "Model")):
+                return ln.split(":", 1)[1].strip()
+    except OSError:
+        pass
+    return platform.processor() or "unknown"
+
+
+def mem_gib():
+    try:
+        for ln in open("/proc/meminfo"):
+            if ln.startswith("MemTotal:"):
+                return f"{int(ln.split()[1]) / 1048576:.0f} GiB"
+    except OSError:
+        pass
+    return "?"
+
+
+res = json.load(open(os.path.join(R, "results.json")))
+meta_run = json.load(open(os.path.join(R, "meta.json"))) if os.path.exists(os.path.join(R, "meta.json")) else {}
+rows = res["rows"]
+issues = res.get("issues", {})
+
+# safe.directory: a checkout owned by another user (a container) is still ours to read
+commit = sh("git", "-c", "safe.directory=*", "rev-parse", "HEAD") or os.environ.get("GITHUB_SHA", "unknown")
+lib_dirty = sh("git", "-c", "safe.directory=*", "status", "--porcelain", "--", "crates", "Cargo.toml")
+h5dump_v = sh("h5dump", "--version").replace("h5dump: ", "")
+meta = {
+    "date": datetime.datetime.now(datetime.timezone.utc).strftime("%Y-%m-%d %H:%M UTC"),
+    "commit": commit + (" (library sources modified)" if lib_dirty else ""),
+    "reference": f"h5py {h5py.__version__} / HDF5 {h5py.version.hdf5_version}",
+}
+json.dump(meta, open(os.path.join(R, "report-meta.json"), "w"), indent=1)
+
+pins = []
+for ln in open(os.path.join(HERE, "corpus.txt")):
+    if ln.strip() and not ln.lstrip().startswith("#"):
+        name, url, rev, root, *_ = ln.split()
+        pins.append((name, url, rev, root))
+
+by_corpus = collections.defaultdict(collections.Counter)
+for r in rows:
+    by_corpus[r["corpus"]][r["class"]] += 1
+total = collections.Counter(r["class"] for r in rows)
+
+
+def ex_list(files, n=3):
+    s = ", ".join(f"`{f}`" for f in files[:n])
+    return s + (f" (+{len(files) - n} more)" if len(files) > n else "")
+
+
+# --- known causes that are not clawhdf5 bugs --------------------------------
+def is_h5py_be_vlen(i):
+    """h5py returns the elements of a VL sequence of a big-endian base type
+    with their file (big-endian) bytes but a native-endian dtype."""
+    return (i["kind"] == "mismatch" and i["key"] in ("values", "attr-values")
+            and (i.get("ref_dtype") == "object") and (i.get("ours_dtype") or "").startswith("vlen(")
+            and ">" in (i.get("ours_dtype") or ""))
+
+
+known = collections.defaultdict(list)
+for r in rows:
+    if r["class"] != "mismatch":
+        continue
+    iss = issues.get(r["file"], [])
+    if iss and all(is_h5py_be_vlen(i) for i in iss):
+        known["h5py-be-vlen"].append(r["file"])
+
+
+# --- the CVE corpus: clawhdf5 vs h5dump vs h5py ------------------------------
+def side(run, name):
+    p = os.path.join(R, "runs", run, name)
+    if not os.path.exists(p + ".rc"):
+        return None
+    rc = int(open(p + ".rc").read().strip() or -1)
+    err = open(p + ".err", errors="replace").read()
+    try:
+        j = json.load(open(p + ".json"))
+    except Exception:  # noqa: BLE001
+        j = None
+    return rc, err, j
+
+
+def outcome(s, rust=False):
+    """-> (bucket, text). bucket in read / error / panic / crash / hang / oom."""
+    if s is None:
+        return "missing", "not run"
+    rc, err, j = s
+    if rc in (137, 124):
+        return "hang", "hang (killed at timeout)"
+    if "memory allocation of" in err or "MemoryError" in err or "bad_alloc" in err or "Cannot allocate" in err:
+        return "oom", "out of memory"
+    if rust and (rc == 101 or "PANIC:" in err):
+        return "panic", "panic"
+    if "overflowed its stack" in err:
+        return "crash", "stack overflow"
+    if rc == 139:
+        return "crash", "SIGSEGV"
+    if rc == 134:
+        return "crash", "SIGABRT" + (" (heap corruption)" if ("corrupted" in err or "free()" in err) else "")
+    if rc > 128:
+        return "crash", f"signal {rc - 128}"
+    if j is None:
+        return ("error", "error exit") if rc in (0, 1) else ("crash", f"exit {rc}")
+    if "open_error" in j:
+        return "error", "open error"
+    objs = j.get("objects", [])
+    ne = sum(1 for o in objs for k in ("error", "attrs_error", "list_error") if k in o)
+    ne += sum(1 for o in objs for a in (o.get("attrs") or {}).values() if "error" in a)
+    return "read", f"read {len(objs)} obj" + (f", {ne} errors" if ne else "")
+
+
+def h5dump_outcome(s):
+    if s is None:
+        return "missing", "not run"
+    rc, err, _ = s
+    if rc in (137, 124):
+        return "hang", "hang (killed at timeout)"
+    if "memory allocation" in err or "Cannot allocate" in err:
+        return "oom", "out of memory"
+    if rc == 139:
+        return "crash", "SIGSEGV"
+    if rc == 134:
+        return "crash", "SIGABRT" + (" (heap corruption)" if ("corrupted" in err or "free()" in err) else "")
+    if rc > 128:
+        return "crash", f"signal {rc - 128}"
+    return ("read", "ok") if rc == 0 else ("error", "error exit")
+
+
+cve_rows = []
+buckets = {"clawhdf5": collections.Counter(), "h5dump": collections.Counter(), "h5py": collections.Counter()}
+ours_panic = {r["file"] for r in rows if r["class"] == "panic"}
+for r in rows:
+    if r["corpus"] != "cve_hdf5":
+        continue
+    run = r["file"].replace("/", "__")
+    o = outcome(side(run, "ours"), rust=True)
+    if o[0] == "read" and r["file"] in ours_panic:
+        o = ("panic", "caught panic")
+    p = outcome(side(run, "ref"))
+    d = h5dump_outcome(side(run, "h5dump"))
+    buckets["clawhdf5"][o[0]] += 1
+    buckets["h5py"][p[0]] += 1
+    buckets["h5dump"][d[0]] += 1
+    cve_rows.append((r["file"].split("/", 1)[1], d[1], p[1], o[1], r["class"]))
+
+# --- render -----------------------------------------------------------------
+L = []
+w = L.append
+w("# clawhdf5 conformance report")
+w("")
+w("Every HDF5 file of eight public corpora (pinned by commit) is read twice — by")
+w("clawhdf5 (`conformance/probe`, the same `clawhdf5-format` calls the facade")
+w("makes) and by h5py/libhdf5 (`conformance/ref.py`) — and the two readings are")
+w("compared object by object: the set of hard-linked objects, each dataset's and")
+w("attribute's shape, and a SHA-256 of its values in a canonical encoding. The")
+w("CVE corpus is also run through `h5dump`. Each side runs under a timeout and an")
+w("address-space limit, so a hang, crash or runaway allocation is recorded, not")
+w("fatal. This file is generated by `conformance/run.sh`; do not edit it by hand.")
+w("")
+w("## Run")
+w("")
+w("| | |")
+w("|---|---|")
+w(f"| date | {meta['date']} |")
+w(f"| clawhdf5 commit | `{meta['commit']}` |")
+w(f"| machine | `{platform.node()}`: {cpu_model()}, {os.cpu_count()} CPUs, {mem_gib()}, {platform.system()} {platform.release()} {platform.machine()} |")
+w(f"| command | `{os.environ.get('CONFORMANCE_CMD', 'conformance/run.sh')}` |")
+w(f"| rustc | {sh('rustc', '-V')} |")
+w(f"| reference | h5py {h5py.__version__}, HDF5 {h5py.version.hdf5_version}, numpy {numpy.__version__}, hdf5plugin {HDF5PLUGIN}, Python {platform.python_version()} |")
+w(f"| h5dump | {h5dump_v} (CVE corpus only) |")
+if meta_run:
+    w(f"| limits | {meta_run.get('timeout_s')} s timeout (SIGKILL), {int(meta_run.get('mem_kb', 0)) // 1024} MiB address space, per process; {meta_run.get('jobs')} files in parallel |")
+    w(f"| runtime | {meta_run.get('probe_seconds')} s probing + comparing ({meta_run.get('build_seconds')} s fetch/build before it) |")
+w("")
+w("## Results")
+w("")
+w("A file's class is the first that applies:")
+w("")
+w("- **panic / hang / crash / oom** — clawhdf5 panicked (caught per object or not), hit the timeout, died on a signal, or failed an allocation. The CI gate fails on any of these.")
+w("- **h5py-cannot-read** — libhdf5 could not open the file (or itself crashed or hung). Nothing to compare against; most are the deliberately malformed CVE reproducers.")
+w("- **our-error** — clawhdf5 returned an error for something h5py reads.")
+w("- **mismatch** — both read it, but the shapes, values, object set or attribute set differ.")
+w("- **ok** — every object h5py reads, clawhdf5 reads identically.")
+w("")
+w("| corpus | files | " + " | ".join(CLASSES) + " |")
+w("|---" * (len(CLASSES) + 2) + "|")
+for c in sorted(by_corpus):
+    cnt = by_corpus[c]
+    w(f"| {c} | {sum(cnt.values())} | " + " | ".join(str(cnt.get(k, 0)) for k in CLASSES) + " |")
+w(f"| **all** | **{len(rows)}** | " + " | ".join(f"**{total.get(k, 0)}**" for k in CLASSES) + " |")
+w("")
+n_known = sum(len(v) for v in known.values())
+if n_known:
+    w(f"{n_known} of the {total.get('mismatch', 0)} mismatches are a known h5py bug, not ours (see *Known not-our-bug*).")
+    w("")
+w("Corpora (fetched by `conformance/fetch-corpus.sh` into the gitignored `conformance/.cache/`):")
+w("")
+w("| corpus | source | commit |")
+w("|---|---|---|")
+for name, url, rev, root in pins:
+    w(f"| {name} | {url.removesuffix('.git')}" + ("" if root == "." else f" (`{root}`)") + f" | `{rev[:12]}` |")
+w("")
+
+w("## Panics, hangs, crashes, out-of-memory")
+w("")
+if not res["panics"]:
+    w("None.")
+else:
+    for p in res["panics"]:
+        w(f"- `{p['file']}` [{p['class']}] {p['detail']}")
+w("")
+
+w("## Our-error root causes")
+w("")
+w("Grouped by normalised error message. *files* counts files whose class this cause affects.")
+w("")
+w("| files | objects | error | examples |")
+w("|---:|---:|---|---|")
+for k, v in res["root_causes"].items():
+    w(f"| {v['files']} | {v['count']} | `{k.replace('|', '/')}` | {ex_list(v['file_list'])} |")
+w("")
+w("## Mismatch root causes")
+w("")
+w("| files | objects | cause | examples |")
+w("|---:|---:|---|---|")
+for k, v in res["mismatch_causes"].items():
+    w(f"| {v['files']} | {v['count']} | `{k.replace('|', '/')}` | {ex_list(v['file_list'])} |")
+w("")
+
+w("## CVE corpus: clawhdf5 vs h5dump vs h5py")
+w("")
+w(f"The {len(cve_rows)} files of [HDFGroup/cve_hdf5](https://github.com/HDFGroup/cve_hdf5) — reproducers for")
+w("published libhdf5 CVEs and fuzzer finds. *read* = produced output (possibly with per-object")
+w("errors), *error* = refused cleanly. h5dump exits non-zero on any error anywhere in a file, so")
+w("its read/error split is not comparable with the other two rows; the panic, crash, hang and oom")
+w("columns are.")
+w("")
+w("| tool | read | error | panic | crash | hang | oom |")
+w("|---|---:|---:|---:|---:|---:|---:|")
+for tool, label in (("clawhdf5", "clawhdf5"), ("h5dump", f"h5dump {h5dump_v.split()[-1] if h5dump_v else ''}"),
+                    ("h5py", f"h5py {h5py.__version__} / HDF5 {h5py.version.hdf5_version}")):
+    b = buckets[tool]
+    w(f"| {label} | " + " | ".join(str(b.get(k, 0)) for k in ("read", "error", "panic", "crash", "hang", "oom")) + " |")
+w("")
+w("<details><summary>Per-file outcomes</summary>")
+w("")
+w("| file | h5dump | h5py | clawhdf5 | class |")
+w("|---|---|---|---|---|")
+for f, d, p, o, cls in cve_rows:
+    w(f"| {f} | {d} | {p} | {o} | {cls} |")
+w("")
+w("</details>")
+w("")
+
+w("## Known not-our-bug")
+w("")
+w("- **h5py big-endian variable-length sequences.** h5py returns the elements of a VL sequence")
+w("  whose base type is big-endian with the file's big-endian bytes but a native (little-endian)")
+w("  numpy dtype, so the values it reports are byte-swapped garbage; `h5dump` prints the values")
+w("  clawhdf5 reads. Reproducer: `h5py.vlen_dtype(np.dtype('>f4'))` dataset holding `[1.0, 2.0]`")
+w("  reads back in h5py as `[4.6e-41, 9.0e-44]`. Affected here: "
+  + (ex_list(sorted(known["h5py-be-vlen"]), 10) if known["h5py-be-vlen"] else "none") + ".")
+w("- **Non-IEEE floats and partial-precision integers (N-Bit).** libhdf5 converts a float whose")
+w("  bit layout is not IEEE (e.g. `H5Tset_precision` for the N-Bit filter) or an integer with a")
+w("  bit offset / reduced precision into the plain numpy type of the same size. The probe")
+w("  compares such values as converted numbers, not raw file bytes (before 2026-09-25 it compared")
+w("  raw bytes, which reported every N-Bit float dataset as a mismatch).")
+if res["incomparable"]:
+    w("- **Types h5py widens.** Where h5py reads a type into a numpy type of a different size")
+    w("  (FP8 -> float16, bfloat16 -> float32, x87 long double -> float128) the values are not")
+    w("  compared (shape and presence still are): "
+      + ", ".join(f"{k} ({n}x)" for k, n in res["incomparable"]) + ".")
+w("- **References** are compared by presence only (`R`), not by target.")
+w("")
+if res.get("ref_only_errors"):
+    w("## Objects h5py fails on but clawhdf5 reads")
+    w("")
+    for k, n in res["ref_only_errors"][:15]:
+        w(f"- {n} x `{k}`")
+    w("")
+w("## Reproduce")
+w("")
+w("```sh")
+w("# needs: Rust, python3 with h5py numpy hdf5plugin (conformance/requirements.txt), h5dump (hdf5-tools), git")
+w("CLAWHDF5_PYTHON=/path/to/venv/bin/python conformance/run.sh")
+w("```")
+w("")
+w("The corpus (about 450 MB of sparse checkouts) is cached in `conformance/.cache/`; results for")
+w("every file, both sides' raw JSON and stderr, are in `conformance/.cache/results/`.")
+w("`conformance/baseline.json` holds the ok files the nightly CI job (`.gitea/workflows/conformance.yml`)")
+w("must keep; `conformance/run.sh --update-baseline` rewrites it.")
+
+with open(OUT_MD, "w") as fh:
+    fh.write("\n".join(L) + "\n")

conformance/requirements.txt

@@ -0,0 +1,6 @@
+# The reference side of the conformance sweep. Pinned so the nightly job and a
+# local run compare against the same libhdf5 (h5py wheels bundle it).
+h5py==3.16.0
+numpy==2.5.3
+hdf5plugin==7.1.0
+netCDF4==1.7.4

conformance/run.sh

@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+# conformance/run.sh — the clawhdf5 conformance sweep, end to end.
+#
+#   fetch the pinned corpora (cached) -> build the probe -> probe every file
+#   with clawhdf5 and with h5py (and h5dump for the CVE corpus), each under a
+#   timeout and a memory limit -> compare -> write CONFORMANCE.md -> check the
+#   result against conformance/baseline.json.
+#
+# Usage: conformance/run.sh [--no-fetch] [--no-report] [--update-baseline]
+#
+# Environment:
+#   CLAWHDF5_PYTHON    python with h5py, numpy, hdf5plugin (default: repo .venv, then python3)
+#   CONFORMANCE_CACHE  corpus / build / results cache (default: conformance/.cache)
+#   CONFORMANCE_OUT    results directory (default: $CONFORMANCE_CACHE/results)
+#   CONFORMANCE_REPORT report path (default: CONFORMANCE.md at the repo root)
+#   JOBS               parallel files (default: nproc)
+#   CONFORMANCE_PROBE  use this prebuilt probe binary instead of building one
+#   TMO / MEM_KB       per-process timeout in seconds (20) / address-space limit in KiB (4 GiB)
+#
+# Exit status: 0 = gate passed; 1 = a panic/hang/crash/oom in clawhdf5, or the
+# ok count fell below the baseline, or a baseline-ok file regressed; 2 = setup error.
+set -euo pipefail
+HERE="$(cd "$(dirname "$0")" && pwd)"
+ROOT="$(cd "$HERE/.." && pwd)"
+FETCH=1 REPORT=1 UPDATE=0
+for a in "$@"; do
+  case "$a" in
+    --no-fetch) FETCH=0 ;;
+    --no-report) REPORT=0 ;;
+    --update-baseline) UPDATE=1 ;;
+    -h|--help) sed -n '2,23p' "$0"; exit 0 ;;
+    *) echo "unknown argument: $a" >&2; exit 2 ;;
+  esac
+done
+
+export PATH="$HOME/.cargo/bin:$PATH"
+CACHE="${CONFORMANCE_CACHE:-$HERE/.cache}"
+mkdir -p "$CACHE"; CACHE="$(cd "$CACHE" && pwd)"
+OUT="${CONFORMANCE_OUT:-$CACHE/results}"
+REPORT_PATH="${CONFORMANCE_REPORT:-$ROOT/CONFORMANCE.md}"
+JOBS="${JOBS:-$(nproc 2>/dev/null || echo 4)}"
+if [ -n "${CLAWHDF5_PYTHON:-}" ]; then PY="$CLAWHDF5_PYTHON"
+elif [ -x "$ROOT/.venv/bin/python" ]; then PY="$ROOT/.venv/bin/python"
+else PY="$(command -v python3)"; fi
+export PY TMO="${TMO:-20}" MEM_KB="${MEM_KB:-4194304}"
+command -v h5dump >/dev/null || { echo "error: h5dump not found (install hdf5-tools)" >&2; exit 2; }
+"$PY" -c 'import h5py, numpy, hdf5plugin' || { echo "error: $PY lacks h5py/numpy/hdf5plugin" >&2; exit 2; }
+
+t0=$(date +%s)
+[ "$FETCH" = 1 ] && bash "$HERE/fetch-corpus.sh" "$CACHE"
+C="$CACHE/corpus"
+[ -d "$C" ] || { echo "error: no corpus in $C (run without --no-fetch)" >&2; exit 2; }
+
+if [ -n "${CONFORMANCE_PROBE:-}" ]; then
+  export PROBE="$CONFORMANCE_PROBE"   # a prebuilt probe, e.g. an older one for a before/after
+else
+  echo "== building the probe"
+  CARGO_TARGET_DIR="${CARGO_TARGET_DIR:-$CACHE/target}" \
+    cargo build -q --release --manifest-path "$HERE/probe/Cargo.toml"
+  export PROBE="${CARGO_TARGET_DIR:-$CACHE/target}/release/conformance-probe"
+fi
+t1=$(date +%s)
+
+rm -rf "$OUT"; mkdir -p "$OUT"
+"$PY" "$HERE/list_files.py" "$C" > "$OUT/files.txt"
+echo "== probing $(wc -l <"$OUT/files.txt") files, $JOBS at a time (timeout ${TMO}s, limit $((MEM_KB / 1024)) MiB)"
+export C OUT HERE
+# The shell's "Segmentation fault (core dumped)" notices go to probe.log; the
+# signals themselves are recorded in each side's .rc.
+xargs -a "$OUT/files.txt" -d '\n' -P "$JOBS" -I{} bash -c '
+  f="$1"; d="$OUT/runs/${f//\//__}"
+  case "$f" in cve_hdf5/*) export WITH_H5DUMP=1 ;; esac
+  "$HERE/run_one.sh" "$C/$f" "$d"' _ {} 2>"$OUT/probe.log"
+echo "== comparing"
+"$PY" "$HERE/compare.py" "$OUT" >/dev/null
+t2=$(date +%s)
+cat > "$OUT/meta.json" <<EOF
+{"build_seconds": $((t1 - t0)), "probe_seconds": $((t2 - t1)), "jobs": $JOBS, "timeout_s": $TMO, "mem_kb": $MEM_KB}
+EOF
+export CONFORMANCE_CMD="${CONFORMANCE_CMD:-conformance/run.sh${*:+ $*}}"
+if [ "$REPORT" = 1 ]; then
+  "$PY" "$HERE/report.py" "$OUT" "$REPORT_PATH" "$C"
+  echo "== wrote $REPORT_PATH"
+fi
+if [ "$UPDATE" = 1 ]; then
+  "$PY" "$HERE/check.py" "$OUT" "$HERE/baseline.json" --update
+fi
+"$PY" "$HERE/check.py" "$OUT" "$HERE/baseline.json"

conformance/run_one.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# run_one.sh <file> <outdir>
+#
+# Probe one file with clawhdf5 (PROBE) and with h5py (PY ref.py), and with
+# h5dump too when WITH_H5DUMP is set. Each side runs under a timeout (TMO
+# seconds, SIGKILL) and an address-space limit (MEM_KB), with core dumps off.
+# Writes <outdir>/<side>.{json,err,rc}; rc 137 = killed by the timeout.
+set -u
+f="$1"; out="$2"; mkdir -p "$out"
+HERE="$(cd "$(dirname "$0")" && pwd)"
+: "${PROBE:?PROBE must name the conformance-probe binary}"
+: "${PY:?PY must name a python with h5py}"
+TMO="${TMO:-20}"
+MEM_KB="${MEM_KB:-4194304}"
+run() { # name cmd...
+  local name=$1; shift
+  ( ulimit -v "$MEM_KB"; ulimit -c 0; RUST_BACKTRACE=1 exec timeout -s KILL "$TMO" "$@" ) \
+      >"$out/$name.json" 2>"$out/$name.err"
+  echo $? >"$out/$name.rc"
+}
+run ours "$PROBE" "$f"
+run ref "$PY" "$HERE/ref.py" "$f"
+if [ -n "${WITH_H5DUMP:-}" ]; then
+  run h5dump h5dump "$f"
+  : >"$out/h5dump.json" # h5dump's text dump is not compared, only its exit status
+fi
+exit 0

crates/clawhdf5-accel/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-accel"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "SIMD-accelerated operations for rustyhdf5"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"

crates/clawhdf5-accel/src/avx2.rs

@@ -25,6 +25,55 @@ unsafe fn hsum_256(v: __m256) -> f32 {
     _mm_cvtss_f32(result)
 }
 
+/// AVX2 dot product of two `i8` slices, widened to `i32`.
+///
+/// Each 16-byte half is sign-extended to sixteen `i16` lanes and multiplied
+/// pairwise with `madd_epi16`, which sums adjacent products straight into
+/// eight `i32` lanes — the widening that an autovectorised scalar loop does
+/// in several shuffles is one instruction here. A pair sum is at most
+/// `2 * 127 * 127`, far inside `i32`.
+///
+/// # Safety
+/// Caller must verify is_x86_feature_detected!("avx2").
+// SAFETY: Caller must have verified AVX2 via is_x86_feature_detected!.
+#[target_feature(enable = "avx2")]
+pub unsafe fn dot_i8(a: &[i8], b: &[i8]) -> i32 {
+    // SAFETY: Caller guarantees AVX2 is available per the # Safety contract;
+    // every load reads 32 bytes at an index checked against `len` first.
+    unsafe {
+        assert_eq!(a.len(), b.len());
+        let len = a.len();
+        let mut i = 0;
+        let mut acc0 = _mm256_setzero_si256();
+        let mut acc1 = _mm256_setzero_si256();
+
+        while i + 32 <= len {
+            let va = _mm256_loadu_si256(a.as_ptr().add(i).cast());
+            let vb = _mm256_loadu_si256(b.as_ptr().add(i).cast());
+            let a_lo = _mm256_cvtepi8_epi16(_mm256_castsi256_si128(va));
+            let b_lo = _mm256_cvtepi8_epi16(_mm256_castsi256_si128(vb));
+            let a_hi = _mm256_cvtepi8_epi16(_mm256_extracti128_si256(va, 1));
+            let b_hi = _mm256_cvtepi8_epi16(_mm256_extracti128_si256(vb, 1));
+            acc0 = _mm256_add_epi32(acc0, _mm256_madd_epi16(a_lo, b_lo));
+            acc1 = _mm256_add_epi32(acc1, _mm256_madd_epi16(a_hi, b_hi));
+            i += 32;
+        }
+
+        // Horizontal sum of the eight i32 lanes.
+        let v = _mm256_add_epi32(acc0, acc1);
+        let s128 = _mm_add_epi32(_mm256_castsi256_si128(v), _mm256_extracti128_si256(v, 1));
+        let s64 = _mm_add_epi32(s128, _mm_unpackhi_epi64(s128, s128));
+        let s32 = _mm_add_epi32(s64, _mm_shuffle_epi32(s64, 0b01));
+        let mut sum = _mm_cvtsi128_si32(s32);
+
+        while i < len {
+            sum += i32::from(a[i]) * i32::from(b[i]);
+            i += 1;
+        }
+        sum
+    }
+}
+
 /// AVX2 dot product for f32 slices.
 ///
 /// # Safety

crates/clawhdf5-accel/src/lib.rs

@@ -122,6 +122,36 @@ pub fn dot_product(a: &[f32], b: &[f32]) -> f32 {
     }
 }
 
+/// Dot product of two `i8` slices, widened to `i32`.
+///
+/// The kernel behind int8-quantised vector search. On x86-64 it uses the AVX2
+/// path whenever AVX2 is present (including on AVX-512 machines, where it is
+/// what the f32 kernels use too on a default build). On aarch64 it uses the
+/// ARMv8.2 `SDOT` instruction when the CPU has the dot-product extension, and
+/// plain NEON otherwise.
+pub fn dot_i8(a: &[i8], b: &[i8]) -> i32 {
+    match detect_backend() {
+        #[cfg(target_arch = "aarch64")]
+        Backend::Neon => {
+            if std::arch::is_aarch64_feature_detected!("dotprod") {
+                // SAFETY: the dotprod extension was just detected at runtime.
+                unsafe { neon::dot_i8_dotprod(a, b) }
+            } else {
+                // SAFETY: NEON is always available on aarch64.
+                unsafe { neon::dot_i8(a, b) }
+            }
+        }
+
+        #[cfg(target_arch = "x86_64")]
+        // SAFETY: both variants imply AVX2 was detected at runtime (the
+        // AVX-512 backend is only selected on CPUs that also have AVX2).
+        Backend::Avx2 | Backend::Avx512 if is_x86_feature_detected!("avx2") => unsafe {
+            avx2::dot_i8(a, b)
+        },
+        _ => scalar::dot_i8(a, b),
+    }
+}
+
 /// Compute the L2 norm (magnitude) of a vector.
 pub fn vector_norm(v: &[f32]) -> f32 {
     dot_product(v, v).sqrt()
@@ -713,3 +743,78 @@ mod tests {
         }
     }
 }
+
+#[cfg(test)]
+mod dot_i8_tests {
+    use super::*;
+
+    fn codes(n: usize, seed: u64) -> Vec<i8> {
+        let mut state = seed;
+        (0..n)
+            .map(|_| {
+                state = state
+                    .wrapping_mul(6_364_136_223_846_793_005)
+                    .wrapping_add(1_442_695_040_888_963_407);
+                // Full range, including the extremes.
+                ((state >> 56) as u8) as i8
+            })
+            .collect()
+    }
+
+    #[test]
+    fn dispatched_kernel_matches_scalar_exactly() {
+        // Integer arithmetic: the SIMD path must agree bit for bit, at every
+        // length — including ones that are not multiples of the 32-byte block,
+        // which exercise the tail.
+        for len in [0, 1, 7, 31, 32, 33, 63, 64, 100, 384, 385, 1536] {
+            let a = codes(len, 1 + len as u64);
+            let b = codes(len, 1000 + len as u64);
+            assert_eq!(dot_i8(&a, &b), scalar::dot_i8(&a, &b), "len {len}");
+        }
+    }
+
+    /// Dispatch only ever takes one path on a given CPU, so on a machine with
+    /// the dot-product extension the plain-NEON kernel would otherwise go
+    /// untested. Check each aarch64 kernel against scalar directly.
+    #[cfg(target_arch = "aarch64")]
+    #[test]
+    fn every_aarch64_kernel_matches_scalar_exactly() {
+        for len in [0, 1, 7, 15, 16, 17, 31, 32, 33, 63, 64, 100, 384, 385, 1536] {
+            let a = codes(len, 7 + len as u64);
+            let b = codes(len, 7000 + len as u64);
+            let want = scalar::dot_i8(&a, &b);
+            // SAFETY: NEON is always available on aarch64.
+            assert_eq!(unsafe { neon::dot_i8(&a, &b) }, want, "neon, len {len}");
+            if std::arch::is_aarch64_feature_detected!("dotprod") {
+                // SAFETY: the dotprod extension was just detected.
+                assert_eq!(
+                    unsafe { neon::dot_i8_dotprod(&a, &b) },
+                    want,
+                    "dotprod, len {len}"
+                );
+            }
+        }
+        // The extremes, through both kernels.
+        let lo = vec![-128i8; 4096];
+        let hi = vec![127i8; 4096];
+        // SAFETY: NEON is always available on aarch64.
+        assert_eq!(unsafe { neon::dot_i8(&lo, &lo) }, 4096 * 128 * 128);
+        // SAFETY: NEON is always available on aarch64.
+        assert_eq!(unsafe { neon::dot_i8(&lo, &hi) }, -4096 * 128 * 127);
+        if std::arch::is_aarch64_feature_detected!("dotprod") {
+            // SAFETY: the dotprod extension was just detected.
+            assert_eq!(unsafe { neon::dot_i8_dotprod(&lo, &lo) }, 4096 * 128 * 128);
+            // SAFETY: the dotprod extension was just detected.
+            assert_eq!(unsafe { neon::dot_i8_dotprod(&lo, &hi) }, -4096 * 128 * 127);
+        }
+    }
+
+    #[test]
+    fn extremes_do_not_overflow() {
+        // -128 * -128 is the largest product; a long run of it must still fit.
+        let a = vec![-128i8; 4096];
+        assert_eq!(dot_i8(&a, &a), 4096 * 128 * 128);
+        let b = vec![127i8; 4096];
+        assert_eq!(dot_i8(&a, &b), -4096 * 128 * 127);
+    }
+}

crates/clawhdf5-accel/src/neon.rs

@@ -180,3 +180,130 @@ pub fn checksum_fletcher32(data: &[u8]) -> u32 {
 
     (sum2 << 16) | sum1
 }
+
+/// NEON dot product of two `i8` slices, widened to `i32`, for any aarch64 CPU.
+///
+/// `vmull_s8` multiplies eight lanes into `i16` — even `-128 * -128` is 16 384,
+/// inside `i16` — and `vpadalq_s16` adds adjacent pairs of those into `i32`
+/// accumulators, so nothing can overflow before the final horizontal sum.
+///
+/// CPUs with the ARMv8.2 dot-product extension should use
+/// [`dot_i8_dotprod`], which does the multiply and the accumulate in one
+/// instruction.
+///
+/// # Safety
+/// Caller must ensure aarch64 target (NEON always available).
+// SAFETY: NEON is always available on aarch64 targets; caller guarantees aarch64.
+#[target_feature(enable = "neon")]
+pub unsafe fn dot_i8(a: &[i8], b: &[i8]) -> i32 {
+    assert_eq!(a.len(), b.len());
+    let len = a.len();
+    let mut i = 0;
+    let mut acc0 = vdupq_n_s32(0);
+    let mut acc1 = vdupq_n_s32(0);
+
+    while i + 16 <= len {
+        // SAFETY: NEON is available per the # Safety contract, and both
+        // 16-byte loads start at an index checked against `len` above.
+        unsafe {
+            let va = vld1q_s8(a.as_ptr().add(i));
+            let vb = vld1q_s8(b.as_ptr().add(i));
+            acc0 = vpadalq_s16(acc0, vmull_s8(vget_low_s8(va), vget_low_s8(vb)));
+            acc1 = vpadalq_s16(acc1, vmull_high_s8(va, vb));
+        }
+        i += 16;
+    }
+
+    let mut sum = vaddvq_s32(vaddq_s32(acc0, acc1));
+    while i < len {
+        sum += i32::from(a[i]) * i32::from(b[i]);
+        i += 1;
+    }
+    sum
+}
+
+/// One `SDOT`: for each of the four `i32` lanes of `acc`, add the dot
+/// product of the corresponding four `i8` pairs from `a` and `b`.
+///
+/// Written as inline assembly because the `vdotq_s32` intrinsic is still
+/// behind the unstable `stdarch_neon_dotprod` feature; inline assembly is
+/// stable on aarch64.
+///
+/// # Safety
+/// Caller must ensure the CPU supports the `dotprod` extension.
+#[inline]
+#[target_feature(enable = "neon,dotprod")]
+unsafe fn sdot(acc: int32x4_t, a: int8x16_t, b: int8x16_t) -> int32x4_t {
+    let mut acc = acc;
+    // SAFETY: `dotprod` is enabled for this function and the caller
+    // guarantees the CPU supports it. The instruction reads only its three
+    // vector registers and touches no memory.
+    unsafe {
+        std::arch::asm!(
+            "sdot {acc:v}.4s, {a:v}.16b, {b:v}.16b",
+            acc = inout(vreg) acc,
+            a = in(vreg) a,
+            b = in(vreg) b,
+            options(pure, nomem, nostack),
+        );
+    }
+    acc
+}
+
+/// NEON dot product of two `i8` slices using the ARMv8.2 dot-product
+/// extension (`SDOT`): sixteen multiply-accumulates per instruction, straight
+/// into `i32` lanes.
+///
+/// Present on the cores this crate actually runs on — Cortex-A76 and later
+/// (Raspberry Pi 5, current Android phones), Neoverse-N1 (Graviton2, Ampere
+/// Altra), and every Apple Silicon generation.
+///
+/// # Safety
+/// Caller must verify `is_aarch64_feature_detected!("dotprod")`.
+// SAFETY: caller has verified the dotprod extension at runtime.
+#[target_feature(enable = "neon,dotprod")]
+pub unsafe fn dot_i8_dotprod(a: &[i8], b: &[i8]) -> i32 {
+    assert_eq!(a.len(), b.len());
+    let len = a.len();
+    let mut i = 0;
+    let mut acc0 = vdupq_n_s32(0);
+    let mut acc1 = vdupq_n_s32(0);
+
+    // Two independent accumulators so consecutive SDOTs are not serialised on
+    // one register.
+    while i + 32 <= len {
+        // SAFETY: dotprod is available per the # Safety contract, and every
+        // 16-byte load starts at an index checked against `len` above.
+        unsafe {
+            acc0 = sdot(
+                acc0,
+                vld1q_s8(a.as_ptr().add(i)),
+                vld1q_s8(b.as_ptr().add(i)),
+            );
+            acc1 = sdot(
+                acc1,
+                vld1q_s8(a.as_ptr().add(i + 16)),
+                vld1q_s8(b.as_ptr().add(i + 16)),
+            );
+        }
+        i += 32;
+    }
+    if i + 16 <= len {
+        // SAFETY: as above; the load is bounds-checked by this condition.
+        unsafe {
+            acc0 = sdot(
+                acc0,
+                vld1q_s8(a.as_ptr().add(i)),
+                vld1q_s8(b.as_ptr().add(i)),
+            );
+        }
+        i += 16;
+    }
+
+    let mut sum = vaddvq_s32(vaddq_s32(acc0, acc1));
+    while i < len {
+        sum += i32::from(a[i]) * i32::from(b[i]);
+        i += 1;
+    }
+    sum
+}

crates/clawhdf5-accel/src/scalar.rs

@@ -140,3 +140,33 @@ fn f16_to_f32_soft(h: u16) -> f32 {
 
     f32::from_bits(f32_bits)
 }
+
+/// Dot product of two `i8` slices, widened to `i32`.
+///
+/// `dim` terms of at most `127 * 127` fit an `i32` for any realistic
+/// dimension (over 130 000 terms before overflow is possible).
+pub fn dot_i8(a: &[i8], b: &[i8]) -> i32 {
+    assert_eq!(a.len(), b.len());
+    // Four independent accumulators over 32-lane blocks: the widening product
+    // has to sit in a fixed-length chunk for the vectoriser to see it, and the
+    // separate accumulators keep it off one dependency chain.
+    const LANE: usize = 8;
+    let (a_blocks, a_tail) = a.as_chunks::<{ LANE * 4 }>();
+    let (b_blocks, b_tail) = b.as_chunks::<{ LANE * 4 }>();
+    let mut acc = [0i32; 4];
+    for (x, y) in a_blocks.iter().zip(b_blocks) {
+        for (lane, slot) in acc.iter_mut().enumerate() {
+            let mut sum = 0i32;
+            for k in 0..LANE {
+                sum += i32::from(x[lane * LANE + k]) * i32::from(y[lane * LANE + k]);
+            }
+            *slot += sum;
+        }
+    }
+    let tail: i32 = a_tail
+        .iter()
+        .zip(b_tail)
+        .map(|(&x, &y)| i32::from(x) * i32::from(y))
+        .sum();
+    acc[0] + acc[1] + acc[2] + acc[3] + tail
+}

crates/clawhdf5-agent/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-agent"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "HDF5-backed persistent memory store for on-device AI agents"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
@@ -10,14 +11,18 @@ keywords = ["agent", "memory", "hdf5", "vector-search", "embedding"]
 categories = ["database", "science", "algorithms"]
 
 [dependencies]
-clawhdf5-format = { path = "../clawhdf5-format", version = "2.6.0", features = ["parallel", "fast-checksum"] }
-clawhdf5 = { path = "../clawhdf5", version = "2.6.0" }
-clawhdf5-io = { path = "../clawhdf5-io", version = "2.6.0", features = ["mmap"] }
-clawhdf5-accel = { path = "../clawhdf5-accel", version = "2.6.0" }
-clawhdf5-ann = { path = "../clawhdf5-ann", version = "2.6.0", optional = true }
-clawhdf5-gpu = { path = "../clawhdf5-gpu", version = "2.6.0", optional = true, default-features = false }
+clawhdf5-format = { path = "../clawhdf5-format", version = "2.7.0", features = ["parallel", "fast-checksum"] }
+clawhdf5 = { path = "../clawhdf5", version = "2.7.0" }
+clawhdf5-io = { path = "../clawhdf5-io", version = "2.7.0", features = ["mmap"] }
+clawhdf5-accel = { path = "../clawhdf5-accel", version = "2.7.0" }
+clawhdf5-ann = { path = "../clawhdf5-ann", version = "2.7.0", optional = true }
+clawhdf5-gpu = { path = "../clawhdf5-gpu", version = "2.7.0", optional = true, default-features = false }
 serde = { workspace = true }
 byteorder = "1"
+# Signed checkpoints (MemoryConfig-independent; see `signing`). Pure Rust.
+ed25519-dalek = { version = "2", features = ["rand_core"] }
+sha2 = "0.10"
+rand_core = { version = "0.6", features = ["getrandom"] }
 half = { workspace = true, optional = true }
 rayon = { version = "1", optional = true }
 matrixmultiply = { version = "0.3", optional = true }
@@ -44,6 +49,10 @@ harness = false
 name = "memory_bench"
 harness = false
 
+[[bench]]
+name = "multimodal_bench"
+harness = false
+
 [features]
 default = ["float16", "hnsw", "parallel"]
 float16 = ["half"]
@@ -59,7 +68,6 @@ zstd = ["clawhdf5/zstd"]
 # `--no-default-features` (plus re-enabling other defaults) to force the exact
 # linear cosine scan.
 hnsw = ["clawhdf5-ann"]
-agent = []
 gpu = ["clawhdf5-gpu/gpu-wgpu"]
 fast-math = ["matrixmultiply"]
 accelerate = ["accelerate-src", "cblas-sys"]

crates/clawhdf5-agent/benches/multimodal_bench.rs

@@ -0,0 +1,107 @@
+//! Multi-modal memory search benchmarks (`clawhdf5_agent::multimodal`).
+//!
+//! Covers `MultiModalStore::search_cross_modal` (every embedding of every
+//! record, whatever its modality) and, for comparison,
+//! `MultiModalStore::search_by_modality` restricted to one modality.
+//!
+//! Corpus: N records (1K and 10K), each carrying two 384-dim embeddings —
+//! a text embedding of its caption plus one embedding of its primary modality,
+//! cycling Image / Audio / Video — so a cross-modal query scores 2N vectors.
+//! All data comes from a fixed-seed LCG, so every run sees the same corpus.
+//!
+//! Run: `cargo bench -p clawhdf5-agent --bench multimodal_bench`
+
+use std::collections::HashMap;
+
+use clawhdf5_agent::multimodal::{
+    MediaRef, ModalEmbedding, Modality, MultiModalRecord, MultiModalStore,
+};
+use criterion::{BenchmarkId, Criterion, criterion_group, criterion_main};
+
+// ---------------------------------------------------------------------------
+// Simple deterministic PRNG (LCG), same as the other agent benches
+// ---------------------------------------------------------------------------
+
+struct Rng(u32);
+
+impl Rng {
+    fn new(seed: u32) -> Self {
+        Self(seed)
+    }
+    fn next_u32(&mut self) -> u32 {
+        self.0 = self.0.wrapping_mul(1103515245).wrapping_add(12345);
+        self.0 >> 16
+    }
+    fn next_f32(&mut self) -> f32 {
+        self.next_u32() as f32 / 65536.0 - 0.5
+    }
+}
+
+fn make_vec(rng: &mut Rng, dim: usize) -> Vec<f32> {
+    (0..dim).map(|_| rng.next_f32()).collect()
+}
+
+// ---------------------------------------------------------------------------
+// Corpus
+// ---------------------------------------------------------------------------
+
+const DIM: usize = 384;
+const K: usize = 10;
+
+const MEDIA: [(Modality, &str, &str); 3] = [
+    (Modality::Image, "image/png", "clip-vit-base"),
+    (Modality::Audio, "audio/wav", "clap-base"),
+    (Modality::Video, "video/mp4", "xclip-base"),
+];
+
+fn build_store(n: usize, seed: u32) -> MultiModalStore {
+    let mut rng = Rng::new(seed);
+    let mut store = MultiModalStore::new();
+    for i in 0..n {
+        let (modality, mime, model) = &MEDIA[i % MEDIA.len()];
+        let embeddings = vec![
+            ModalEmbedding::new(Modality::Text, make_vec(&mut rng, DIM), "minilm-l6"),
+            ModalEmbedding::new(modality.clone(), make_vec(&mut rng, DIM), *model),
+        ];
+        store.add_record(MultiModalRecord {
+            id: 0,
+            primary_modality: modality.clone(),
+            text_content: Some(format!("{modality} memory {i}")),
+            media_ref: Some(MediaRef::path(format!("/media/{i}"), *mime)),
+            embeddings,
+            observation: None,
+            timestamp: 1_700_000_000.0 + i as f64,
+            metadata: HashMap::new(),
+        });
+    }
+    store
+}
+
+// ---------------------------------------------------------------------------
+// Benchmarks
+// ---------------------------------------------------------------------------
+
+fn multimodal_search_benches(c: &mut Criterion) {
+    let query = make_vec(&mut Rng::new(99), DIM);
+
+    let mut group = c.benchmark_group("multimodal_search");
+    group.sample_size(50);
+
+    for (label, n) in [("1k", 1_000usize), ("10k", 10_000)] {
+        let store = build_store(n, 42);
+        assert_eq!(store.count(), n);
+
+        group.bench_with_input(BenchmarkId::new("cross_modal", label), &n, |b, _| {
+            b.iter(|| store.search_cross_modal(&query, K));
+        });
+
+        group.bench_with_input(BenchmarkId::new("by_modality_image", label), &n, |b, _| {
+            b.iter(|| store.search_by_modality(&Modality::Image, &query, K));
+        });
+    }
+
+    group.finish();
+}
+
+criterion_group!(multimodal_benches, multimodal_search_benches);
+criterion_main!(multimodal_benches);

crates/clawhdf5-agent/src/agents_md.rs

@@ -119,6 +119,9 @@ mod tests {
             wal_enabled: false,
             wal_max_entries: 500,
             quantized_index: false,
+            hnsw_m: 16,
+            hnsw_ef_construction: 64,
+            hnsw_ef_search: 0,
         }
     }
 

crates/clawhdf5-agent/src/bm25.rs

@@ -88,8 +88,11 @@ impl BM25Index {
     /// Search the index for a query, returning the top `k` results
     /// as `(doc_id, score)` pairs sorted by score descending.
     ///
-    /// Uses Block-Max WAND for early termination when remaining documents
-    /// cannot beat the current top-k threshold.
+    /// Scores every matching document exhaustively, then keeps the top `k`.
+    /// There is no early termination (WAND, MaxScore): the store's hot path
+    /// is [`scores`](Self::scores), because score fusion normalises over the
+    /// whole matching set and so needs every score, which no pruning scheme
+    /// can skip. This method is for BM25-only callers.
     pub fn search(&self, query: &str, k: usize) -> Vec<(usize, f32)> {
         if k == 0 {
             return Vec::new();
@@ -561,8 +564,9 @@ mod tests {
     }
 
     #[test]
-    fn wand_returns_same_results_as_exhaustive() {
-        // WAND-style search should produce same scores as exhaustive
+    fn top_k_search_matches_ranking_every_score() {
+        // `search` must agree with ranking the full `scores` set — the
+        // bounded heap is an optimisation over sorting, not an approximation.
         let docs: Vec<String> = (0..100)
             .map(|i| {
                 if i % 3 == 0 {

crates/clawhdf5-agent/src/cache.rs

@@ -1,6 +1,7 @@
 //! In-memory cache for memory entries, sessions, and knowledge graph.
 
 use crate::vector_search;
+use clawhdf5_format::float16::round_to_f16;
 
 /// Every entry's embedding, in one contiguous `[N x dim]` buffer.
 ///
@@ -149,6 +150,11 @@ pub struct MemoryCache {
     pub norms: Vec<f32>,
     /// Hebbian activation weights (default 1.0 per entry).
     pub activation_weights: Vec<f32>,
+    /// Round every embedding to IEEE half precision as it enters the cache,
+    /// so the cache holds exactly what a `float16` store writes to disk. Set
+    /// it with [`MemoryCache::set_half_precision`], which also rounds the
+    /// rows already held.
+    pub half_precision: bool,
 }
 
 impl MemoryCache {
@@ -164,9 +170,44 @@ impl MemoryCache {
             embedding_dim,
             norms: Vec::new(),
             activation_weights: Vec::new(),
+            half_precision: false,
         }
     }
 
+    /// Switch half-precision rounding on or off. Turning it on rounds every
+    /// embedding already held (and recomputes norms where one changed) —
+    /// e.g. a `float16` store whose last checkpoint predates half-precision
+    /// storage and so is still `f32` on disk.
+    pub fn set_half_precision(&mut self, on: bool) {
+        self.half_precision = on;
+        if !on {
+            return;
+        }
+        for i in 0..self.embeddings.len() {
+            let row = &self.embeddings[i];
+            if row
+                .iter()
+                .all(|&v| round_to_f16(v).to_bits() == v.to_bits())
+            {
+                continue;
+            }
+            let rounded: Vec<f32> = row.iter().map(|&v| round_to_f16(v)).collect();
+            self.norms[i] = vector_search::compute_norm(&rounded);
+            self.embeddings.set(i, &rounded);
+        }
+    }
+
+    /// The embedding as the cache will hold it: rounded to half precision
+    /// when [`Self::half_precision`] is on, otherwise unchanged.
+    fn stored_form(&self, mut embedding: Vec<f32>) -> Vec<f32> {
+        if self.half_precision {
+            for v in &mut embedding {
+                *v = round_to_f16(*v);
+            }
+        }
+        embedding
+    }
+
     /// Kept for callers that used to have to re-flatten after a bulk load.
     /// The buffer is always flat now, so there is nothing to rebuild.
     #[deprecated(note = "embeddings are stored flat; this is a no-op")]
@@ -202,6 +243,7 @@ impl MemoryCache {
         tags: String,
     ) -> usize {
         let idx = self.chunks.len();
+        let embedding = self.stored_form(embedding);
         let norm = vector_search::compute_norm(&embedding);
         self.chunks.push(chunk);
         self.embeddings.push(&embedding);
@@ -240,6 +282,7 @@ impl MemoryCache {
         session_id: String,
     ) {
         if idx < self.chunks.len() {
+            let embedding = self.stored_form(embedding);
             let norm = vector_search::compute_norm(&embedding);
             self.chunks[idx] = chunk;
             self.embeddings.set(idx, &embedding);
@@ -439,4 +482,60 @@ mod tests {
             .reset_from(2, vec![vec![1.0, 2.0], vec![3.0, 4.0]]);
         assert_eq!(cache.embeddings.as_flat(), vec![1.0, 2.0, 3.0, 4.0]);
     }
+
+    #[test]
+    fn set_half_precision_rounds_existing_rows_and_their_norms() {
+        // A store with float16 set whose checkpoint is still f32 on disk
+        // loads full-precision rows; switching rounding on must bring them to
+        // exactly what the next checkpoint will write.
+        let mut cache = MemoryCache::new(3);
+        cache.push(
+            "a".into(),
+            vec![0.1, 0.2, 0.3],
+            "c".into(),
+            0.0,
+            "s".into(),
+            "".into(),
+        );
+        cache.push(
+            "b".into(),
+            vec![0.5, 0.25, 1.0],
+            "c".into(),
+            0.0,
+            "s".into(),
+            "".into(),
+        );
+        let exact_norm = cache.norms[0];
+
+        cache.set_half_precision(true);
+        let row0: Vec<f32> = [0.1f32, 0.2, 0.3]
+            .iter()
+            .map(|&v| round_to_f16(v))
+            .collect();
+        assert_eq!(&cache.embeddings[0], row0.as_slice());
+        assert_eq!(cache.norms[0], vector_search::compute_norm(&row0));
+        assert_ne!(cache.norms[0], exact_norm);
+        // Already representable: untouched.
+        assert_eq!(&cache.embeddings[1], &[0.5, 0.25, 1.0]);
+
+        // New rows are rounded as they arrive, and updates too.
+        cache.push(
+            "c".into(),
+            vec![0.1, 0.0, 0.0],
+            "c".into(),
+            0.0,
+            "s".into(),
+            "".into(),
+        );
+        assert_eq!(cache.embeddings[2][0], round_to_f16(0.1));
+        cache.update(
+            2,
+            "c".into(),
+            vec![0.3, 0.0, 0.0],
+            "c".into(),
+            0.0,
+            "s".into(),
+        );
+        assert_eq!(cache.embeddings[2][0], round_to_f16(0.3));
+    }
 }

crates/clawhdf5-agent/src/consolidation.rs

@@ -144,9 +144,44 @@ pub struct ConsolidationStats {
 
 pub struct ImportanceScorer;
 
+/// Sum of squares, in 8-wide lanes so it vectorises.
+fn sum_of_squares(a: &[f32]) -> f32 {
+    let (blocks, tail) = a.as_chunks::<8>();
+    let mut acc = [0.0f32; 8];
+    for b in blocks {
+        for i in 0..8 {
+            acc[i] += b[i] * b[i];
+        }
+    }
+    acc.iter().sum::<f32>() + tail.iter().map(|x| x * x).sum::<f32>()
+}
+
+/// `(a · b, |b|²)` in one pass over equal-length slices, in 8-wide lanes.
+fn dot_and_norm2(a: &[f32], b: &[f32]) -> (f32, f32) {
+    let (a_blocks, a_tail) = a.as_chunks::<8>();
+    let (b_blocks, b_tail) = b.as_chunks::<8>();
+    let mut dot = [0.0f32; 8];
+    let mut nb = [0.0f32; 8];
+    for (x, y) in a_blocks.iter().zip(b_blocks) {
+        for i in 0..8 {
+            dot[i] += x[i] * y[i];
+            nb[i] += y[i] * y[i];
+        }
+    }
+    let mut d = dot.iter().sum::<f32>();
+    let mut n = nb.iter().sum::<f32>();
+    for (x, y) in a_tail.iter().zip(b_tail) {
+        d += x * y;
+        n += y * y;
+    }
+    (d, n)
+}
+
 impl ImportanceScorer {
     /// Cosine similarity between two embedding slices.
-    /// Returns 0.0 if either norm is zero.
+    /// Returns 0.0 if either norm is zero. The reference that
+    /// [`Self::score_surprise`] is tested against.
+    #[cfg(test)]
     fn cosine_similarity(a: &[f32], b: &[f32]) -> f32 {
         let len = a.len().min(b.len());
         if len == 0 {
@@ -167,13 +202,54 @@ impl ImportanceScorer {
 
     /// Novelty score: 1.0 − max cosine similarity against all existing records.
     /// Returns 1.0 when there are no existing memories.
+    ///
+    /// Same result as the reference cosine similarity against each record, but the
+    /// new embedding's norm is computed once rather than per record, each
+    /// record costs one fused pass (dot product and its norm together) rather
+    /// than three, and a large working set is scored in parallel. Every insert
+    /// scores against the whole working tier, so this is what an unbounded
+    /// working tier pays for: at 100K records it was the difference between a
+    /// benchmark finishing and not (`BENCHMARKS.md`, "Consolidation Efficiency").
     pub fn score_surprise(embedding: &[f32], existing_memories: &[&MemoryRecord]) -> f32 {
         if existing_memories.is_empty() {
             return 1.0;
         }
+        let query_norm2 = sum_of_squares(embedding);
+        let similarity = |r: &&MemoryRecord| -> f32 {
+            let other = &r.embedding;
+            let len = embedding.len().min(other.len());
+            if len == 0 {
+                return 0.0;
+            }
+            let (dot, other_norm2) = dot_and_norm2(&embedding[..len], &other[..len]);
+            // A shorter record compares against the query's matching prefix.
+            let q2 = if len == embedding.len() {
+                query_norm2
+            } else {
+                sum_of_squares(&embedding[..len])
+            };
+            if q2 == 0.0 || other_norm2 == 0.0 {
+                return 0.0;
+            }
+            dot / (q2.sqrt() * other_norm2.sqrt())
+        };
+        #[cfg(feature = "parallel")]
+        let max_sim = if existing_memories.len() >= 4096 {
+            use rayon::prelude::*;
+            existing_memories
+                .par_iter()
+                .map(similarity)
+                .reduce(|| f32::NEG_INFINITY, f32::max)
+        } else {
+            existing_memories
+                .iter()
+                .map(similarity)
+                .fold(f32::NEG_INFINITY, f32::max)
+        };
+        #[cfg(not(feature = "parallel"))]
         let max_sim = existing_memories
             .iter()
-            .map(|r| Self::cosine_similarity(embedding, &r.embedding))
+            .map(similarity)
             .fold(f32::NEG_INFINITY, f32::max);
         (1.0 - max_sim).clamp(0.0, 1.0)
     }
@@ -471,6 +547,54 @@ impl ConsolidationEngine {
 mod tests {
     use super::*;
 
+    #[test]
+    fn score_surprise_matches_the_reference_cosine() {
+        let mut x = 0x2545_F491_4F6C_DD1Du64;
+        let mut next = || {
+            x ^= x << 13;
+            x ^= x >> 7;
+            x ^= x << 17;
+            (x >> 40) as f32 / (1u64 << 24) as f32 - 0.5
+        };
+        let make = |id: u64, v: Vec<f32>| MemoryRecord {
+            id,
+            chunk: String::new(),
+            embedding: v,
+            tier: MemoryTier::Working,
+            importance: 0.0,
+            access_count: 0,
+            last_accessed: 0.0,
+            created_at: 0.0,
+            source: MemorySource::User,
+        };
+        // Ordinary rows, a shorter one, an empty one and a zero vector; and
+        // enough rows to take the parallel path too.
+        for n in [5usize, 5000] {
+            let mut recs: Vec<MemoryRecord> = (0..n as u64)
+                .map(|i| make(i, (0..37).map(|_| next()).collect()))
+                .collect();
+            recs.push(make(9_000, (0..20).map(|_| next()).collect()));
+            recs.push(make(9_001, Vec::new()));
+            recs.push(make(9_002, vec![0.0; 37]));
+            let refs: Vec<&MemoryRecord> = recs.iter().collect();
+            for _ in 0..5 {
+                let q: Vec<f32> = (0..37).map(|_| next()).collect();
+                let expected = (1.0
+                    - refs
+                        .iter()
+                        .map(|r| ImportanceScorer::cosine_similarity(&q, &r.embedding))
+                        .fold(f32::NEG_INFINITY, f32::max))
+                .clamp(0.0, 1.0);
+                let got = ImportanceScorer::score_surprise(&q, &refs);
+                assert!((got - expected).abs() < 1e-5, "n={n}: {got} vs {expected}");
+            }
+        }
+        assert_eq!(
+            ImportanceScorer::score_surprise(&[0.0; 4], &[&make(1, vec![1.0; 4])]),
+            1.0
+        );
+    }
+
     // Helper: build a simple normalised embedding of given dimension.
     fn unit_vec(dim: usize, hot: usize) -> Vec<f32> {
         let mut v = vec![0.0f32; dim];

crates/clawhdf5-agent/src/hybrid.rs

@@ -65,31 +65,34 @@ pub fn hybrid_search_fused(
 ) -> Vec<(usize, f32)> {
     // Get raw scores from both systems. Request all results so normalization
     // covers the full distribution.
-    // Use parallel search when rayon feature is enabled and vector count > 10K.
-    let vec_scores = {
-        #[cfg(feature = "parallel")]
-        {
-            if vectors.count() > 10_000 {
-                vector_search::parallel_cosine_batch(
-                    query_embedding,
-                    vectors,
-                    tombstones,
-                    vectors.count(),
-                )
-            } else {
-                vector_search::cosine_similarity_batch(query_embedding, vectors, tombstones)
-            }
-        }
-        #[cfg(not(feature = "parallel"))]
-        {
-            vector_search::cosine_similarity_batch(query_embedding, vectors, tombstones)
-        }
-    };
+    let vec_scores = exact_vector_scores(query_embedding, vectors, tombstones);
     let kw_scores = bm25_index.scores(query_text);
 
     fuse(vec_scores, kw_scores, fusion, k)
 }
 
+/// Cosine similarity of `query_embedding` to every vector whose `skip` byte is
+/// 0 (a tombstone, or any other exclusion mask). Parallel above 10K vectors
+/// when the `parallel` feature is on.
+pub fn exact_vector_scores(
+    query_embedding: &[f32],
+    vectors: &(impl crate::vector_search::VectorSet + Sync + ?Sized),
+    skip: &[u8],
+) -> Vec<(usize, f32)> {
+    #[cfg(feature = "parallel")]
+    {
+        if vectors.count() > 10_000 {
+            return vector_search::parallel_cosine_batch(
+                query_embedding,
+                vectors,
+                skip,
+                vectors.count(),
+            );
+        }
+    }
+    vector_search::cosine_similarity_batch(query_embedding, vectors, skip)
+}
+
 /// Merge pre-computed vector-similarity and keyword scores into a single ranking.
 ///
 /// Both score sets are independently min-max normalized to [0, 1] and combined

crates/clawhdf5-agent/src/knowledge.rs

@@ -163,12 +163,13 @@ fn levenshtein(a: &str, b: &str) -> usize {
 /// entities-slice-index map, and an entity-id -> relation-indices map (edges
 /// touching that entity as either source or target).
 ///
-/// Built fresh per traversal call rather than cached on `KnowledgeCache`:
-/// entities/relations are plain `pub` `Vec`s that get pushed to directly
-/// (e.g. `schema.rs`'s load path bypasses `add_entity`/`add_relation`), so a
-/// persistent index would need extra bookkeeping to avoid drifting stale. A
-/// one-off O(V+E) build per call is still a large win over the O(V·E) (BFS)
-/// / O(steps·active·E) (spreading activation) scans it replaces.
+/// Cached on `KnowledgeCache` and checked against a fingerprint of the graph
+/// on every use ([`graph_fingerprint`]). entities/relations are plain `pub`
+/// `Vec`s that get changed directly (e.g. `schema.rs`'s load path bypasses
+/// `add_entity`/`add_relation`), so the cache cannot rely on being told about
+/// changes; the fingerprint notices any of them. Rebuilding it on every
+/// traversal instead made a 2-hop BFS over 1K entities 6.5x slower than the
+/// scan it replaced (24 -> 155 µs; `BENCHMARKS.md`, "Knowledge Graph").
 struct AdjacencyIndex {
     entity_index: HashMap<u64, usize>,
     by_entity: HashMap<u64, Vec<usize>>,
@@ -204,6 +205,45 @@ impl AdjacencyIndex {
     }
 }
 
+/// A hash of everything [`AdjacencyIndex`] depends on — each entity's id and
+/// position, each relation's endpoints and position. One linear pass, no
+/// allocation: far cheaper than building the index, which hashes the same
+/// values into two maps.
+fn graph_fingerprint(entities: &[Entity], relations: &[Relation]) -> u64 {
+    // splitmix64-style mixing; order matters, so positions are covered.
+    fn mix(h: u64, v: u64) -> u64 {
+        let mut z = (h ^ v).wrapping_add(0x9E37_79B9_7F4A_7C15);
+        z = (z ^ (z >> 30)).wrapping_mul(0xBF58_476D_1CE4_E5B9);
+        z = (z ^ (z >> 27)).wrapping_mul(0x94D0_49BB_1331_11EB);
+        z ^ (z >> 31)
+    }
+    let mut h = mix(entities.len() as u64, relations.len() as u64);
+    for e in entities {
+        h = mix(h, e.id);
+    }
+    for r in relations {
+        h = mix(mix(h, r.src), r.tgt);
+    }
+    h
+}
+
+/// The cached [`AdjacencyIndex`] and the fingerprint it was built for.
+/// Cloning a `KnowledgeCache` starts the clone with an empty cache.
+#[derive(Default)]
+struct AdjacencyCache(std::sync::Mutex<Option<(u64, std::sync::Arc<AdjacencyIndex>)>>);
+
+impl Clone for AdjacencyCache {
+    fn clone(&self) -> Self {
+        Self::default()
+    }
+}
+
+impl std::fmt::Debug for AdjacencyCache {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("AdjacencyCache")
+    }
+}
+
 // ---------------------------------------------------------------------------
 // KnowledgeCache
 // ---------------------------------------------------------------------------
@@ -216,6 +256,7 @@ pub struct KnowledgeCache {
     pub alias_strings: Vec<String>,
     pub alias_entity_ids: Vec<i64>,
     next_entity_id: u64,
+    adjacency: AdjacencyCache,
 }
 
 impl KnowledgeCache {
@@ -226,6 +267,7 @@ impl KnowledgeCache {
             alias_strings: Vec::new(),
             alias_entity_ids: Vec::new(),
             next_entity_id: 0,
+            adjacency: AdjacencyCache::default(),
         }
     }
 
@@ -236,9 +278,29 @@ impl KnowledgeCache {
             alias_strings: Vec::new(),
             alias_entity_ids: Vec::new(),
             next_entity_id: next_id,
+            adjacency: AdjacencyCache::default(),
         }
     }
 
+    /// The adjacency index for the graph as it is now: the cached one if the
+    /// graph's fingerprint still matches, otherwise rebuilt and cached.
+    fn adjacency_index(&self) -> std::sync::Arc<AdjacencyIndex> {
+        let fp = graph_fingerprint(&self.entities, &self.relations);
+        let mut slot = self
+            .adjacency
+            .0
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner);
+        if let Some((cached_fp, idx)) = slot.as_ref()
+            && *cached_fp == fp
+        {
+            return idx.clone();
+        }
+        let idx = std::sync::Arc::new(AdjacencyIndex::build(&self.entities, &self.relations));
+        *slot = Some((fp, idx.clone()));
+        idx
+    }
+
     // -----------------------------------------------------------------------
     // Entity management
     // -----------------------------------------------------------------------
@@ -397,7 +459,7 @@ impl KnowledgeCache {
     /// together with their discovered depth.  The seed entity itself is NOT
     /// included.  Traversal follows both outgoing and incoming relation edges.
     pub fn bfs_neighbors(&self, entity_id: u64, max_depth: usize) -> Vec<(Entity, usize)> {
-        let idx = AdjacencyIndex::build(&self.entities, &self.relations);
+        let idx = self.adjacency_index();
         let mut visited: HashSet<u64> = HashSet::new();
         let mut queue: VecDeque<(u64, usize)> = VecDeque::new();
         let mut results: Vec<(Entity, usize)> = Vec::new();
@@ -502,7 +564,7 @@ impl KnowledgeCache {
         min_activation: f32,
         max_steps: usize,
     ) -> Vec<(u64, f32)> {
-        let idx = AdjacencyIndex::build(&self.entities, &self.relations);
+        let idx = self.adjacency_index();
         let mut activation: HashMap<u64, f32> = HashMap::new();
 
         // Initialise seeds with activation 1.0.
@@ -631,6 +693,51 @@ impl Default for KnowledgeCache {
 mod tests {
     use super::*;
 
+    #[test]
+    fn cached_adjacency_sees_direct_changes_to_the_graph() {
+        // The index is cached across traversals, but entities/relations are
+        // pub Vecs anyone can edit; every kind of edit must be seen.
+        let mut kg = KnowledgeCache::new();
+        let a = kg.add_entity("a", "t", -1);
+        let b = kg.add_entity("b", "t", -1);
+        let c = kg.add_entity("c", "t", -1);
+        kg.add_relation(a, b, "r", 1.0);
+        let ids = |kg: &KnowledgeCache| -> Vec<u64> {
+            let mut v: Vec<u64> = kg.bfs_neighbors(a, 3).iter().map(|(e, _)| e.id).collect();
+            v.sort();
+            v
+        };
+        assert_eq!(ids(&kg), vec![b]);
+        assert_eq!(ids(&kg), vec![b], "cached index reused");
+
+        // Pushed directly, bypassing add_relation.
+        kg.relations.push(Relation {
+            src: b,
+            tgt: c,
+            ..Relation::default()
+        });
+        assert_eq!(ids(&kg), vec![b, c]);
+
+        // Rewired in place: same lengths, different edge.
+        kg.relations[1].tgt = a;
+        assert_eq!(ids(&kg), vec![b]);
+
+        // Removed and replaced: same lengths again.
+        kg.relations.pop();
+        kg.relations.push(Relation {
+            src: a,
+            tgt: c,
+            ..Relation::default()
+        });
+        assert_eq!(ids(&kg), vec![b, c]);
+        let act: Vec<u64> = kg
+            .spreading_activation(&[a], 0.5, 0.0, 2)
+            .iter()
+            .map(|(id, _)| *id)
+            .collect();
+        assert!(act.contains(&c));
+    }
+
     // -----------------------------------------------------------------------
     // Original tests — must remain passing
     // -----------------------------------------------------------------------

crates/clawhdf5-agent/src/lib.rs

@@ -1,4 +1,4 @@
-//! ZeroClaw agent memory HDF5 backend.
+//! Agent memory stored in a single HDF5 file.
 //!
 //! Provides persistent memory storage for AI agents using HDF5 files.
 //! All data is cached in-memory for fast access and flushed to disk
@@ -36,6 +36,7 @@ pub mod reranker;
 pub mod schema;
 pub mod search;
 pub mod session;
+pub mod signing;
 pub mod storage;
 mod store_lock;
 pub mod temporal;
@@ -63,25 +64,22 @@ use std::path::{Path, PathBuf};
 use cache::MemoryCache;
 #[cfg(feature = "hnsw")]
 use clawhdf5_ann::{DistanceMetric, HnswIndex, Storage};
+use clawhdf5_format::float16::round_to_f16;
 use ephemeral::{EphemeralConfig, EphemeralStore};
 
-/// HNSW construction parameters used for the agent's vector index. Cosine is the
-/// agent's similarity metric, so the index is built with cosine distance.
-#[cfg(feature = "hnsw")]
-const HNSW_M: usize = 16;
-#[cfg(feature = "hnsw")]
-const HNSW_EF_CONSTRUCTION: usize = 64;
 // EphemeralEntry and EphemeralStats are part of the crate public API via
 // the `ephemeral` module; they are not needed directly in lib.rs internals.
 #[allow(unused_imports)]
 pub use ephemeral::{EphemeralEntry, EphemeralStats};
 use knowledge::KnowledgeCache;
 use memory_strategy::{Exchange, MemoryStrategy, StrategyOutput};
-use session::SessionCache;
+pub use search::SearchOptions;
+pub use session::{SessionCache, SessionEntry};
 
 // --- Error type ---
 
 #[derive(Debug)]
+#[non_exhaustive]
 pub enum MemoryError {
     Io(std::io::Error),
     Hdf5(String),
@@ -89,6 +87,14 @@ pub enum MemoryError {
     NotFound(String),
     /// Another `HDF5Memory` (in this or another process) has the store open.
     Locked(String),
+    /// A record the store cannot hold as given, e.g. an embedding value
+    /// outside the half-precision range of a `float16` store.
+    InvalidEntry(String),
+    /// The store's checkpoints are signed and no signing key is set, so a
+    /// checkpoint would leave it unsigned. Set the key with
+    /// [`HDF5Memory::set_signing_key`], or drop the signature on purpose with
+    /// [`HDF5Memory::remove_signature`].
+    SigningKeyRequired(String),
 }
 
 impl std::fmt::Display for MemoryError {
@@ -99,6 +105,8 @@ impl std::fmt::Display for MemoryError {
             MemoryError::Schema(e) => write!(f, "schema error: {e}"),
             MemoryError::NotFound(e) => write!(f, "not found: {e}"),
             MemoryError::Locked(e) => write!(f, "store is locked: {e}"),
+            MemoryError::InvalidEntry(e) => write!(f, "invalid entry: {e}"),
+            MemoryError::SigningKeyRequired(e) => write!(f, "signing key required: {e}"),
         }
     }
 }
@@ -130,6 +138,19 @@ pub struct MemoryConfig {
     pub embedding_dim: usize,
     pub chunk_size: usize,
     pub overlap: usize,
+    /// Store embeddings as IEEE half precision (numpy `float16`): half the
+    /// bytes of the embeddings dataset on disk. Every embedding is rounded to
+    /// the nearest half as it enters the store, in memory as well as on disk,
+    /// so search results are the same before and after a reopen. Values must
+    /// lie within ±65504; a save outside that is `MemoryError::InvalidEntry`.
+    /// Fixed when the store is created (persisted in `/meta`).
+    ///
+    /// **On by default for new stores**: on the full LongMemEval haystack with
+    /// real MiniLM embeddings every retrieval metric matched `f32`, and at
+    /// 100K records the file is 48% smaller (`BENCHMARKS.md`). Existing
+    /// stores keep the setting they were created with. Set it to `false` for
+    /// full-precision embeddings, e.g. for unnormalised vectors that may
+    /// exceed the half-precision range.
     pub float16: bool,
     pub compression: bool,
     pub compression_level: u32,
@@ -140,16 +161,39 @@ pub struct MemoryConfig {
     pub wal_enabled: bool,
     pub wal_max_entries: usize,
     /// Store the vector index's own copy of the embeddings as int8 rather than
-    /// f32, a quarter of the memory.
+    /// f32, a quarter of the memory. **On by default** for new stores.
     ///
     /// The index's copy is the single largest part of a loaded store's
     /// footprint. Quantised distances are approximate, so the candidate pool
     /// is re-scored against the cache's exact embeddings before fusion, which
-    /// restores recall; what it costs is throughput — roughly 13% of queries
-    /// per second and 16% of build time at 100K x 384. See `BENCHMARKS.md`.
+    /// holds recall at the f32 index's level. It is also faster, not slower:
+    /// at equal recall, 1.63x the queries per second on x86-64 (AVX2) and
+    /// 1.18x on a Raspberry Pi 5 (NEON `SDOT`), with builds 1.8x and 2.3x
+    /// faster. See `BENCHMARKS.md`.
+    ///
+    /// Persisted with the store. Stores written before this setting existed
+    /// have no stored value and open as `false`, so reopening an old store
+    /// never changes how its index is held.
     ///
     /// Has no effect without the `hnsw` feature.
     pub quantized_index: bool,
+    /// HNSW graph degree. Higher means a denser graph: better recall, more
+    /// memory and slower builds. Clamped to at least 2 when the index is
+    /// built, since a graph with fewer connections is not one.
+    ///
+    /// Has no effect without the `hnsw` feature.
+    pub hnsw_m: usize,
+    /// Candidate list size while building the HNSW graph. Higher means a
+    /// better graph and a slower build; it does not affect query cost.
+    ///
+    /// Has no effect without the `hnsw` feature.
+    pub hnsw_ef_construction: usize,
+    /// Candidate list size for a query, trading throughput for recall. `0`
+    /// keeps the default, which scales with the requested `k`
+    /// (`max(k * 8, 64)`) so that fusion still sees a useful pool.
+    ///
+    /// Has no effect without the `hnsw` feature.
+    pub hnsw_ef_search: usize,
 }
 
 impl MemoryConfig {
@@ -162,7 +206,7 @@ impl MemoryConfig {
             embedding_dim,
             chunk_size: 512,
             overlap: 50,
-            float16: false,
+            float16: true,
             compression: false,
             compression_level: 0,
             compact_threshold: 0.3,
@@ -171,7 +215,10 @@ impl MemoryConfig {
             created_at,
             wal_enabled: true,
             wal_max_entries: 500,
-            quantized_index: false,
+            quantized_index: true,
+            hnsw_m: 16,
+            hnsw_ef_construction: 64,
+            hnsw_ef_search: 0,
         }
     }
 }
@@ -278,6 +325,12 @@ pub struct HDF5Memory {
     activations_dirty: bool,
     /// Opened with [`HDF5Memory::open_read_only`]: nothing may reach the disk.
     read_only: bool,
+    /// Key that signs every checkpoint; never persisted. See
+    /// [`HDF5Memory::set_signing_key`].
+    signing_key: Option<signing::SigningKey>,
+    /// Checkpoints of this store are signed: the file on disk is, or a key
+    /// has been set. A checkpoint without a key is then refused.
+    signed: bool,
     /// A WAL that `open()` could not read and moved aside; see
     /// [`HDF5Memory::quarantined_wal`].
     quarantined_wal: Option<PathBuf>,
@@ -297,7 +350,8 @@ impl HDF5Memory {
     /// Create a new HDF5 memory file with the given configuration.
     pub fn create(config: MemoryConfig) -> Result<Self> {
         let lock = store_lock::StoreLock::acquire(&config.path)?;
-        let cache = MemoryCache::new(config.embedding_dim);
+        let mut cache = MemoryCache::new(config.embedding_dim);
+        cache.set_half_precision(config.float16);
         let sessions = SessionCache::new();
         let knowledge = KnowledgeCache::new();
 
@@ -332,6 +386,8 @@ impl HDF5Memory {
             bm25_filter: bm25::TokenFilter::default(),
             activations_dirty: false,
             read_only: false,
+            signing_key: None,
+            signed: false,
             quarantined_wal: None,
             _lock: Some(lock),
         })
@@ -510,6 +566,8 @@ impl HDF5Memory {
             bm25_filter: bm25::TokenFilter::default(),
             activations_dirty: false,
             read_only,
+            signing_key: None,
+            signed: checkpoint.signed,
             quarantined_wal,
             _lock: lock,
         })
@@ -670,6 +728,39 @@ impl HDF5Memory {
         }
     }
 
+    /// Sign every checkpoint from now on with `key` (Ed25519). The key is
+    /// never written anywhere; set it again after every `open`. Once a store
+    /// is signed, a checkpoint without the key is refused
+    /// ([`MemoryError::SigningKeyRequired`]) rather than silently leaving it
+    /// unsigned. Setting a different key re-signs the store under that key
+    /// from the next checkpoint; a verifier trusting the old key will then
+    /// reject it, which is the point. Call [`AgentMemory::flush_wal`] to sign
+    /// right away.
+    pub fn set_signing_key(&mut self, key: signing::SigningKey) {
+        self.signing_key = Some(key);
+        self.signed = true;
+    }
+
+    /// Stop signing: the next checkpoint writes the store unsigned. The
+    /// deliberate way out of [`MemoryError::SigningKeyRequired`].
+    pub fn remove_signature(&mut self) {
+        self.signing_key = None;
+        self.signed = false;
+    }
+
+    /// Checkpoints of this store are signed (on disk, or from the next
+    /// checkpoint because a key has been set).
+    pub fn is_signed(&self) -> bool {
+        self.signed
+    }
+
+    /// Check the checkpoint at `path` against the public key the caller
+    /// trusts; see [`signing::verify_store`]. Reads the file only: it works
+    /// on a store another process has open.
+    pub fn verify(path: &Path, trusted: &signing::VerifyingKey) -> Result<signing::VerifyReport> {
+        signing::verify_store(path, trusted)
+    }
+
     /// Flush current state to disk and truncate the WAL.
     ///
     /// Every code path that persists the full cache to the .h5 file must
@@ -685,10 +776,28 @@ impl HDF5Memory {
         // Record which WAL prefix this checkpoint contains, so a crash before
         // the truncate below can't replay those entries a second time.
         let wal_applied = self.wal.as_ref().map(|w| w.mark());
+        let signature = match &self.signing_key {
+            Some(key) => Some(signing::sign(
+                key,
+                &self.config,
+                &self.cache,
+                &self.sessions,
+                &self.knowledge,
+                wal_applied,
+            )),
+            None if self.signed => {
+                return Err(MemoryError::SigningKeyRequired(format!(
+                    "{} is signed; set its signing key before a checkpoint \
+                     (saves so far are held in the WAL or in memory)",
+                    self.config.path.display()
+                )));
+            }
+            None => None,
+        };
         // Written before the .h5 so a crash in between leaves a sidecar whose
         // generation matches no checkpoint (ignored), never the reverse.
         let ann_generation = self.persist_vector_index();
-        storage::write_to_disk_with_meta(
+        storage::write_to_disk_signed(
             &self.config.path,
             &self.config,
             &self.cache,
@@ -697,7 +806,9 @@ impl HDF5Memory {
             &schema::CheckpointMeta {
                 wal_applied,
                 ann_generation,
+                signed: signature.is_some(),
             },
+            signature.as_ref(),
         )?;
         if let Some(ref mut w) = self.wal {
             w.truncate()?;
@@ -826,6 +937,32 @@ impl HDF5Memory {
     // the index length drifts from the cache length (covering any mutation path
     // that doesn't call a hook, e.g. consolidation pushes).
 
+    /// Graph degree for the index, never below the 2 the builder requires:
+    /// a config value of 0 or 1 would otherwise panic inside `clawhdf5-ann`.
+    #[cfg(feature = "hnsw")]
+    fn hnsw_m(&self) -> usize {
+        self.config.hnsw_m.max(2)
+    }
+
+    /// Build-time candidate list size, never below the graph degree — a
+    /// smaller one cannot fill a node's connections.
+    #[cfg(feature = "hnsw")]
+    fn hnsw_ef_construction(&self) -> usize {
+        self.config.hnsw_ef_construction.max(self.hnsw_m())
+    }
+
+    /// Query-time candidate list size for a `k`-result search. `0` means the
+    /// default, which scales with `k`.
+    #[cfg(feature = "hnsw")]
+    pub(crate) fn hnsw_ef_search(&self, k: usize) -> usize {
+        let default = (k * 8).max(64);
+        if self.config.hnsw_ef_search == 0 {
+            default
+        } else {
+            self.config.hnsw_ef_search.max(k)
+        }
+    }
+
     /// How the index should store its copy of the vectors, per the config.
     #[cfg(feature = "hnsw")]
     fn index_storage(&self) -> Storage {
@@ -856,8 +993,8 @@ impl HDF5Memory {
         let rows: Vec<Vec<f32>> = self.cache.embeddings.iter().map(<[f32]>::to_vec).collect();
         let mut index = HnswIndex::build_with(
             &rows,
-            HNSW_M,
-            HNSW_EF_CONSTRUCTION,
+            self.hnsw_m(),
+            self.hnsw_ef_construction(),
             DistanceMetric::Cosine,
             self.index_storage(),
         );
@@ -962,6 +1099,18 @@ impl HDF5Memory {
         &self.config
     }
 
+    /// The sessions recorded in this store.
+    pub fn sessions(&self) -> &SessionCache {
+        &self.sessions
+    }
+
+    /// Mutable access to the sessions, e.g. to add many at once. Changes
+    /// reach the disk at the next checkpoint (any flushing call, such as
+    /// [`HDF5Memory::flush_wal`] or `save_batch`), not immediately.
+    pub fn sessions_mut(&mut self) -> &mut SessionCache {
+        &mut self.sessions
+    }
+
     /// Get a reference to the knowledge cache.
     pub fn knowledge(&self) -> &KnowledgeCache {
         &self.knowledge
@@ -1024,7 +1173,29 @@ impl HDF5Memory {
     /// Upsert: if an active entry with the same tags (key) exists, update it in-place.
     /// Otherwise append a new entry. Use this for key-based memory stores where
     /// the same key should not create duplicates.
+    /// A `float16` store holds embeddings as IEEE half precision, which has no
+    /// finite value beyond ±65504. Refuse such an embedding rather than
+    /// silently store infinity. (Values that are already infinite or NaN are
+    /// stored as they are, as in an `f32` store.)
+    fn check_embedding(&self, embedding: &[f32]) -> Result<()> {
+        if !self.config.float16 {
+            return Ok(());
+        }
+        let overflow = embedding
+            .iter()
+            .enumerate()
+            .find(|&(_, &v)| v.is_finite() && round_to_f16(v).is_infinite());
+        match overflow {
+            None => Ok(()),
+            Some((i, v)) => Err(MemoryError::InvalidEntry(format!(
+                "embedding[{i}] = {v} is outside the half-precision range (±65504) \
+                 of this float16 store"
+            ))),
+        }
+    }
+
     pub fn save_or_update(&mut self, entry: MemoryEntry) -> Result<usize> {
+        self.check_embedding(&entry.embedding)?;
         if let Some(existing_idx) = self.cache.find_by_tags(&entry.tags) {
             if let Some(ref mut w) = self.wal {
                 let wal_entry = wal::WalEntry {
@@ -1080,6 +1251,7 @@ impl HDF5Memory {
 
 impl AgentMemory for HDF5Memory {
     fn save(&mut self, entry: MemoryEntry) -> Result<usize> {
+        self.check_embedding(&entry.embedding)?;
         if let Some(ref mut w) = self.wal {
             let wal_entry = wal::WalEntry {
                 entry_type: wal::WalEntryType::Save,
@@ -1121,6 +1293,10 @@ impl AgentMemory for HDF5Memory {
     }
 
     fn save_batch(&mut self, entries: Vec<MemoryEntry>) -> Result<Vec<usize>> {
+        // All or nothing: check every entry before storing any.
+        for entry in &entries {
+            self.check_embedding(&entry.embedding)?;
+        }
         let mut indices = Vec::with_capacity(entries.len());
         for entry in entries {
             let idx = self.cache.push(
@@ -1281,6 +1457,9 @@ impl HDF5Memory {
         })?;
         let view = memory_strategy::CacheStoreView::new(&self.cache, &self.knowledge);
         let output = strat.evaluate(&exchange, &view);
+        for e in &output.entries {
+            self.check_embedding(&e.embedding)?;
+        }
         for e in &output.entries {
             self.cache.push(
                 e.chunk.clone(),
@@ -1305,6 +1484,35 @@ impl HDF5Memory {
 }
 
 impl HDF5Memory {
+    /// Delete many records with a single checkpoint, where
+    /// [`AgentMemory::delete`] checkpoints once per record.
+    ///
+    /// All or nothing: if any id is out of range or already deleted (or
+    /// repeated), nothing is deleted and `MemoryError::NotFound` is returned.
+    /// Unlike `delete`, this never auto-compacts, so the records stay in the
+    /// store as tombstones (their indices unchanged) until [`AgentMemory::compact`]
+    /// is called — importers use it to carry over records that were already
+    /// deleted in the source.
+    pub fn delete_batch(&mut self, ids: &[usize]) -> Result<()> {
+        let mut seen = std::collections::HashSet::with_capacity(ids.len());
+        for &id in ids {
+            if self.cache.tombstones.get(id).copied() != Some(0) || !seen.insert(id) {
+                return Err(MemoryError::NotFound(format!(
+                    "entry {id} not found or already deleted"
+                )));
+            }
+        }
+        if ids.is_empty() {
+            return Ok(());
+        }
+        for &id in ids {
+            self.cache.mark_deleted(id);
+            self.hnsw_on_delete(id);
+            self.bm25_on_delete(id);
+        }
+        self.flush()
+    }
+
     pub fn tick_session(&mut self) -> Result<()> {
         let d = self.config.decay_factor;
         for w in self.cache.activation_weights.iter_mut() {
@@ -1365,6 +1573,16 @@ impl HDF5Memory {
         let mut promoted = 0;
 
         for key in candidates {
+            // Check before taking, so a rejected entry stays in the ephemeral
+            // tier rather than being lost.
+            if let Some(emb) = self
+                .ephemeral
+                .as_ref()
+                .and_then(|s| s.get_entry(&key))
+                .and_then(|e| e.embedding.as_deref())
+            {
+                self.check_embedding(emb)?;
+            }
             let entry = match self
                 .ephemeral
                 .as_mut()
@@ -1493,6 +1711,79 @@ mod tests {
         }
     }
 
+    #[test]
+    fn delete_batch_tombstones_without_compacting() {
+        let dir = TempDir::new().unwrap();
+        let path = dir.path().join("test.h5");
+        let mut mem = HDF5Memory::create(make_config(&dir)).unwrap();
+        mem.save_batch(
+            (0..4)
+                .map(|i| make_entry(&format!("record {i}"), &[i as f32, 1.0, 0.0, 0.0]))
+                .collect(),
+        )
+        .unwrap();
+        // 3 of 4 is far past compact_threshold (0.3): delete() would compact.
+        mem.delete_batch(&[0, 1, 3]).unwrap();
+        assert_eq!(mem.count(), 4);
+        assert_eq!(mem.count_active(), 1);
+        drop(mem);
+
+        let mut mem = HDF5Memory::open(&path).unwrap();
+        assert_eq!(mem.cache.tombstones, vec![1, 1, 0, 1]);
+        let hits = mem.hybrid_search(&[0.0, 1.0, 0.0, 0.0], "record", 0.5, 0.5, 10);
+        assert!(
+            hits.iter().all(|r| r.index == 2),
+            "tombstoned record returned"
+        );
+    }
+
+    #[test]
+    fn delete_batch_is_all_or_nothing() {
+        let dir = TempDir::new().unwrap();
+        let mut mem = HDF5Memory::create(make_config(&dir)).unwrap();
+        mem.save_batch(vec![
+            make_entry("a", &[1.0, 0.0, 0.0, 0.0]),
+            make_entry("b", &[0.0, 1.0, 0.0, 0.0]),
+        ])
+        .unwrap();
+        for bad in [&[0, 5][..], &[1, 1][..]] {
+            assert!(matches!(
+                mem.delete_batch(bad),
+                Err(MemoryError::NotFound(_))
+            ));
+            assert_eq!(mem.count_active(), 2, "{bad:?} deleted something");
+        }
+        mem.delete_batch(&[]).unwrap();
+        assert_eq!(mem.count_active(), 2);
+    }
+
+    #[test]
+    fn sessions_mut_add_at_keeps_timestamp_across_reopen() {
+        let dir = TempDir::new().unwrap();
+        let path = dir.path().join("test.h5");
+        let mut mem = HDF5Memory::create(make_config(&dir)).unwrap();
+        mem.sessions_mut()
+            .add_at("s-old", 2, 7, "discord", "old summary", 1.7e15);
+        mem.flush_wal().unwrap();
+        drop(mem);
+
+        let mem = HDF5Memory::open_read_only(&path).unwrap();
+        let s = mem.sessions();
+        assert_eq!(s.len(), 1);
+        let e = &s.entries[0];
+        assert_eq!(
+            (
+                e.id.as_str(),
+                e.start_idx,
+                e.end_idx,
+                e.channel.as_str(),
+                e.ts
+            ),
+            ("s-old", 2, 7, "discord", 1.7e15)
+        );
+        assert_eq!(s.summaries[0], "old summary");
+    }
+
     #[test]
     fn create_new_file() {
         let dir = TempDir::new().unwrap();

crates/clawhdf5-agent/src/openclaw.rs

@@ -1,10 +1,12 @@
-//! OpenClaw Integration Layer.
+//! A Markdown-oriented memory backend over [`crate::HDF5Memory`].
 //!
-//! Bridge between OpenClaw agent gateway (Markdown + sqlite-vec) and the
-//! clawhdf5 HDF5-backed memory backend.  Provides:
+//! Named for OpenClaw, whose workspace memory is Markdown, but **not an
+//! OpenClaw plugin**: nothing here registers with OpenClaw, and the
+//! integration it was written for never worked (see `docs/openclaw.md`).
+//! Provides:
 //!
-//! - [`MemoryBackend`] — the trait OpenClaw implements against.
-//! - [`ClawhdfBackend`] — concrete HDF5-backed implementation.
+//! - [`MemoryBackend`] — search / read back / write / ingest / export.
+//! - [`ClawhdfBackend`] — the HDF5-backed implementation.
 //! - [`MarkdownParser`] — splits Markdown into [`MarkdownSection`] records.
 //! - [`MarkdownExporter`] — renders sections back to Markdown text.
 
@@ -13,9 +15,8 @@ use std::path::{Path, PathBuf};
 use std::time::{SystemTime, UNIX_EPOCH};
 
 use crate::{
-    AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry,
-    confidence::{ConfidenceConfig, ScoredResult, reject_low_confidence},
-    reranker::{ReRankConfig, RerankInput, rerank},
+    AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry, SearchOptions,
+    confidence::ConfidenceConfig, reranker::ReRankConfig,
 };
 
 // ─────────────────────────────────────────────────────────────────────────────
@@ -62,7 +63,8 @@ pub struct BackendStats {
 // MemoryBackend trait
 // ─────────────────────────────────────────────────────────────────────────────
 
-/// Interface that OpenClaw uses to interact with a memory backend.
+/// A Markdown-oriented memory backend: search, read back by path, write,
+/// ingest and export.
 ///
 /// Implementors provide persistent storage, full-text + vector search,
 /// Markdown ingestion / export, and statistics.
@@ -319,7 +321,7 @@ impl MarkdownExporter {
 ///
 /// # Path mapping
 ///
-/// OpenClaw addresses memories by file path (e.g. `"memory/user.md"`).
+/// Memories are addressed by file path (e.g. `"memory/user.md"`).
 /// Internally every [`MemoryEntry`] stores the originating path as its
 /// `source_channel`.  Section sub-paths are stored as
 /// `"<path>::<heading>"`.
@@ -422,7 +424,7 @@ impl ClawhdfBackend {
 
     // ── Compaction & Consolidation hooks (7.6) ────────────────────────────
 
-    /// Run a compaction cycle — called by OpenClaw during session compaction.
+    /// Run a compaction cycle (decay, compaction, WAL flush).
     ///
     /// Sequence:
     /// 1. `tick_session()` — apply Hebbian decay to all activation weights.
@@ -524,71 +526,27 @@ impl ClawhdfBackend {
 
 impl MemoryBackend for ClawhdfBackend {
     /// Search using hybrid vector + BM25 retrieval, then re-rank and
-    /// confidence-filter.
+    /// confidence-filter — [`HDF5Memory::search`] with both stages on.
     fn search(
         &mut self,
         query_text: &str,
         query_embedding: &[f32],
         k: usize,
     ) -> Vec<MemorySearchResult> {
-        // 1. Hybrid retrieval (vector + BM25, fused by score).
-        let candidates = k.saturating_mul(3).max(10);
-        let raw = self.memory.hybrid_search_with(
-            query_embedding,
-            query_text,
-            crate::hybrid::DEFAULT_FUSION,
-            candidates,
-        );
-
-        if raw.is_empty() {
-            return Vec::new();
-        }
-
-        let now = Self::now_secs();
-
-        // 2. Re-rank using temporal recency, source authority, Hebbian weight.
-        let rerank_inputs: Vec<RerankInput> = raw
-            .iter()
-            .map(|r| RerankInput {
-                index: r.index,
-                timestamp: r.timestamp,
-                source_channel: r.source_channel.clone(),
-                raw_activation: r.activation,
-                relevance: r.score,
-            })
-            .collect();
-
-        let reranked = rerank(&rerank_inputs, &self.rerank_config, now);
-
-        // 3. Confidence rejection.
-        let scored: Vec<ScoredResult> = reranked
-            .iter()
-            .map(|r| ScoredResult {
-                index: r.index,
-                score: r.combined_score,
-            })
-            .collect();
-
-        let confident = reject_low_confidence(&scored, &self.confidence_config);
-
-        // 4. Map back to MemorySearchResult; preserve raw text via index lookup.
-        let raw_by_idx: HashMap<usize, &crate::SearchResult> =
-            raw.iter().map(|r| (r.index, r)).collect();
-
-        confident
+        let options = SearchOptions::new(k)
+            .with_rerank(self.rerank_config)
+            .with_confidence(self.confidence_config.clone())
+            .at_time(Self::now_secs());
+        self.memory
+            .search(query_embedding, query_text, &options)
             .into_iter()
-            .take(k)
-            .filter_map(|sr| {
-                let r = raw_by_idx.get(&sr.index)?;
-                let path = r.source_channel.clone();
-                Some(MemorySearchResult {
-                    text: r.chunk.clone(),
-                    score: sr.score,
-                    path: path.clone(),
+            .map(|r| MemorySearchResult {
+                text: r.chunk,
+                score: r.score,
+                path: r.source_channel.clone(),
                 line_range: None,
                 timestamp: Some(r.timestamp),
-                    source: path,
-                })
+                source: r.source_channel,
             })
             .collect()
     }

crates/clawhdf5-agent/src/provenance.rs

@@ -2,7 +2,7 @@
 //!
 //! Records the origin, authorship, and a content hash of every memory chunk
 //! so the system can detect *accidental* corruption and trace data lineage.
-//! The hash is unkeyed (see [`fnv1a_64`]) — this is not a tamper-evidence or
+//! The hash is unkeyed (FNV-1a) — this is not a tamper-evidence or
 //! authenticity guarantee.
 
 use std::collections::HashMap;

crates/clawhdf5-agent/src/schema.rs

@@ -15,6 +15,9 @@ use crate::session::SessionCache;
 use crate::wal::WalMark;
 
 pub const SCHEMA_VERSION: &str = "1.0";
+/// Writer-version tag stored in `/meta` as `edgehdf5_version`. Kept for file
+/// compatibility; despite the name it has nothing to do with ZeroClaw, which
+/// does not use clawhdf5.
 pub const ZEROCLAW_VERSION: &str = "0.8.0";
 
 /// `/meta` attributes holding the [`WalMark`] of the WAL prefix already folded
@@ -23,6 +26,7 @@ pub const ZEROCLAW_VERSION: &str = "0.8.0";
 const WAL_APPLIED_LEN_ATTR: &str = "wal_applied_len";
 const WAL_APPLIED_CRC_ATTR: &str = "wal_applied_crc";
 const ANN_GENERATION_ATTR: &str = "ann_generation";
+const SIG_VERSION_ATTR: &str = "sig_version";
 
 /// Build a complete HDF5 file from the in-memory state.
 pub fn build_hdf5_file(
@@ -46,7 +50,7 @@ pub fn build_hdf5_file_with_mark(
 ) -> Result<Vec<u8>, MemoryError> {
     let meta = CheckpointMeta {
         wal_applied,
-        ann_generation: None,
+        ..CheckpointMeta::default()
     };
     build_hdf5_file_with_meta(config, cache, sessions, knowledge, &meta)
 }
@@ -61,6 +65,10 @@ pub struct CheckpointMeta {
     /// one left over from another checkpoint can never be attached to records
     /// it wasn't built from.
     pub ann_generation: Option<u64>,
+    /// The checkpoint carries an Ed25519 signature (see [`crate::signing`]).
+    /// Read-only: whether a checkpoint is *written* signed is decided by the
+    /// signature passed to [`build_hdf5_file_signed`].
+    pub signed: bool,
 }
 
 /// [`build_hdf5_file`] with checkpoint bookkeeping.
@@ -70,6 +78,19 @@ pub fn build_hdf5_file_with_meta(
     sessions: &SessionCache,
     knowledge: &KnowledgeCache,
     checkpoint: &CheckpointMeta,
+) -> Result<Vec<u8>, MemoryError> {
+    build_hdf5_file_signed(config, cache, sessions, knowledge, checkpoint, None)
+}
+
+/// [`build_hdf5_file_with_meta`], plus a signed manifest of the contents
+/// (see [`crate::signing`]).
+pub fn build_hdf5_file_signed(
+    config: &MemoryConfig,
+    cache: &MemoryCache,
+    sessions: &SessionCache,
+    knowledge: &KnowledgeCache,
+    checkpoint: &CheckpointMeta,
+    signature: Option<&crate::signing::StoredSignature>,
 ) -> Result<Vec<u8>, MemoryError> {
     let wal_applied = checkpoint.wal_applied;
     let mut builder = clawhdf5::FileBuilder::new();
@@ -108,6 +129,15 @@ pub fn build_hdf5_file_with_meta(
         "quantized_index",
         AttrValue::I64(config.quantized_index.into()),
     );
+    meta.set_attr("hnsw_m", AttrValue::I64(config.hnsw_m as i64));
+    meta.set_attr(
+        "hnsw_ef_construction",
+        AttrValue::I64(config.hnsw_ef_construction as i64),
+    );
+    meta.set_attr(
+        "hnsw_ef_search",
+        AttrValue::I64(config.hnsw_ef_search as i64),
+    );
     meta.set_attr(
         "edgehdf5_version",
         AttrValue::String(ZEROCLAW_VERSION.into()),
@@ -121,11 +151,42 @@ pub fn build_hdf5_file_with_meta(
         // round trip through every reader.
         meta.set_attr(ANN_GENERATION_ATTR, AttrValue::I64(generation as i64));
     }
+    if let Some(sig) = signature {
+        use crate::signing::to_hex;
+        let m = &sig.manifest;
+        meta.set_attr(
+            SIG_VERSION_ATTR,
+            AttrValue::I64(crate::signing::MANIFEST_VERSION),
+        );
+        meta.set_attr("sig_algorithm", AttrValue::String("ed25519".into()));
+        meta.set_attr("sig_public_key", AttrValue::String(to_hex(&sig.public_key)));
+        meta.set_attr("sig_signature", AttrValue::String(to_hex(&sig.signature)));
+        meta.set_attr("sig_record_count", AttrValue::I64(m.record_count as i64));
+        meta.set_attr(
+            "sig_records_root",
+            AttrValue::String(to_hex(&m.records_root)),
+        );
+        meta.set_attr("sig_settings", AttrValue::String(to_hex(&m.settings)));
+        meta.set_attr("sig_sessions", AttrValue::String(to_hex(&m.sessions)));
+        meta.set_attr("sig_graph", AttrValue::String(to_hex(&m.graph)));
+    }
     // Need at least one dataset in the group for it to be a proper group
     meta.create_dataset("_marker").with_u8_data(&[1]).compact();
     let finished_meta = meta.finish();
     builder.add_group(finished_meta);
 
+    // /integrity: the signed per-record hashes, so verification can say
+    // which records changed.
+    if let Some(sig) = signature {
+        let mut group = builder.create_group("integrity");
+        let flat: Vec<u8> = sig.record_hashes.iter().flatten().copied().collect();
+        group
+            .create_dataset("record_hashes")
+            .with_u8_data(&flat)
+            .with_shape(&[sig.record_hashes.len() as u64, 32]);
+        builder.add_group(group.finish());
+    }
+
     // /memory group
     build_memory_group(&mut builder, config, cache)?;
 
@@ -150,20 +211,27 @@ fn build_memory_group(
     // chunks: fixed-length string array
     write_string_dataset(&mut group, "chunks", &cache.chunks);
 
-    // embeddings: f32 [N x D]
+    // embeddings: [N x D], f32 — or IEEE half precision for a `float16`
+    // store. The cache already holds half-rounded values then, so this
+    // conversion is exact and a reopened store sees the same numbers.
     let n = cache.embeddings.len() as u64;
     let d = cache.embedding_dim as u64;
     let flat = cache.flat_embeddings();
     {
-        let ds = group
-            .create_dataset("embeddings")
-            .with_f32_data(flat)
-            .with_shape(&[n, d]);
+        let ds = group.create_dataset("embeddings");
+        let elem_bytes: u64 = if config.float16 {
+            ds.with_f16_data(flat);
+            2
+        } else {
+            ds.with_f32_data(flat);
+            4
+        };
+        ds.with_shape(&[n, d]);
 
         // Chunk size tuning: target ~256KB per chunk for optimal I/O
         if n > 0 && d > 0 {
             let target_chunk_bytes: u64 = 256 * 1024;
-            let rows_per_chunk = (target_chunk_bytes / (d * 4)).max(1).min(n);
+            let rows_per_chunk = (target_chunk_bytes / (d * elem_bytes)).max(1).min(n);
             ds.with_chunks(&[rows_per_chunk, d]);
 
             // Compression. Shuffle is applied automatically (auto-shuffle
@@ -409,10 +477,34 @@ fn write_string_dataset(
     }
 }
 
+/// `/meta`'s attributes, failing if any of them cannot be read.
+///
+/// `Group::attrs` leaves out an attribute it cannot decode. For the store's
+/// settings that would silently fall back to defaults (e.g. `float16`, the
+/// WAL mark), so an unreadable attribute is an error here, as it was before
+/// `attrs` became tolerant.
+fn meta_attrs(
+    file: &clawhdf5::File,
+) -> Result<std::collections::HashMap<String, AttrValue>, MemoryError> {
+    let meta = file
+        .group("meta")
+        .map_err(|e| MemoryError::Schema(format!("missing /meta group: {e}")))?;
+    let (attrs, errors) = meta
+        .attrs_with_errors()
+        .map_err(|e| MemoryError::Schema(format!("cannot read /meta attrs: {e}")))?;
+    if let Some(e) = errors.first() {
+        return Err(MemoryError::Schema(format!(
+            "cannot read /meta attrs: {} unreadable, first: {e}",
+            errors.len()
+        )));
+    }
+    Ok(attrs)
+}
+
 /// Validate an HDF5 file has the correct schema and load all data.
 /// Read the checkpoint's [`WalMark`] from `/meta`, if it has one.
 pub fn read_wal_mark(file: &clawhdf5::File) -> Option<WalMark> {
-    let attrs = file.group("meta").ok()?.attrs().ok()?;
+    let attrs = meta_attrs(file).ok()?;
     let len = match attrs.get(WAL_APPLIED_LEN_ATTR)? {
         AttrValue::I64(v) => u64::try_from(*v).ok()?,
         _ => return None,
@@ -424,19 +516,75 @@ pub fn read_wal_mark(file: &clawhdf5::File) -> Option<WalMark> {
     Some(WalMark { len, crc })
 }
 
+/// Read a checkpoint's signature, if it has one. A signature whose
+/// attributes are present but malformed is an error, not "unsigned".
+pub fn read_signature(
+    file: &clawhdf5::File,
+) -> Result<Option<crate::signing::StoredSignature>, MemoryError> {
+    use crate::signing::{Manifest, StoredSignature, from_hex};
+    let attrs = meta_attrs(file)?;
+    let version = match attrs.get(SIG_VERSION_ATTR) {
+        None => return Ok(None),
+        Some(AttrValue::I64(v)) => *v,
+        Some(_) => return Err(MemoryError::Schema("malformed sig_version".into())),
+    };
+    if version != crate::signing::MANIFEST_VERSION {
+        return Err(MemoryError::Schema(format!(
+            "unsupported signature version {version}"
+        )));
+    }
+    fn hex<const N: usize>(
+        attrs: &std::collections::HashMap<String, AttrValue>,
+        name: &str,
+    ) -> Result<[u8; N], MemoryError> {
+        match attrs.get(name) {
+            Some(AttrValue::String(s)) => from_hex::<N>(s),
+            _ => None,
+        }
+        .ok_or_else(|| MemoryError::Schema(format!("malformed or missing {name}")))
+    }
+    let record_count = match attrs.get("sig_record_count") {
+        Some(AttrValue::I64(v)) if *v >= 0 => *v as u64,
+        _ => return Err(MemoryError::Schema("malformed sig_record_count".into())),
+    };
+    let group = file
+        .group("integrity")
+        .map_err(|e| MemoryError::Schema(format!("signed checkpoint without /integrity: {e}")))?;
+    let flat = read_u8_dataset(&group, "record_hashes")?;
+    if flat.len() % 32 != 0 {
+        return Err(MemoryError::Schema(
+            "/integrity/record_hashes is not a whole number of hashes".into(),
+        ));
+    }
+    let record_hashes = flat.as_chunks::<32>().0.to_vec();
+    Ok(Some(StoredSignature {
+        manifest: Manifest {
+            record_count,
+            records_root: hex::<32>(&attrs, "sig_records_root")?,
+            settings: hex::<32>(&attrs, "sig_settings")?,
+            sessions: hex::<32>(&attrs, "sig_sessions")?,
+            graph: hex::<32>(&attrs, "sig_graph")?,
+        },
+        record_hashes,
+        public_key: hex::<32>(&attrs, "sig_public_key")?,
+        signature: hex::<64>(&attrs, "sig_signature")?,
+    }))
+}
+
 /// Read the checkpoint bookkeeping from `/meta`.
 pub fn read_checkpoint_meta(file: &clawhdf5::File) -> CheckpointMeta {
-    let ann_generation = file
-        .group("meta")
+    let ann_generation =
+        meta_attrs(file)
             .ok()
-        .and_then(|g| g.attrs().ok())
             .and_then(|attrs| match attrs.get(ANN_GENERATION_ATTR) {
                 Some(AttrValue::I64(v)) => Some(*v as u64),
                 _ => None,
             });
+    let signed = meta_attrs(file).is_ok_and(|attrs| attrs.contains_key(SIG_VERSION_ATTR));
     CheckpointMeta {
         wal_applied: read_wal_mark(file),
         ann_generation,
+        signed,
     }
 }
 
@@ -444,12 +592,7 @@ pub fn validate_and_load(
     file: &clawhdf5::File,
 ) -> Result<(MemoryConfig, MemoryCache, SessionCache, KnowledgeCache), MemoryError> {
     // Read /meta group attributes
-    let meta = file
-        .group("meta")
-        .map_err(|e| MemoryError::Schema(format!("missing /meta group: {e}")))?;
-    let attrs = meta
-        .attrs()
-        .map_err(|e| MemoryError::Schema(format!("cannot read /meta attrs: {e}")))?;
+    let attrs = meta_attrs(file)?;
 
     let schema_version = match attrs.get("schema_version") {
         Some(AttrValue::String(s)) => s.clone(),
@@ -488,11 +631,32 @@ pub fn validate_and_load(
         wal_max_entries: optional_i64_attr(&attrs, "wal_max_entries")
             .and_then(|v| usize::try_from(v).ok())
             .unwrap_or(500),
+        // `false`, not the new-store default: a store written before this
+        // setting existed was built with an f32 index, and reopening it must
+        // not silently change that.
         quantized_index: optional_bool_attr(&attrs, "quantized_index", false),
+        hnsw_m: optional_i64_attr(&attrs, "hnsw_m")
+            .and_then(|v| usize::try_from(v).ok())
+            .unwrap_or(16),
+        hnsw_ef_construction: optional_i64_attr(&attrs, "hnsw_ef_construction")
+            .and_then(|v| usize::try_from(v).ok())
+            .unwrap_or(64),
+        hnsw_ef_search: optional_i64_attr(&attrs, "hnsw_ef_search")
+            .and_then(|v| usize::try_from(v).ok())
+            .unwrap_or(0),
     };
 
     // Load /memory group
-    let memory_cache = load_memory_group(file, embedding_dim)?;
+    let mut memory_cache = load_memory_group(file, embedding_dim)?;
+    // A float16 store's cache holds half-rounded embeddings. Embeddings read
+    // from an f16 dataset already are; a float16 store whose last checkpoint
+    // predates half-precision storage is still f32 on disk and is rounded
+    // here.
+    if config.float16 && embeddings_are_f16(file) {
+        memory_cache.half_precision = true;
+    } else {
+        memory_cache.set_half_precision(config.float16);
+    }
 
     // Load /sessions group
     let session_cache = load_sessions_group(file)?;
@@ -735,6 +899,13 @@ fn read_string_dataset_from_group(
         .map_err(|e| MemoryError::Hdf5(format!("cannot read strings from {name}: {e}")))
 }
 
+/// Whether `/memory/embeddings` is stored as IEEE half precision.
+fn embeddings_are_f16(file: &clawhdf5::File) -> bool {
+    file.dataset("memory/embeddings")
+        .and_then(|ds| ds.dtype())
+        .is_ok_and(|dt| matches!(dt, clawhdf5::DType::Other(ref s) if s == "float16"))
+}
+
 fn read_f32_dataset(group: &clawhdf5::Group<'_>, name: &str) -> Result<Vec<f32>, MemoryError> {
     let ds = group
         .dataset(name)

crates/clawhdf5-agent/src/search.rs

@@ -2,18 +2,107 @@
 
 use std::path::Path;
 
+use std::collections::HashSet;
+
 use crate::bm25;
+use crate::confidence::{ConfidenceConfig, ScoredResult, reject_low_confidence};
 use crate::hybrid;
+use crate::reranker::{ReRankConfig, RerankInput, rerank};
 use crate::{HDF5Memory, MAX_ACTIVATION_WEIGHT, MemoryError, Result, SearchResult};
 
+/// Options for [`HDF5Memory::search`].
+///
+/// [`SearchOptions::new`] is plain hybrid search with the tuned default
+/// fusion — the same as `hybrid_search_with(.., hybrid::DEFAULT_FUSION, k)`.
+/// Every stage beyond that is opt-in.
+#[derive(Debug, Clone)]
+pub struct SearchOptions {
+    /// Number of results to return.
+    pub k: usize,
+    /// How the vector and keyword stages are combined.
+    pub fusion: hybrid::Fusion,
+    /// Only consider records whose `source_channel` is one of these. The
+    /// filter applies *before* ranking, so a filtered search still returns up
+    /// to `k` results and scores are normalised over the records it can
+    /// return. `None` searches everything; an empty list matches nothing.
+    pub source_channels: Option<Vec<String>>,
+    /// Re-rank a candidate pool by retrieval relevance, recency, source
+    /// authority and activation — the pipeline the OpenClaw backend runs.
+    pub rerank: Option<ReRankConfig>,
+    /// Candidates retrieved for re-ranking; 0 means `max(3k, 10)`.
+    pub rerank_pool: usize,
+    /// Drop low-confidence results (after re-ranking, when that is on).
+    pub confidence: Option<ConfidenceConfig>,
+    /// The time recency is measured from, in seconds since the epoch.
+    /// `None` uses the system clock.
+    pub now: Option<f64>,
+}
+
+impl SearchOptions {
+    pub fn new(k: usize) -> Self {
+        Self {
+            k,
+            fusion: hybrid::DEFAULT_FUSION,
+            source_channels: None,
+            rerank: None,
+            rerank_pool: 0,
+            confidence: None,
+            now: None,
+        }
+    }
+
+    pub fn with_fusion(mut self, fusion: hybrid::Fusion) -> Self {
+        self.fusion = fusion;
+        self
+    }
+
+    /// Search only records from these source channels.
+    pub fn with_sources<S: Into<String>>(mut self, channels: impl IntoIterator<Item = S>) -> Self {
+        self.source_channels = Some(channels.into_iter().map(Into::into).collect());
+        self
+    }
+
+    pub fn with_rerank(mut self, config: ReRankConfig) -> Self {
+        self.rerank = Some(config);
+        self
+    }
+
+    pub fn with_confidence(mut self, config: ConfidenceConfig) -> Self {
+        self.confidence = Some(config);
+        self
+    }
+
+    /// Measure recency from `now` (seconds since the epoch) instead of the
+    /// system clock — for reproducible results and tests.
+    pub fn at_time(mut self, now: f64) -> Self {
+        self.now = Some(now);
+        self
+    }
+}
+
+impl Default for SearchOptions {
+    fn default() -> Self {
+        Self::new(10)
+    }
+}
+
 impl HDF5Memory {
-    /// Vector + keyword scoring stage of [`HDF5Memory::hybrid_search`].
+    /// Vector + keyword scoring stage of [`HDF5Memory::search`].
     ///
     /// Without the `hnsw` feature this is a full linear cosine scan (the exact
     /// previous behaviour, also used as the correctness oracle in tests). With
     /// `hnsw` enabled and an index available, the vector candidates come from an
     /// approximate-nearest-neighbour search over an over-fetched pool, then merge
     /// with BM25 via the shared [`hybrid::merge_vector_keyword`].
+    ///
+    /// `exclude`, when given, marks records that must not be returned (1 =
+    /// excluded; it covers tombstones too). The index is over-fetched in
+    /// proportion to how much the mask removes. Surfacing `pool` candidates
+    /// costs the index roughly `pool × M` distance evaluations, while an exact
+    /// scan of the allowed records costs one each — so whenever that scan is
+    /// the cheaper of the two it is used instead, and it is also the fallback
+    /// if the pool comes back with too few allowed hits (the allowed records
+    /// sit away from the query). A filtered search never comes back short.
     #[cfg(feature = "hnsw")]
     fn vector_keyword_search(
         &mut self,
@@ -22,14 +111,32 @@ impl HDF5Memory {
         bm25: &bm25::BM25Index,
         fusion: hybrid::Fusion,
         k: usize,
+        exclude: Option<&[u8]>,
     ) -> Vec<(usize, f32)> {
         self.ensure_hnsw_fresh();
+        let n = self.cache.len();
+        // Over-fetch so the merge sees a useful vector pool. `ef` is
+        // configurable, but the pool the fusion stage sees is not tied to it:
+        // a caller lowering `ef` for speed should not silently narrow what
+        // fusion has to work with.
+        let mut pool = (k * 8).max(64);
+        let mut allowed = n;
+        if let Some(ex) = exclude {
+            allowed = ex.iter().filter(|&&e| e == 0).count();
+            if allowed == 0 {
+                return Vec::new();
+            }
+            // Expect `pool` allowed hits if the filter is independent of the
+            // query's neighbourhood.
+            pool = pool.saturating_mul(n).div_ceil(allowed);
+            if allowed <= pool.saturating_mul(self.hnsw_m()) {
+                return self.exact_masked_search(query_embedding, query_text, bm25, fusion, k, ex);
+            }
+        }
         match self.hnsw.as_ref() {
             Some(index) if !index.is_empty() && index.dimension() == query_embedding.len() => {
-                // Over-fetch so the merge sees a useful vector pool; cosine
-                // distance from the index converts back to similarity (1 - d).
-                let pool = (k * 8).max(64);
-                let candidates = index.search(query_embedding, pool, pool);
+                let ef = self.hnsw_ef_search(k).max(pool);
+                let candidates = index.search(query_embedding, pool, ef);
                 // A quantised index returns approximate distances, and no
                 // amount of `ef` fixes that — the loss is in the distances,
                 // not the graph. Re-score the pool against the cache's exact
@@ -38,6 +145,7 @@ impl HDF5Memory {
                 let exact = index.storage() == clawhdf5_ann::Storage::Int8;
                 let vec_scores: Vec<(usize, f32)> = candidates
                     .into_iter()
+                    .filter(|(id, _)| exclude.is_none_or(|ex| ex[*id] == 0))
                     .map(|(id, dist)| {
                         let score = if exact {
                             crate::vector_search::cosine_similarity(
@@ -52,10 +160,54 @@ impl HDF5Memory {
                     .collect();
                 // Fusion normalises over every keyword match, so it needs all
                 // the scores — but not ranked.
-                let kw_scores = bm25.scores(query_text);
+                let mut kw_scores = bm25.scores(query_text);
+                if let Some(ex) = exclude {
+                    if vec_scores.len() < k.min(allowed) {
+                        // The allowed records are not where the index looked.
+                        return self.exact_masked_search(
+                            query_embedding,
+                            query_text,
+                            bm25,
+                            fusion,
+                            k,
+                            ex,
+                        );
+                    }
+                    kw_scores.retain(|(id, _)| ex[*id] == 0);
+                }
                 hybrid::fuse(vec_scores, kw_scores, fusion, k)
             }
-            _ => hybrid::hybrid_search_fused(
+            _ => match exclude {
+                Some(ex) => {
+                    self.exact_masked_search(query_embedding, query_text, bm25, fusion, k, ex)
+                }
+                None => hybrid::hybrid_search_fused(
+                    query_embedding,
+                    query_text,
+                    &self.cache.embeddings,
+                    &self.cache.chunks,
+                    &self.cache.tombstones,
+                    bm25,
+                    fusion,
+                    k,
+                ),
+            },
+        }
+    }
+
+    #[cfg(not(feature = "hnsw"))]
+    fn vector_keyword_search(
+        &mut self,
+        query_embedding: &[f32],
+        query_text: &str,
+        bm25: &bm25::BM25Index,
+        fusion: hybrid::Fusion,
+        k: usize,
+        exclude: Option<&[u8]>,
+    ) -> Vec<(usize, f32)> {
+        match exclude {
+            Some(ex) => self.exact_masked_search(query_embedding, query_text, bm25, fusion, k, ex),
+            None => hybrid::hybrid_search_fused(
                 query_embedding,
                 query_text,
                 &self.cache.embeddings,
@@ -68,25 +220,33 @@ impl HDF5Memory {
         }
     }
 
-    #[cfg(not(feature = "hnsw"))]
-    fn vector_keyword_search(
-        &mut self,
+    /// Exact hybrid search over the records `exclude` leaves (0 = allowed).
+    fn exact_masked_search(
+        &self,
         query_embedding: &[f32],
         query_text: &str,
         bm25: &bm25::BM25Index,
         fusion: hybrid::Fusion,
         k: usize,
+        exclude: &[u8],
     ) -> Vec<(usize, f32)> {
-        hybrid::hybrid_search_fused(
-            query_embedding,
-            query_text,
-            &self.cache.embeddings,
-            &self.cache.chunks,
-            &self.cache.tombstones,
-            bm25,
-            fusion,
-            k,
-        )
+        let vec_scores =
+            hybrid::exact_vector_scores(query_embedding, &self.cache.embeddings, exclude);
+        let mut kw_scores = bm25.scores(query_text);
+        kw_scores.retain(|(id, _)| exclude.get(*id) == Some(&0));
+        hybrid::fuse(vec_scores, kw_scores, fusion, k)
+    }
+
+    /// The exclusion mask for a source-channel filter: 1 for a tombstoned
+    /// record or one from a channel not in `channels`.
+    fn source_mask(&self, channels: &[String]) -> Vec<u8> {
+        let allowed: HashSet<&str> = channels.iter().map(String::as_str).collect();
+        self.cache
+            .source_channels
+            .iter()
+            .zip(&self.cache.tombstones)
+            .map(|(ch, &t)| u8::from(t != 0 || !allowed.contains(ch.as_str())))
+            .collect()
     }
 
     /// Perform hybrid search combining cosine vector similarity and BM25 keyword search.
@@ -121,12 +281,53 @@ impl HDF5Memory {
         fusion: hybrid::Fusion,
         k: usize,
     ) -> Vec<SearchResult> {
+        self.search(
+            query_embedding,
+            query_text,
+            &SearchOptions::new(k).with_fusion(fusion),
+        )
+    }
+
+    /// Hybrid search with optional source filtering, re-ranking and
+    /// confidence rejection — see [`SearchOptions`].
+    ///
+    /// Stages, in order: vector + keyword retrieval over the records the
+    /// source filter allows; fusion; scaling by Hebbian activation; re-ranking
+    /// (if on) of a `rerank_pool` of candidates; confidence rejection (if on);
+    /// the top `k`. The records returned with a positive score get their
+    /// Hebbian boost.
+    pub fn search(
+        &mut self,
+        query_embedding: &[f32],
+        query_text: &str,
+        options: &SearchOptions,
+    ) -> Vec<SearchResult> {
+        let k = options.k;
+        let fetch = match options.rerank {
+            Some(_) if options.rerank_pool > 0 => options.rerank_pool.max(k),
+            Some(_) => k.saturating_mul(3).max(10),
+            None => k,
+        };
+        let exclude = options
+            .source_channels
+            .as_deref()
+            .map(|channels| self.source_mask(channels));
+
         // The keyword index lives for the life of the store and is updated
         // incrementally. Take it out for the duration of the call so the
         // vector stage can borrow `self` mutably, then put it back.
         self.ensure_bm25_fresh();
         let bm25 = self.bm25.take().expect("ensure_bm25_fresh leaves an index");
-        let scored = self.vector_keyword_search(query_embedding, query_text, &bm25, fusion, k);
+        let scored = self.vector_keyword_search(
+            query_embedding,
+            query_text,
+            &bm25,
+            options.fusion,
+            fetch,
+            exclude.as_deref(),
+        );
+        self.bm25 = Some(bm25);
+
         let mut results: Vec<SearchResult> = scored
             .into_iter()
             .map(|(idx, score)| {
@@ -150,6 +351,25 @@ impl HDF5Memory {
                 .then(a.index.cmp(&b.index))
         });
 
+        if let Some(config) = &options.rerank {
+            results = Self::rerank_results(results, config, options.now);
+        }
+        if let Some(config) = &options.confidence {
+            let scored: Vec<ScoredResult> = results
+                .iter()
+                .map(|r| ScoredResult {
+                    index: r.index,
+                    score: r.score,
+                })
+                .collect();
+            let keep: HashSet<usize> = reject_low_confidence(&scored, config)
+                .into_iter()
+                .map(|r| r.index)
+                .collect();
+            results.retain(|r| keep.contains(&r.index));
+        }
+        results.truncate(k);
+
         // Only reinforce records that actually matched. When fewer than `k`
         // records are relevant, the rest of the list is zero-score filler;
         // boosting it would teach the store that arbitrary records are
@@ -160,11 +380,45 @@ impl HDF5Memory {
             .map(|r| r.index)
             .collect();
         self.apply_hebbian_boost(&hit_indices);
-        self.bm25 = Some(bm25);
 
         results
     }
 
+    /// Reorder by the re-ranker's combined score, which also becomes each
+    /// result's `score`.
+    fn rerank_results(
+        results: Vec<SearchResult>,
+        config: &ReRankConfig,
+        now: Option<f64>,
+    ) -> Vec<SearchResult> {
+        let now = now.unwrap_or_else(|| {
+            std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .map(|d| d.as_secs_f64())
+                .unwrap_or(0.0)
+        });
+        let inputs: Vec<RerankInput> = results
+            .iter()
+            .map(|r| RerankInput {
+                index: r.index,
+                timestamp: r.timestamp,
+                source_channel: r.source_channel.clone(),
+                raw_activation: r.activation,
+                relevance: r.score,
+            })
+            .collect();
+        let mut by_index: std::collections::HashMap<usize, SearchResult> =
+            results.into_iter().map(|r| (r.index, r)).collect();
+        rerank(&inputs, config, now)
+            .into_iter()
+            .filter_map(|rr| {
+                let mut r = by_index.remove(&rr.index)?;
+                r.score = rr.combined_score;
+                Some(r)
+            })
+            .collect()
+    }
+
     /// Reinforce the records a query returned. The new weights are persisted by
     /// the next checkpoint (any write that flushes, `flush_wal`, or drop) — not
     /// by rewriting the whole store inside the query, which is what made

crates/clawhdf5-agent/src/session.rs

@@ -33,7 +33,7 @@ impl SessionCache {
         self.entries.is_empty()
     }
 
-    /// Add a new session with its summary.
+    /// Add a new session with its summary, timestamped now.
     pub fn add(
         &mut self,
         id: &str,
@@ -47,6 +47,21 @@ impl SessionCache {
             .unwrap_or_default()
             .as_secs_f64()
             * 1_000_000.0; // microseconds
+        self.add_at(id, start_idx, end_idx, channel, summary, ts);
+    }
+
+    /// Add a session with an explicit timestamp (Unix **microseconds**, the
+    /// unit [`SessionEntry::ts`] uses) — for importers carrying sessions over
+    /// from another store, whose original time should be kept.
+    pub fn add_at(
+        &mut self,
+        id: &str,
+        start_idx: usize,
+        end_idx: usize,
+        channel: &str,
+        summary: &str,
+        ts: f64,
+    ) {
         self.entries.push(SessionEntry {
             id: id.to_string(),
             start_idx: start_idx as u64,

crates/clawhdf5-agent/src/signing.rs

@@ -0,0 +1,419 @@
+//! Ed25519-signed checkpoints.
+//!
+//! When a signing key is set ([`crate::HDF5Memory::set_signing_key`]), every
+//! checkpoint writes a signed manifest of the store: a SHA-256 per memory
+//! record rolled into a Merkle root, plus hashes of the store's settings, its
+//! sessions and its knowledge graph. [`verify_store`] recomputes all of it from
+//! the file and checks the signature against a public key the caller trusts,
+//! so any change to the checkpointed file — a record's text or embedding, a
+//! setting, a session, a graph edge, made through this crate or any other HDF5
+//! tool — is detected, and the per-record hashes say which records changed.
+//!
+//! What it does not cover: saves still only in the WAL (made since the last
+//! checkpoint). [`VerifyReport::wal_entries_unsigned`] counts them.
+//!
+//! The hashes cover exactly what the file persists, in the form the loader
+//! returns it, so a store verifies after any number of reopen/checkpoint
+//! cycles. Derived data (L2 norms, the vector index) is not covered; it is
+//! recomputed from covered data.
+
+use ed25519_dalek::{Signature, Signer, Verifier};
+pub use ed25519_dalek::{SigningKey, VerifyingKey};
+use sha2::{Digest, Sha256};
+
+use crate::MemoryConfig;
+use crate::cache::MemoryCache;
+use crate::knowledge::KnowledgeCache;
+use crate::session::SessionCache;
+use crate::wal::WalMark;
+
+/// Version of the manifest encoding; part of what is signed.
+pub const MANIFEST_VERSION: i64 = 1;
+
+type Hash = [u8; 32];
+
+/// The hashes a signature covers.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Manifest {
+    pub record_count: u64,
+    /// Merkle root over the per-record hashes.
+    pub records_root: Hash,
+    /// Settings persisted in `/meta`, plus the checkpoint's WAL mark.
+    pub settings: Hash,
+    pub sessions: Hash,
+    pub graph: Hash,
+}
+
+impl Manifest {
+    /// The exact bytes that are signed.
+    pub fn signed_bytes(&self) -> Vec<u8> {
+        let mut m = Vec::with_capacity(160);
+        m.extend_from_slice(b"clawhdf5-agent signed checkpoint\0");
+        m.extend_from_slice(&MANIFEST_VERSION.to_le_bytes());
+        m.extend_from_slice(&self.record_count.to_le_bytes());
+        m.extend_from_slice(&self.records_root);
+        m.extend_from_slice(&self.settings);
+        m.extend_from_slice(&self.sessions);
+        m.extend_from_slice(&self.graph);
+        m
+    }
+}
+
+/// A signature as stored in a checkpoint.
+#[derive(Debug, Clone)]
+pub struct StoredSignature {
+    pub manifest: Manifest,
+    pub record_hashes: Vec<Hash>,
+    pub public_key: [u8; 32],
+    pub signature: [u8; 64],
+}
+
+/// Build the manifest (and per-record hashes) for the state about to be
+/// checkpointed, and sign it.
+pub fn sign(
+    key: &SigningKey,
+    config: &MemoryConfig,
+    cache: &MemoryCache,
+    sessions: &SessionCache,
+    knowledge: &KnowledgeCache,
+    wal_applied: Option<WalMark>,
+) -> StoredSignature {
+    let (manifest, record_hashes) = manifest(config, cache, sessions, knowledge, wal_applied);
+    let signature = key.sign(&manifest.signed_bytes()).to_bytes();
+    StoredSignature {
+        manifest,
+        record_hashes,
+        public_key: key.verifying_key().to_bytes(),
+        signature,
+    }
+}
+
+/// Compute the manifest of a store's state.
+pub fn manifest(
+    config: &MemoryConfig,
+    cache: &MemoryCache,
+    sessions: &SessionCache,
+    knowledge: &KnowledgeCache,
+    wal_applied: Option<WalMark>,
+) -> (Manifest, Vec<Hash>) {
+    let record_hashes: Vec<Hash> = (0..cache.len()).map(|i| record_hash(cache, i)).collect();
+    let manifest = Manifest {
+        record_count: cache.len() as u64,
+        records_root: merkle_root(&record_hashes),
+        settings: settings_hash(config, wal_applied),
+        sessions: sessions_hash(sessions),
+        graph: graph_hash(knowledge),
+    };
+    (manifest, record_hashes)
+}
+
+// ---------------------------------------------------------------------------
+// Canonical encoding
+// ---------------------------------------------------------------------------
+
+/// A SHA-256 over length-prefixed fields, so no two different field lists
+/// hash the same bytes.
+struct Fields(Sha256);
+
+impl Fields {
+    fn new(domain: &str) -> Self {
+        let mut h = Sha256::new();
+        h.update((domain.len() as u64).to_le_bytes());
+        h.update(domain.as_bytes());
+        Self(h)
+    }
+    fn bytes(&mut self, b: &[u8]) -> &mut Self {
+        self.0.update((b.len() as u64).to_le_bytes());
+        self.0.update(b);
+        self
+    }
+    /// Strings as the loader returns them: stored null-padded, so a trailing
+    /// NUL cannot survive a round trip and must not be part of the hash.
+    fn str(&mut self, s: &str) -> &mut Self {
+        self.bytes(s.trim_end_matches('\0').as_bytes())
+    }
+    fn u64(&mut self, v: u64) -> &mut Self {
+        self.0.update(v.to_le_bytes());
+        self
+    }
+    fn f64(&mut self, v: f64) -> &mut Self {
+        self.0.update(v.to_bits().to_le_bytes());
+        self
+    }
+    fn f32(&mut self, v: f32) -> &mut Self {
+        self.0.update(v.to_bits().to_le_bytes());
+        self
+    }
+    fn finish(self) -> Hash {
+        self.0.finalize().into()
+    }
+}
+
+/// Everything persisted about record `i`, including its position. The
+/// embedding is hashed as the cache holds it — for a `float16` store that is
+/// the half-rounded value the file holds.
+fn record_hash(cache: &MemoryCache, i: usize) -> Hash {
+    let mut f = Fields::new("clawhdf5-agent/record");
+    f.u64(i as u64).str(&cache.chunks[i]);
+    let emb: Vec<u8> = cache.embeddings[i]
+        .iter()
+        .flat_map(|v| v.to_bits().to_le_bytes())
+        .collect();
+    f.bytes(&emb)
+        .str(&cache.source_channels[i])
+        .f64(cache.timestamps[i])
+        .str(&cache.session_ids[i])
+        .str(&cache.tags[i])
+        .u64(u64::from(cache.tombstones[i]))
+        .f32(cache.activation_weights[i]);
+    f.finish()
+}
+
+/// Binary Merkle tree: leaves are the record hashes; a parent hashes its two
+/// children with a node prefix; an odd node is carried up unchanged.
+fn merkle_root(leaves: &[Hash]) -> Hash {
+    if leaves.is_empty() {
+        return Fields::new("clawhdf5-agent/merkle-empty").finish();
+    }
+    let mut level: Vec<Hash> = leaves.to_vec();
+    while level.len() > 1 {
+        level = level
+            .chunks(2)
+            .map(|pair| match pair {
+                [l, r] => {
+                    let mut h = Sha256::new();
+                    h.update([1u8]);
+                    h.update(l);
+                    h.update(r);
+                    h.finalize().into()
+                }
+                [only] => *only,
+                _ => unreachable!(),
+            })
+            .collect();
+    }
+    level[0]
+}
+
+fn settings_hash(c: &MemoryConfig, wal_applied: Option<WalMark>) -> Hash {
+    let mut f = Fields::new("clawhdf5-agent/settings");
+    f.str(crate::schema::SCHEMA_VERSION)
+        .str(&c.created_at)
+        .str(&c.agent_id)
+        .str(&c.embedder)
+        .u64(c.embedding_dim as u64)
+        .u64(c.chunk_size as u64)
+        .u64(c.overlap as u64)
+        .u64(u64::from(c.float16))
+        .u64(u64::from(c.compression))
+        .u64(u64::from(c.compression_level))
+        .f32(c.compact_threshold)
+        .f32(c.hebbian_boost)
+        .f32(c.decay_factor)
+        .u64(u64::from(c.wal_enabled))
+        .u64(c.wal_max_entries as u64)
+        .u64(u64::from(c.quantized_index))
+        .u64(c.hnsw_m as u64)
+        .u64(c.hnsw_ef_construction as u64)
+        .u64(c.hnsw_ef_search as u64);
+    // An empty mark is not written to the file, so it must hash as none.
+    match wal_applied.filter(|m| m.len > 0) {
+        Some(m) => f.u64(1).u64(m.len).u64(u64::from(m.crc)),
+        None => f.u64(0),
+    };
+    f.finish()
+}
+
+fn sessions_hash(s: &SessionCache) -> Hash {
+    let mut f = Fields::new("clawhdf5-agent/sessions");
+    f.u64(s.entries.len() as u64);
+    for (i, e) in s.entries.iter().enumerate() {
+        f.str(&e.id)
+            .u64(e.start_idx)
+            .u64(e.end_idx)
+            .str(&e.channel)
+            .f64(e.ts)
+            .str(s.summaries.get(i).map(String::as_str).unwrap_or(""));
+    }
+    f.finish()
+}
+
+fn graph_hash(k: &KnowledgeCache) -> Hash {
+    let mut f = Fields::new("clawhdf5-agent/graph");
+    f.u64(k.entities.len() as u64);
+    for e in &k.entities {
+        f.u64(e.id)
+            .str(&e.name)
+            .str(&e.entity_type)
+            .u64(e.embedding_idx as u64);
+    }
+    f.u64(k.relations.len() as u64);
+    for r in &k.relations {
+        f.u64(r.src)
+            .u64(r.tgt)
+            .str(&r.relation)
+            .f32(r.weight)
+            .f64(r.ts);
+    }
+    f.u64(k.alias_strings.len() as u64);
+    for (s, id) in k.alias_strings.iter().zip(&k.alias_entity_ids) {
+        f.str(s).u64(*id as u64);
+    }
+    f.finish()
+}
+
+// ---------------------------------------------------------------------------
+// Verification
+// ---------------------------------------------------------------------------
+
+/// The outcome of [`verify_store`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct VerifyReport {
+    /// The checkpoint carries a signature.
+    pub signed: bool,
+    /// The signature was made by the key the caller trusts.
+    pub key_matches: bool,
+    /// The signature over the stored manifest is valid.
+    pub signature_valid: bool,
+    /// The file's current contents match the signed manifest.
+    pub records_match: bool,
+    pub settings_match: bool,
+    pub sessions_match: bool,
+    pub graph_match: bool,
+    /// Records whose contents differ from what was signed (by position),
+    /// when the stored per-record hashes are themselves authentic.
+    pub changed_records: Vec<usize>,
+    /// Records in the file versus in the signed manifest.
+    pub record_count: u64,
+    pub signed_record_count: u64,
+    /// The public key the checkpoint claims to be signed by.
+    pub public_key: Option<[u8; 32]>,
+    /// Saves in the WAL after the checkpoint: not covered by the signature.
+    pub wal_entries_unsigned: usize,
+}
+
+impl VerifyReport {
+    /// Signed by the trusted key, signature valid, and every part of the
+    /// file unchanged since it was signed.
+    pub fn is_valid(&self) -> bool {
+        self.signed
+            && self.key_matches
+            && self.signature_valid
+            && self.records_match
+            && self.settings_match
+            && self.sessions_match
+            && self.graph_match
+    }
+}
+
+/// Check a store file against the public key the caller trusts.
+///
+/// Reads the checkpoint (not the WAL), recomputes every hash from its
+/// contents and checks the signature. Never writes.
+pub fn verify_store(
+    path: &std::path::Path,
+    trusted: &VerifyingKey,
+) -> Result<VerifyReport, crate::MemoryError> {
+    let file = clawhdf5::File::open(path)
+        .map_err(|e| crate::MemoryError::Hdf5(format!("cannot open {}: {e}", path.display())))?;
+    let (config, cache, sessions, knowledge) = crate::schema::validate_and_load(&file)?;
+    let checkpoint = crate::schema::read_checkpoint_meta(&file);
+    let stored = crate::schema::read_signature(&file)?;
+    let wal_entries_unsigned = count_wal_entries_after(path, checkpoint.wal_applied);
+
+    let (current, current_hashes) = manifest(
+        &config,
+        &cache,
+        &sessions,
+        &knowledge,
+        checkpoint.wal_applied,
+    );
+
+    let Some(stored) = stored else {
+        return Ok(VerifyReport {
+            signed: false,
+            key_matches: false,
+            signature_valid: false,
+            records_match: false,
+            settings_match: false,
+            sessions_match: false,
+            graph_match: false,
+            changed_records: Vec::new(),
+            record_count: current.record_count,
+            signed_record_count: 0,
+            public_key: None,
+            wal_entries_unsigned,
+        });
+    };
+
+    let key_matches = stored.public_key == trusted.to_bytes();
+    let signature_valid = trusted
+        .verify(
+            &stored.manifest.signed_bytes(),
+            &Signature::from_bytes(&stored.signature),
+        )
+        .is_ok();
+    // The stored per-record hashes can localise a change only if they are
+    // the ones that were signed.
+    let hashes_authentic = signature_valid
+        && stored.record_hashes.len() as u64 == stored.manifest.record_count
+        && merkle_root(&stored.record_hashes) == stored.manifest.records_root;
+    let changed_records = if hashes_authentic {
+        let n = current_hashes.len().max(stored.record_hashes.len());
+        (0..n)
+            .filter(|&i| current_hashes.get(i) != stored.record_hashes.get(i))
+            .collect()
+    } else {
+        Vec::new()
+    };
+
+    Ok(VerifyReport {
+        signed: true,
+        key_matches,
+        signature_valid,
+        records_match: signature_valid
+            && current.record_count == stored.manifest.record_count
+            && current.records_root == stored.manifest.records_root,
+        settings_match: signature_valid && current.settings == stored.manifest.settings,
+        sessions_match: signature_valid && current.sessions == stored.manifest.sessions,
+        graph_match: signature_valid && current.graph == stored.manifest.graph,
+        changed_records,
+        record_count: current.record_count,
+        signed_record_count: stored.manifest.record_count,
+        public_key: Some(stored.public_key),
+        wal_entries_unsigned,
+    })
+}
+
+fn count_wal_entries_after(store: &std::path::Path, mark: Option<WalMark>) -> usize {
+    let wal = store.with_extension("h5.wal");
+    if !wal.exists() {
+        return 0;
+    }
+    crate::wal::WalFile::read_entries_for_migration(&wal, mark)
+        .map(|e| e.len())
+        .unwrap_or(0)
+}
+
+/// A new random signing key from the operating system's RNG.
+pub fn generate_key() -> SigningKey {
+    SigningKey::generate(&mut rand_core::OsRng)
+}
+
+/// Hex encoding for keys and signatures in attributes and the CLI.
+pub fn to_hex(bytes: &[u8]) -> String {
+    bytes.iter().map(|b| format!("{b:02x}")).collect()
+}
+
+/// Parse hex into exactly `N` bytes.
+pub fn from_hex<const N: usize>(s: &str) -> Option<[u8; N]> {
+    let s = s.trim();
+    if s.len() != 2 * N {
+        return None;
+    }
+    let mut out = [0u8; N];
+    for (i, byte) in out.iter_mut().enumerate() {
+        *byte = u8::from_str_radix(&s[2 * i..2 * i + 2], 16).ok()?;
+    }
+    Some(out)
+}

crates/clawhdf5-agent/src/storage.rs

@@ -36,7 +36,7 @@ pub fn write_to_disk_with_mark(
 ) -> Result<(), MemoryError> {
     let meta = schema::CheckpointMeta {
         wal_applied,
-        ann_generation: None,
+        ..schema::CheckpointMeta::default()
     };
     write_to_disk_with_meta(path, config, cache, sessions, knowledge, &meta)
 }
@@ -50,7 +50,21 @@ pub fn write_to_disk_with_meta(
     knowledge: &KnowledgeCache,
     checkpoint: &schema::CheckpointMeta,
 ) -> Result<(), MemoryError> {
-    let bytes = schema::build_hdf5_file_with_meta(config, cache, sessions, knowledge, checkpoint)?;
+    write_to_disk_signed(path, config, cache, sessions, knowledge, checkpoint, None)
+}
+
+/// [`write_to_disk_with_meta`] with a signed manifest of the contents.
+pub fn write_to_disk_signed(
+    path: &Path,
+    config: &MemoryConfig,
+    cache: &MemoryCache,
+    sessions: &SessionCache,
+    knowledge: &KnowledgeCache,
+    checkpoint: &schema::CheckpointMeta,
+    signature: Option<&crate::signing::StoredSignature>,
+) -> Result<(), MemoryError> {
+    let bytes =
+        schema::build_hdf5_file_signed(config, cache, sessions, knowledge, checkpoint, signature)?;
 
     if bytes.is_empty() {
         return Err(MemoryError::Hdf5("build_hdf5_file produced 0 bytes".into()));
@@ -113,13 +127,11 @@ pub type StoreState = (MemoryConfig, MemoryCache, SessionCache, KnowledgeCache);
 /// [`read_from_disk`], plus the checkpoint's [`WalMark`] (if any) so the
 /// caller can skip WAL entries this file already contains.
 pub fn read_from_disk_with_mark(path: &Path) -> Result<(StoreState, Option<WalMark>), MemoryError> {
-    let mmap = clawhdf5_io::MmapReader::open(path).map_err(MemoryError::Io)?;
-
-    // Advise the OS we'll need the whole file for parsing
-    mmap.advise_willneed(0, mmap.len());
-
-    // Parse the HDF5 file from the mmap'd bytes
-    let file = clawhdf5::File::from_bytes(mmap.as_bytes().to_vec())
+    // `File::open` memory-maps the file itself (the facade's `mmap` feature is
+    // on by default). Mapping it here and handing over `as_bytes().to_vec()`
+    // did the same work and then copied the whole store — a second full copy
+    // of the file, live for the whole parse, on top of the mapping.
+    let file = clawhdf5::File::open(path)
         .map_err(|e| MemoryError::Hdf5(format!("cannot open {}: {e}", path.display())))?;
 
     let (mut config, cache, sessions, knowledge) = schema::validate_and_load(&file)?;
@@ -133,9 +145,7 @@ pub fn read_from_disk_with_mark(path: &Path) -> Result<(StoreState, Option<WalMa
 pub fn read_from_disk_with_meta(
     path: &Path,
 ) -> Result<(StoreState, schema::CheckpointMeta), MemoryError> {
-    let mmap = clawhdf5_io::MmapReader::open(path).map_err(MemoryError::Io)?;
-    mmap.advise_willneed(0, mmap.len());
-    let file = clawhdf5::File::from_bytes(mmap.as_bytes().to_vec())
+    let file = clawhdf5::File::open(path)
         .map_err(|e| MemoryError::Hdf5(format!("cannot open {}: {e}", path.display())))?;
     let (mut config, cache, sessions, knowledge) = schema::validate_and_load(&file)?;
     config.path = path.to_path_buf();

crates/clawhdf5-agent/tests/float16_store.rs

@@ -0,0 +1,300 @@
+//! `MemoryConfig::float16`: embeddings stored as IEEE half precision.
+//!
+//! The setting used to be recorded in `/meta` and otherwise ignored — the
+//! embeddings dataset was always `f32`. These tests pin what it now does: the
+//! dataset is `float16`, the in-memory cache holds exactly the values the file
+//! holds (so search results survive a reopen bit for bit), and a value half
+//! precision cannot represent is refused rather than stored as infinity.
+
+use std::path::{Path, PathBuf};
+
+use clawhdf5_agent::{AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry, MemoryError};
+use clawhdf5_format::float16::round_to_f16;
+use tempfile::TempDir;
+
+const DIM: usize = 64;
+
+/// Deterministic, embedding-like unit vectors.
+fn embedding(seed: u64) -> Vec<f32> {
+    let mut x = seed.wrapping_mul(0x9E37_79B9_7F4A_7C15) | 1;
+    let v: Vec<f32> = (0..DIM)
+        .map(|_| {
+            x ^= x << 13;
+            x ^= x >> 7;
+            x ^= x << 17;
+            (x >> 40) as f32 / (1u64 << 24) as f32 - 0.5
+        })
+        .collect();
+    let norm = v.iter().map(|a| a * a).sum::<f32>().sqrt();
+    v.iter().map(|a| a / norm).collect()
+}
+
+fn entry(i: u64) -> MemoryEntry {
+    MemoryEntry {
+        chunk: format!("memory number {i} about topic {}", i % 7),
+        embedding: embedding(i),
+        source_channel: "test".into(),
+        timestamp: i as f64,
+        session_id: "s".into(),
+        tags: format!("t{i}"),
+    }
+}
+
+fn config(dir: &TempDir, name: &str, float16: bool) -> MemoryConfig {
+    let mut c = MemoryConfig::new(dir.path().join(name), "agent", DIM);
+    c.float16 = float16;
+    c
+}
+
+fn embeddings_dtype_and_values(path: &Path) -> (String, Vec<f32>) {
+    let file = clawhdf5::File::open(path).unwrap();
+    let ds = file.dataset("memory/embeddings").unwrap();
+    (format!("{:?}", ds.dtype().unwrap()), ds.read_f32().unwrap())
+}
+
+fn search_bits(m: &mut HDF5Memory, q: u64) -> Vec<(usize, u32)> {
+    m.hybrid_search(&embedding(q), "memory topic 3", 0.4, 0.6, 10)
+        .iter()
+        .map(|r| (r.index, r.score.to_bits()))
+        .collect()
+}
+
+#[test]
+fn float16_store_writes_half_precision_and_reopens_identically() {
+    let dir = TempDir::new().unwrap();
+    // Two identical stores. Search is not read-only (it boosts the Hebbian
+    // activation of what it returns, and checkpoints persist that), so each
+    // is queried exactly once: one live, one after a checkpoint and reopen.
+    let live_cfg = config(&dir, "live.h5", true);
+    let cfg = config(&dir, "f16.h5", true);
+    let path: PathBuf = cfg.path.clone();
+
+    let mut live = HDF5Memory::create(live_cfg).unwrap();
+    live.save_batch((0..200).map(entry).collect()).unwrap();
+    let mut m = HDF5Memory::create(cfg).unwrap();
+    m.save_batch((0..200).map(entry).collect()).unwrap();
+    drop(m);
+
+    // On disk: a genuine float16 dataset holding the rounded inputs.
+    let (dtype, values) = embeddings_dtype_and_values(&path);
+    assert_eq!(dtype, "Other(\"float16\")");
+    let expected: Vec<u32> = (0..200)
+        .flat_map(|i| embedding(i).into_iter().map(|v| round_to_f16(v).to_bits()))
+        .collect();
+    let got: Vec<u32> = values.iter().map(|v| v.to_bits()).collect();
+    assert_eq!(got, expected);
+
+    // Reopened, the store answers exactly as the live one does: the cache
+    // held the half-rounded values before the checkpoint.
+    let mut reopened = HDF5Memory::open(&path).unwrap();
+    for q in 0..5 {
+        assert_eq!(
+            search_bits(&mut live, 1000 + q),
+            search_bits(&mut reopened, 1000 + q),
+            "query {q}"
+        );
+    }
+}
+
+#[test]
+fn float16_halves_the_embeddings_on_disk() {
+    let dir = TempDir::new().unwrap();
+    let mut sizes = Vec::new();
+    for float16 in [false, true] {
+        let cfg = config(&dir, &format!("s{float16}.h5"), float16);
+        let path = cfg.path.clone();
+        let mut m = HDF5Memory::create(cfg).unwrap();
+        m.save_batch((0..2000).map(entry).collect()).unwrap();
+        drop(m);
+        sizes.push(std::fs::metadata(&path).unwrap().len());
+    }
+    let embedding_bytes_f32 = (2000 * DIM * 4) as u64;
+    let saved = sizes[0] - sizes[1];
+    // Half of the f32 embeddings, give or take metadata and alignment.
+    assert!(
+        saved.abs_diff(embedding_bytes_f32 / 2) < 16 * 1024,
+        "f32 {} B, f16 {} B, saved {saved} B, expected ~{} B",
+        sizes[0],
+        sizes[1],
+        embedding_bytes_f32 / 2
+    );
+}
+
+#[test]
+fn f32_store_is_unchanged() {
+    let dir = TempDir::new().unwrap();
+    let cfg = config(&dir, "f32.h5", false);
+    let path = cfg.path.clone();
+    let mut m = HDF5Memory::create(cfg).unwrap();
+    m.save_batch((0..50).map(entry).collect()).unwrap();
+    drop(m);
+    let (dtype, values) = embeddings_dtype_and_values(&path);
+    assert_eq!(dtype, "F32");
+    let expected: Vec<f32> = (0..50).flat_map(embedding).collect();
+    assert_eq!(values, expected);
+}
+
+#[test]
+fn out_of_range_values_are_refused_not_stored_as_infinity() {
+    let dir = TempDir::new().unwrap();
+    let mut cfg = config(&dir, "range.h5", true);
+    cfg.wal_enabled = true;
+    let path = cfg.path.clone();
+    let mut m = HDF5Memory::create(cfg).unwrap();
+    m.save(entry(1)).unwrap();
+
+    let mut bad = entry(2);
+    bad.embedding[5] = 70_000.0;
+    match m.save(bad.clone()) {
+        Err(MemoryError::InvalidEntry(msg)) => assert!(msg.contains("embedding[5]"), "{msg}"),
+        other => panic!("expected InvalidEntry, got {other:?}"),
+    }
+    assert!(matches!(
+        m.save_or_update(bad.clone()),
+        Err(MemoryError::InvalidEntry(_))
+    ));
+    // A batch is all or nothing.
+    assert!(matches!(
+        m.save_batch(vec![entry(3), bad.clone(), entry(4)]),
+        Err(MemoryError::InvalidEntry(_))
+    ));
+    assert_eq!(m.count(), 1);
+
+    // The largest finite half, and values that round down to it, are fine.
+    let mut edge = entry(5);
+    edge.embedding[0] = 65504.0;
+    edge.embedding[1] = -65519.0;
+    m.save(edge).unwrap();
+    assert_eq!(m.count(), 2);
+    drop(m);
+
+    // Nothing rejected reached the WAL or the file.
+    let m = HDF5Memory::open(&path).unwrap();
+    assert_eq!(m.count(), 2);
+
+    // An f32 store takes the same value as it always did.
+    let mut m32 = HDF5Memory::create(config(&dir, "range32.h5", false)).unwrap();
+    m32.save(bad).unwrap();
+}
+
+#[test]
+fn wal_replay_rounds_like_a_live_save() {
+    let dir = TempDir::new().unwrap();
+    let mut cfg = config(&dir, "wal.h5", true);
+    cfg.wal_enabled = true;
+    cfg.wal_max_entries = 10_000; // keep everything in the WAL
+    let path = cfg.path.clone();
+    let mut m = HDF5Memory::create(cfg).unwrap();
+    for i in 0..30 {
+        m.save(entry(i)).unwrap();
+    }
+    let live = search_bits(&mut m, 77);
+
+    // Crash image: the .h5 is still the empty checkpoint; everything is in
+    // the WAL, which holds the caller's f32 values.
+    let crash = TempDir::new().unwrap();
+    let image = crash.path().join("image.h5");
+    std::fs::copy(&path, &image).unwrap();
+    std::fs::copy(
+        path.with_extension("h5.wal"),
+        image.with_extension("h5.wal"),
+    )
+    .unwrap();
+    drop(m);
+
+    let mut recovered = HDF5Memory::open(&image).unwrap();
+    assert_eq!(recovered.count(), 30);
+    assert_eq!(search_bits(&mut recovered, 77), live);
+}
+
+#[test]
+fn new_stores_default_to_float16() {
+    let dir = TempDir::new().unwrap();
+    let path = dir.path().join("default.h5");
+    let mut m = HDF5Memory::create(MemoryConfig::new(path.clone(), "agent", DIM)).unwrap();
+    assert!(m.config().float16);
+    m.save_batch((0..10).map(entry).collect()).unwrap();
+    drop(m);
+    assert_eq!(embeddings_dtype_and_values(&path).0, "Other(\"float16\")");
+    assert!(HDF5Memory::open(&path).unwrap().config().float16);
+}
+
+#[test]
+fn an_existing_f32_store_stays_f32() {
+    // Written by the v2.5.0 CLI, with `float16 = 0` in /meta (every agent
+    // store has recorded it). Flipping the default for new stores must not
+    // reach back and round an existing store's embeddings.
+    let dir = TempDir::new().unwrap();
+    let path = dir.path().join("legacy.h5");
+    std::fs::copy(
+        concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/tests/fixtures/store_v2_5_0.h5"
+        ),
+        &path,
+    )
+    .unwrap();
+    let before = embeddings_dtype_and_values(&path);
+    assert_eq!(before.0, "F32");
+
+    let mut m = HDF5Memory::open(&path).unwrap();
+    assert!(!m.config().float16, "an old store must reopen as f32");
+    let dim = m.config().embedding_dim;
+    let odd: Vec<f32> = (0..dim).map(|i| 0.1 + i as f32 * 1e-4).collect();
+    m.save_batch(vec![MemoryEntry {
+        chunk: "added after the upgrade".into(),
+        embedding: odd.clone(),
+        source_channel: "test".into(),
+        timestamp: 1.0,
+        session_id: "s".into(),
+        tags: String::new(),
+    }])
+    .unwrap();
+    drop(m);
+
+    // Checkpointed: still f32, the old rows untouched and the new one exact.
+    let (dtype, values) = embeddings_dtype_and_values(&path);
+    assert_eq!(dtype, "F32");
+    assert_eq!(&values[..before.1.len()], before.1.as_slice());
+    assert_eq!(&values[before.1.len()..], odd.as_slice());
+}
+
+/// `Group::attrs` leaves out an attribute it cannot decode. A store whose
+/// `float16` setting is unreadable must not open as `float16 = false` (or with
+/// any other default in place of a setting it has): it is an error.
+#[test]
+fn unreadable_meta_attribute_fails_open_instead_of_defaulting() {
+    let dir = TempDir::new().unwrap();
+    let path = dir.path().join("store.h5");
+    {
+        let mut m = HDF5Memory::create(config(&dir, "store.h5", true)).unwrap();
+        m.save(entry(1)).unwrap();
+        m.flush_wal().unwrap();
+    }
+    assert!(HDF5Memory::open_read_only(&path).is_ok());
+
+    // Give the `float16` attribute message an unknown version (the name is
+    // at +8 in a version-1 message and +9 in a version-3 one).
+    let mut bytes = std::fs::read(&path).unwrap();
+    let name = b"float16\0";
+    let mut hit = false;
+    let positions: Vec<usize> = (9..bytes.len() - name.len())
+        .filter(|&p| &bytes[p..p + name.len()] == name)
+        .collect();
+    for pos in positions {
+        for (back, version) in [(8, 1u8), (9, 3u8)] {
+            if bytes[pos - back] == version {
+                bytes[pos - back] = 0x7f;
+                hit = true;
+            }
+        }
+    }
+    assert!(hit, "float16 attribute message not found");
+    std::fs::write(&path, &bytes).unwrap();
+
+    match HDF5Memory::open_read_only(&path) {
+        Err(MemoryError::Schema(msg)) => assert!(msg.contains("/meta"), "{msg}"),
+        Err(e) => panic!("unexpected error: {e}"),
+        Ok(_) => panic!("store opened with an unreadable float16 setting"),
+    }
+}

crates/clawhdf5-agent/tests/h5py_interop.rs

@@ -0,0 +1,155 @@
+//! An agent store is a standard HDF5 file: h5py can open it and read every
+//! dataset.
+//!
+//! It could not: the float datatype's sign-bit position was hard-coded for
+//! f64, so every f32 dataset (embeddings, norms, activation weights) made
+//! libhdf5 refuse the file with "sign bit position out of bounds".
+
+use std::process::Command;
+
+use clawhdf5_agent::{AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry};
+
+fn python() -> String {
+    std::env::var("CLAWHDF5_PYTHON").unwrap_or_else(|_| "python3".to_string())
+}
+
+fn h5py_available() -> bool {
+    Command::new(python())
+        .args(["-c", "import h5py"])
+        .output()
+        .map(|o| o.status.success())
+        .unwrap_or(false)
+}
+
+#[test]
+fn h5py_reads_every_dataset_of_an_agent_store() {
+    if !h5py_available() {
+        assert!(
+            std::env::var("CLAWHDF5_REQUIRE_INTEROP").as_deref() != Ok("1"),
+            "CLAWHDF5_REQUIRE_INTEROP=1 but python3 with h5py is not available"
+        );
+        eprintln!("SKIP: python3 with h5py not available");
+        return;
+    }
+    let dir = tempfile::tempdir().unwrap();
+    for float16 in [false, true] {
+        let path = dir.path().join(format!("store_{float16}.h5"));
+        let mut cfg = MemoryConfig::new(path.clone(), "agent", 8);
+        cfg.float16 = float16;
+        let mut m = HDF5Memory::create(cfg).unwrap();
+        // save_batch checkpoints, so the records are in the .h5, not the WAL.
+        m.save_batch(
+            (0..20)
+                .map(|i| MemoryEntry {
+                    chunk: format!("memory {i}"),
+                    embedding: (0..8).map(|j| ((i * 8 + j) as f32).sin()).collect(),
+                    source_channel: "test".into(),
+                    timestamp: i as f64,
+                    session_id: "s".into(),
+                    tags: String::new(),
+                })
+                .collect(),
+        )
+        .unwrap();
+        drop(m);
+
+        // Exact expected values, as bits: numpy's sin need not match Rust's
+        // to the last place.
+        let bits = (0..160)
+            .map(|k| (k as f32).sin().to_bits().to_string())
+            .collect::<Vec<_>>()
+            .join(",");
+        let script = format!(
+            r#"
+import h5py, numpy as np
+want = np.float16 if {py_bool} else np.float32
+with h5py.File("{path}", "r") as f:
+    names = []
+    f.visititems(lambda n, o: names.append(n) if isinstance(o, h5py.Dataset) else None)
+    for n in names:
+        f[n][()]  # every dataset must decode
+    e = f["memory/embeddings"]
+    assert e.dtype == want, e.dtype
+    assert e.shape == (20, 8), e.shape
+    ref = np.array([{bits}], dtype=np.uint32).view(np.float32).astype(want).reshape(20, 8)
+    assert (e[()] == ref).all()
+    assert f["memory/norms"].dtype == np.float32
+print(len(names))
+"#,
+            py_bool = if float16 { "True" } else { "False" },
+            path = path.display()
+        );
+        let out = Command::new(python())
+            .args(["-c", &script])
+            .output()
+            .unwrap();
+        assert!(
+            out.status.success(),
+            "float16={float16}: {}",
+            String::from_utf8_lossy(&out.stderr)
+        );
+        let n: usize = String::from_utf8_lossy(&out.stdout).trim().parse().unwrap();
+        assert!(n >= 10, "only {n} datasets");
+    }
+}
+
+#[test]
+fn an_edit_made_with_h5py_breaks_the_signature_and_names_the_record() {
+    if !h5py_available() {
+        assert!(
+            std::env::var("CLAWHDF5_REQUIRE_INTEROP").as_deref() != Ok("1"),
+            "CLAWHDF5_REQUIRE_INTEROP=1 but python3 with h5py is not available"
+        );
+        eprintln!("SKIP: python3 with h5py not available");
+        return;
+    }
+    use clawhdf5_agent::signing::SigningKey;
+    let dir = tempfile::tempdir().unwrap();
+    let path = dir.path().join("signed.h5");
+    let key = SigningKey::from_bytes(&[42; 32]);
+    let mut m = HDF5Memory::create(MemoryConfig::new(path.clone(), "agent", 8)).unwrap();
+    m.set_signing_key(key.clone());
+    m.save_batch(
+        (0..10)
+            .map(|i| MemoryEntry {
+                chunk: format!("memory {i}"),
+                embedding: (0..8).map(|j| ((i * 8 + j) as f32).cos()).collect(),
+                source_channel: "test".into(),
+                timestamp: i as f64,
+                session_id: "s".into(),
+                tags: String::new(),
+            })
+            .collect(),
+    )
+    .unwrap();
+    drop(m);
+    assert!(
+        HDF5Memory::verify(&path, &key.verifying_key())
+            .unwrap()
+            .is_valid()
+    );
+
+    // Someone edits one timestamp in place with h5py.
+    let script = format!(
+        r#"
+import h5py
+with h5py.File("{}", "r+") as f:
+    ts = f["memory/timestamps"]
+    ts[3] = 12345.0
+"#,
+        path.display()
+    );
+    let out = Command::new(python())
+        .args(["-c", &script])
+        .output()
+        .unwrap();
+    assert!(
+        out.status.success(),
+        "{}",
+        String::from_utf8_lossy(&out.stderr)
+    );
+
+    let r = HDF5Memory::verify(&path, &key.verifying_key()).unwrap();
+    assert!(r.signature_valid && !r.is_valid(), "{r:?}");
+    assert_eq!(r.changed_records, vec![3]);
+}

crates/clawhdf5-agent/tests/hnsw_integration.rs

@@ -234,3 +234,113 @@ fn quantized_index_setting_survives_a_reopen() {
     let reopened = HDF5Memory::open(&path).unwrap();
     assert!(reopened.config().quantized_index);
 }
+
+#[test]
+fn hnsw_parameters_are_configurable_and_persisted() {
+    // The graph degree and both candidate-list sizes used to be constants, so
+    // a deployment could not trade recall against memory or speed at all.
+    let dir = TempDir::new().unwrap();
+    let path = dir.path().join("mem.h5");
+    let mut config = MemoryConfig::new(path.clone(), "agent", 16);
+    config.hnsw_m = 8;
+    config.hnsw_ef_construction = 32;
+    config.hnsw_ef_search = 128;
+    let mut mem = HDF5Memory::create(config).unwrap();
+
+    let mut seed = 99;
+    let vectors: Vec<Vec<f32>> = (0..300).map(|_| make_vector(&mut seed, 16)).collect();
+    for (i, v) in vectors.iter().enumerate() {
+        mem.save(entry(&format!("c{i}"), v.clone(), "t")).unwrap();
+    }
+    // Still correct with a smaller graph: an exact match must rank first.
+    let top = mem.hybrid_search(&vectors[42], "", 1.0, 0.0, 1);
+    assert_eq!(top[0].index, 42);
+
+    mem.flush_wal().unwrap();
+    drop(mem);
+    let reopened = HDF5Memory::open(&path).unwrap();
+    assert_eq!(reopened.config().hnsw_m, 8);
+    assert_eq!(reopened.config().hnsw_ef_construction, 32);
+    assert_eq!(reopened.config().hnsw_ef_search, 128);
+}
+
+#[test]
+fn degenerate_hnsw_parameters_do_not_panic() {
+    // `clawhdf5-ann` asserts m >= 2, so a zero from a config file — or from a
+    // caller who assumed 0 meant "default" — would abort the process inside
+    // the index builder. The store clamps instead.
+    let dir = TempDir::new().unwrap();
+    let mut config = MemoryConfig::new(dir.path().join("mem.h5"), "agent", 8);
+    config.hnsw_m = 0;
+    config.hnsw_ef_construction = 0;
+    config.hnsw_ef_search = 1;
+    let mut mem = HDF5Memory::create(config).unwrap();
+
+    let mut seed = 5;
+    let vectors: Vec<Vec<f32>> = (0..50).map(|_| make_vector(&mut seed, 8)).collect();
+    for (i, v) in vectors.iter().enumerate() {
+        mem.save(entry(&format!("c{i}"), v.clone(), "t")).unwrap();
+    }
+    let results = mem.hybrid_search(&vectors[7], "", 1.0, 0.0, 5);
+    assert_eq!(results[0].index, 7, "exact match should still rank first");
+}
+
+#[test]
+fn new_stores_default_to_the_quantized_index() {
+    // int8 is the default because it is smaller and, with an exact re-score,
+    // faster at equal recall on every platform measured (see BENCHMARKS.md).
+    let dir = TempDir::new().unwrap();
+    let config = MemoryConfig::new(dir.path().join("mem.h5"), "agent", 8);
+    assert!(config.quantized_index);
+
+    let path = config.path.clone();
+    let mut mem = HDF5Memory::create(config).unwrap();
+    let mut seed = 3;
+    let vectors: Vec<Vec<f32>> = (0..40).map(|_| make_vector(&mut seed, 8)).collect();
+    for (i, v) in vectors.iter().enumerate() {
+        mem.save(entry(&format!("c{i}"), v.clone(), "t")).unwrap();
+    }
+    assert_eq!(
+        mem.hybrid_search(&vectors[11], "", 1.0, 0.0, 1)[0].index,
+        11
+    );
+    mem.flush_wal().unwrap();
+    drop(mem);
+    assert!(HDF5Memory::open(&path).unwrap().config().quantized_index);
+}
+
+#[test]
+fn a_store_written_before_the_setting_existed_stays_f32() {
+    // `store_v2_5_0.h5` was written by the v2.5.0 CLI, before
+    // `quantized_index` or the HNSW parameters were persisted, so it carries
+    // none of them. Flipping the default for new stores must not reach back
+    // and change how an existing store's index is held.
+    let dir = TempDir::new().unwrap();
+    let path = dir.path().join("legacy.h5");
+    std::fs::copy(
+        concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/tests/fixtures/store_v2_5_0.h5"
+        ),
+        &path,
+    )
+    .unwrap();
+
+    let bytes = std::fs::read(&path).unwrap();
+    assert!(
+        !bytes.windows(15).any(|w| w == b"quantized_index"),
+        "the fixture must predate the setting, or it tests nothing"
+    );
+
+    let mut mem = HDF5Memory::open(&path).unwrap();
+    assert!(
+        !mem.config().quantized_index,
+        "an old store must reopen with an f32 index"
+    );
+    assert_eq!(mem.config().hnsw_m, 16);
+    assert_eq!(mem.config().hnsw_ef_construction, 64);
+    assert_eq!(mem.count(), 6);
+    // And it still searches: entry 3's own embedding finds it first.
+    let hit = mem.hybrid_search(&[3.0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], "", 1.0, 0.0, 1);
+    assert_eq!(hit[0].index, 3);
+}

crates/clawhdf5-agent/tests/search_options.rs

@@ -0,0 +1,344 @@
+//! `HDF5Memory::search` with `SearchOptions`: source filtering, re-ranking and
+//! confidence rejection in the store's own search path.
+
+use std::collections::HashSet;
+
+use clawhdf5_agent::confidence::ConfidenceConfig;
+use clawhdf5_agent::reranker::ReRankConfig;
+use clawhdf5_agent::{AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry, SearchOptions, hybrid};
+use tempfile::TempDir;
+
+const DIM: usize = 32;
+const N: usize = 3000;
+const CLUSTERS: usize = 20;
+
+struct Rng(u64);
+impl Rng {
+    fn next(&mut self) -> u64 {
+        self.0 = self.0.wrapping_add(0x9E37_79B9_7F4A_7C15);
+        let mut z = self.0;
+        z = (z ^ (z >> 30)).wrapping_mul(0xBF58_476D_1CE4_E5B9);
+        z = (z ^ (z >> 27)).wrapping_mul(0x94D0_49BB_1331_11EB);
+        z ^ (z >> 31)
+    }
+    fn unit(&mut self) -> f32 {
+        (self.next() >> 40) as f32 / (1u64 << 24) as f32 - 0.5
+    }
+}
+
+fn normalize(v: &mut [f32]) {
+    let n = v.iter().map(|x| x * x).sum::<f32>().sqrt();
+    v.iter_mut().for_each(|x| *x /= n);
+}
+
+struct Data {
+    vectors: Vec<Vec<f32>>,
+    cluster: Vec<usize>,
+    centres: Vec<Vec<f32>>,
+}
+
+fn data() -> Data {
+    let mut rng = Rng(42);
+    let centres: Vec<Vec<f32>> = (0..CLUSTERS)
+        .map(|_| {
+            let mut c: Vec<f32> = (0..DIM).map(|_| rng.unit()).collect();
+            normalize(&mut c);
+            c
+        })
+        .collect();
+    let mut vectors = Vec::new();
+    let mut cluster = Vec::new();
+    for i in 0..N {
+        let c = i % CLUSTERS;
+        let mut v: Vec<f32> = centres[c].iter().map(|x| x + rng.unit() * 0.3).collect();
+        normalize(&mut v);
+        vectors.push(v);
+        cluster.push(c);
+    }
+    Data {
+        vectors,
+        cluster,
+        centres,
+    }
+}
+
+/// Channel of record `i` for a filter keeping `percent`% of the store at
+/// random (independent of the vectors).
+fn random_channel(i: usize, rng_seed: u64, percent: u64) -> String {
+    let mut r = Rng(rng_seed ^ (i as u64 * 7919));
+    if r.next() % 100 < percent {
+        "keep".into()
+    } else {
+        "other".into()
+    }
+}
+
+fn build(data: &Data, channel: impl Fn(usize) -> String) -> (TempDir, HDF5Memory) {
+    let dir = TempDir::new().unwrap();
+    let mut cfg = MemoryConfig::new(dir.path().join("s.h5"), "agent", DIM);
+    cfg.hebbian_boost = 0.0; // every query sees the same store
+    let mut m = HDF5Memory::create(cfg).unwrap();
+    let entries = data
+        .vectors
+        .iter()
+        .enumerate()
+        .map(|(i, v)| MemoryEntry {
+            chunk: format!("record {i} cluster {}", data.cluster[i]),
+            embedding: v.clone(),
+            source_channel: channel(i),
+            timestamp: i as f64,
+            session_id: "s".into(),
+            tags: format!("t{i}"),
+        })
+        .collect();
+    m.save_batch(entries).unwrap();
+    (dir, m)
+}
+
+/// Exact top-k by cosine among the records `allowed` keeps.
+fn exact_top(data: &Data, q: &[f32], k: usize, allowed: impl Fn(usize) -> bool) -> Vec<usize> {
+    let mut s: Vec<(usize, f32)> = (0..N)
+        .filter(|&i| allowed(i))
+        .map(|i| (i, data.vectors[i].iter().zip(q).map(|(a, b)| a * b).sum()))
+        .collect();
+    s.sort_by(|a, b| b.1.total_cmp(&a.1).then(a.0.cmp(&b.0)));
+    s.into_iter().take(k).map(|(i, _)| i).collect()
+}
+
+fn query(data: &Data, i: usize) -> Vec<f32> {
+    let mut rng = Rng(1000 + i as u64);
+    let mut q: Vec<f32> = data.centres[i % CLUSTERS]
+        .iter()
+        .map(|x| x + rng.unit() * 0.3)
+        .collect();
+    normalize(&mut q);
+    q
+}
+
+fn vector_only(k: usize) -> SearchOptions {
+    SearchOptions::new(k).with_fusion(hybrid::Fusion::Weighted {
+        vector: 1.0,
+        keyword: 0.0,
+    })
+}
+
+#[test]
+fn source_filter_returns_only_allowed_records_and_a_full_page() {
+    let d = data();
+    // At N = 3000 and k = 10 the index serves a filter only when that is
+    // cheaper than scanning the allowed records: pool = 80 * N / allowed
+    // candidates at ~M = 16 distances each, against `allowed` distances. So
+    // 90% goes through the index, 50% and 1% to the exact scan.
+    for percent in [90, 50, 1] {
+        let (_dir, mut m) = build(&d, |i| random_channel(i, 5, percent));
+        let allowed = |i: usize| random_channel(i, 5, percent) == "keep";
+        let mut hits = 0;
+        for qi in 0..40 {
+            let q = query(&d, qi);
+            let got = m.search(&q, "", &vector_only(10).with_sources(["keep"]));
+            assert_eq!(got.len(), 10, "{percent}%: short page");
+            assert!(got.iter().all(|r| r.source_channel == "keep"));
+            let want: HashSet<usize> = exact_top(&d, &q, 10, allowed).into_iter().collect();
+            hits += got.iter().filter(|r| want.contains(&r.index)).count();
+        }
+        let recall = hits as f64 / 400.0;
+        let floor = if percent == 90 { 0.95 } else { 1.0 };
+        assert!(recall >= floor, "{percent}%: recall@10 {recall}");
+    }
+}
+
+#[test]
+fn filter_away_from_the_query_falls_back_to_an_exact_scan() {
+    // Channel = cluster, and the filter keeps two clusters (10% of the
+    // store) that are not the query's: the index's neighbourhood of the
+    // query holds none of them. The search must still return the exact
+    // top 10 among the allowed records, not a short or empty page.
+    let d = data();
+    let (_dir, mut m) = build(&d, |i| format!("c{}", d.cluster[i]));
+    for qi in 0..20 {
+        let q = query(&d, qi);
+        let a = format!("c{}", (qi + 7) % CLUSTERS);
+        let b = format!("c{}", (qi + 13) % CLUSTERS);
+        let got: Vec<usize> = m
+            .search(
+                &q,
+                "",
+                &vector_only(10).with_sources([a.clone(), b.clone()]),
+            )
+            .iter()
+            .map(|r| r.index)
+            .collect();
+        let want = exact_top(&d, &q, 10, |i| {
+            let c = format!("c{}", d.cluster[i]);
+            c == a || c == b
+        });
+        assert_eq!(got, want, "query {qi}");
+    }
+}
+
+#[test]
+fn filter_edge_cases() {
+    let d = data();
+    let (_dir, mut m) = build(&d, |i| random_channel(i, 9, 50));
+    let q = query(&d, 0);
+    assert!(
+        m.search(
+            &q,
+            "cluster",
+            &SearchOptions::new(10).with_sources(Vec::<String>::new())
+        )
+        .is_empty()
+    );
+    assert!(
+        m.search(
+            &q,
+            "cluster",
+            &SearchOptions::new(10).with_sources(["nope"])
+        )
+        .is_empty()
+    );
+    // Keyword matches from other channels are filtered too.
+    let got = m.search(
+        &q,
+        "record cluster",
+        &SearchOptions::new(50).with_sources(["keep"]),
+    );
+    assert_eq!(got.len(), 50);
+    assert!(got.iter().all(|r| r.source_channel == "keep"));
+    // Deleted records never come back, filtered or not.
+    let first = got[0].index;
+    m.delete(first).unwrap();
+    let again = m.search(
+        &q,
+        "record cluster",
+        &SearchOptions::new(50).with_sources(["keep"]),
+    );
+    assert!(again.iter().all(|r| r.index != first));
+}
+
+#[test]
+fn plain_options_equal_hybrid_search_with() {
+    // Two identical stores, so neither query sees the other's boosts.
+    let d = data();
+    let (_a, mut a) = build(&d, |i| random_channel(i, 3, 50));
+    let (_b, mut b) = build(&d, |i| random_channel(i, 3, 50));
+    for qi in 0..10 {
+        let q = query(&d, qi);
+        let x: Vec<(usize, u32)> = a
+            .search(&q, "record cluster 3", &SearchOptions::new(10))
+            .iter()
+            .map(|r| (r.index, r.score.to_bits()))
+            .collect();
+        let y: Vec<(usize, u32)> = b
+            .hybrid_search_with(&q, "record cluster 3", hybrid::DEFAULT_FUSION, 10)
+            .iter()
+            .map(|r| (r.index, r.score.to_bits()))
+            .collect();
+        assert_eq!(x, y);
+    }
+}
+
+fn small_store(entries: &[(&str, &str, f64)]) -> (TempDir, HDF5Memory) {
+    let dir = TempDir::new().unwrap();
+    let mut m = HDF5Memory::create(MemoryConfig::new(dir.path().join("r.h5"), "a", 4)).unwrap();
+    m.save_batch(
+        entries
+            .iter()
+            .map(|(chunk, channel, ts)| MemoryEntry {
+                chunk: chunk.to_string(),
+                embedding: vec![1.0, 0.0, 0.0, 0.0],
+                source_channel: channel.to_string(),
+                timestamp: *ts,
+                session_id: "s".into(),
+                tags: String::new(),
+            })
+            .collect(),
+    )
+    .unwrap();
+    (dir, m)
+}
+
+#[test]
+fn rerank_breaks_relevance_ties_by_recency() {
+    // Identical text and vectors, so retrieval ties; re-ranking must put the
+    // newer record first and report the combined score.
+    let now = 1_000_000.0;
+    let (_d, mut m) = small_store(&[
+        ("user prefers dark mode", "chat", now - 30.0 * 86_400.0),
+        ("user prefers dark mode", "chat", now - 60.0),
+    ]);
+    let q = [1.0, 0.0, 0.0, 0.0];
+    let plain = m.search(&q, "dark mode", &SearchOptions::new(2));
+    assert_eq!(plain[0].index, 0, "ties break by index without re-ranking");
+    let reranked = m.search(
+        &q,
+        "dark mode",
+        &SearchOptions::new(2)
+            .with_rerank(ReRankConfig::default())
+            .at_time(now),
+    );
+    assert_eq!(reranked[0].index, 1);
+    assert!(reranked[0].score > reranked[1].score);
+    assert_ne!(reranked[0].score.to_bits(), plain[0].score.to_bits());
+}
+
+#[test]
+fn confidence_rejects_when_nothing_is_good_enough() {
+    let (_d, mut m) = small_store(&[("alpha", "chat", 0.0), ("beta", "chat", 0.0)]);
+    let q = [1.0, 0.0, 0.0, 0.0];
+    let strict = ConfidenceConfig {
+        min_score: 10.0,
+        ..ConfidenceConfig::default()
+    };
+    assert!(
+        m.search(&q, "alpha", &SearchOptions::new(2).with_confidence(strict))
+            .is_empty()
+    );
+    let lenient = ConfidenceConfig {
+        min_score: 0.0,
+        min_gap: f32::INFINITY,
+        max_results: 1,
+    };
+    assert_eq!(
+        m.search(&q, "alpha", &SearchOptions::new(2).with_confidence(lenient))
+            .len(),
+        1
+    );
+}
+
+#[test]
+fn only_returned_results_are_reinforced() {
+    // With re-ranking, a pool of max(3k, 10) candidates is retrieved; only
+    // the k returned should gain activation.
+    let d = data();
+    let dir = TempDir::new().unwrap();
+    let path = dir.path().join("h.h5");
+    let mut m = HDF5Memory::create(MemoryConfig::new(path, "a", DIM)).unwrap();
+    m.save_batch(
+        (0..200)
+            .map(|i| MemoryEntry {
+                chunk: format!("record {i}"),
+                embedding: d.vectors[i].clone(),
+                source_channel: "chat".into(),
+                timestamp: i as f64,
+                session_id: "s".into(),
+                tags: String::new(),
+            })
+            .collect(),
+    )
+    .unwrap();
+    let q = query(&d, 0);
+    let got = m.search(
+        &q,
+        "record",
+        &SearchOptions::new(3).with_rerank(ReRankConfig::default()),
+    );
+    assert_eq!(got.len(), 3);
+    let returned: HashSet<usize> = got.iter().map(|r| r.index).collect();
+    // A second plain search reports each record's current activation.
+    let all = m.search(&q, "record", &SearchOptions::new(200));
+    for r in &all {
+        let boosted = r.activation > 1.0;
+        assert_eq!(boosted, returned.contains(&r.index), "record {}", r.index);
+    }
+}

crates/clawhdf5-agent/tests/signed_store.rs

@@ -0,0 +1,330 @@
+//! Ed25519-signed checkpoints: `HDF5Memory::set_signing_key` and
+//! `HDF5Memory::verify`.
+
+use std::path::Path;
+
+use clawhdf5_agent::signing::{SigningKey, VerifyReport, VerifyingKey};
+use clawhdf5_agent::storage;
+use clawhdf5_agent::{AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry, MemoryError, schema};
+use tempfile::TempDir;
+
+const DIM: usize = 16;
+
+fn key(seed: u8) -> SigningKey {
+    SigningKey::from_bytes(&[seed; 32])
+}
+
+fn entry(i: usize, chunk: &str) -> MemoryEntry {
+    MemoryEntry {
+        chunk: chunk.to_string(),
+        embedding: (0..DIM)
+            .map(|j| ((i * DIM + j) as f32 * 0.37).sin())
+            .collect(),
+        source_channel: "chat".into(),
+        timestamp: 1_700_000_000.0 + i as f64,
+        session_id: format!("s{}", i % 3),
+        tags: format!("t{i}"),
+    }
+}
+
+/// Awkward strings on purpose: they must hash the same after a round trip.
+const TEXTS: [&str; 6] = [
+    "plain text",
+    "ünïcödé — 日本語 🙂",
+    "",
+    "trailing spaces   ",
+    "tab\tand\nnewline",
+    "x",
+];
+
+fn signed_store(dir: &TempDir, float16: bool, k: &SigningKey) -> std::path::PathBuf {
+    let mut cfg = MemoryConfig::new(dir.path().join("s.h5"), "agent", DIM);
+    cfg.float16 = float16;
+    let path = cfg.path.clone();
+    let mut m = HDF5Memory::create(cfg).unwrap();
+    m.set_signing_key(k.clone());
+    let entries = (0..30).map(|i| entry(i, TEXTS[i % TEXTS.len()])).collect();
+    m.save_batch(entries).unwrap();
+    // Some graph and a deleted record, so every part of the manifest is used.
+    let a = m.knowledge_mut().add_entity("Alice", "person", 0);
+    let b = m.knowledge_mut().add_entity("Acme", "org", -1);
+    m.knowledge_mut().add_relation(a, b, "works_at", 0.75);
+    m.sessions_mut()
+        .add_at("s0", 0, 9, "chat", "first session", 1_700_000_000.0);
+    m.delete(4).unwrap();
+    m.flush_wal().unwrap();
+    path
+}
+
+fn verify(path: &Path, k: &SigningKey) -> VerifyReport {
+    HDF5Memory::verify(path, &k.verifying_key()).unwrap()
+}
+
+#[test]
+fn a_signed_store_verifies_through_reopen_and_checkpoint_cycles() {
+    for float16 in [true, false] {
+        let dir = TempDir::new().unwrap();
+        let k = key(7);
+        let path = signed_store(&dir, float16, &k);
+        let r = verify(&path, &k);
+        assert!(r.is_valid(), "float16={float16}: {r:?}");
+        assert_eq!(r.public_key, Some(k.verifying_key().to_bytes()));
+        assert_eq!(r.record_count, 30);
+        assert!(r.changed_records.is_empty());
+
+        // Reopen, change nothing, checkpoint again (with the key): still valid.
+        for _ in 0..3 {
+            let mut m = HDF5Memory::open(&path).unwrap();
+            assert!(m.is_signed());
+            m.set_signing_key(k.clone());
+            m.flush_wal().unwrap();
+            drop(m);
+            assert!(verify(&path, &k).is_valid());
+        }
+        // And after real changes, re-signed.
+        let mut m = HDF5Memory::open(&path).unwrap();
+        m.set_signing_key(k.clone());
+        m.save(entry(99, "added later")).unwrap();
+        m.hybrid_search(&entry(1, "").embedding, "text", 0.4, 0.6, 5);
+        m.flush_wal().unwrap();
+        drop(m);
+        let r = verify(&path, &k);
+        assert!(r.is_valid(), "{r:?}");
+        assert_eq!(r.record_count, 31);
+    }
+}
+
+#[test]
+fn a_signed_store_refuses_to_checkpoint_without_its_key() {
+    let dir = TempDir::new().unwrap();
+    let k = key(1);
+    let path = signed_store(&dir, true, &k);
+
+    let mut m = HDF5Memory::open(&path).unwrap();
+    m.save(entry(50, "pending")).unwrap();
+    match m.flush_wal() {
+        Err(MemoryError::SigningKeyRequired(msg)) => assert!(msg.contains("signed"), "{msg}"),
+        other => panic!("expected SigningKeyRequired, got {other:?}"),
+    }
+    // The file is untouched and still valid; the save is still in the WAL.
+    let r = verify(&path, &k);
+    assert!(r.is_valid());
+    assert_eq!(r.wal_entries_unsigned, 1);
+
+    // Supplying the key lets the checkpoint through, signed.
+    m.set_signing_key(k.clone());
+    m.flush_wal().unwrap();
+    drop(m);
+    let r = verify(&path, &k);
+    assert!(r.is_valid());
+    assert_eq!((r.record_count, r.wal_entries_unsigned), (31, 0));
+
+    // Removing the signature on purpose writes it unsigned.
+    let mut m = HDF5Memory::open(&path).unwrap();
+    m.remove_signature();
+    m.flush_wal().unwrap();
+    drop(m);
+    let r = verify(&path, &k);
+    assert!(!r.signed && !r.is_valid());
+    assert!(!HDF5Memory::open(&path).unwrap().is_signed());
+}
+
+#[test]
+fn the_wrong_key_does_not_verify_and_a_new_key_re_signs() {
+    let dir = TempDir::new().unwrap();
+    let (a, b) = (key(1), key(2));
+    let path = signed_store(&dir, true, &a);
+    let r = verify(&path, &b);
+    assert!(r.signed && !r.key_matches && !r.signature_valid && !r.is_valid());
+
+    let mut m = HDF5Memory::open(&path).unwrap();
+    m.set_signing_key(b.clone());
+    m.flush_wal().unwrap();
+    drop(m);
+    assert!(verify(&path, &b).is_valid());
+    assert!(!verify(&path, &a).is_valid());
+}
+
+/// Rewrite the store with changed contents but the *old* signature — what
+/// someone with write access to the file, but not the key, can do.
+fn tamper(path: &Path, change: impl FnOnce(&mut Tampered)) {
+    let file = clawhdf5::File::open(path).unwrap();
+    let (config, cache, sessions, knowledge) = schema::validate_and_load(&file).unwrap();
+    let checkpoint = schema::read_checkpoint_meta(&file);
+    let signature = schema::read_signature(&file).unwrap().unwrap();
+    drop(file);
+    let mut t = Tampered {
+        config,
+        cache,
+        sessions,
+        knowledge,
+    };
+    change(&mut t);
+    storage::write_to_disk_signed(
+        path,
+        &t.config,
+        &t.cache,
+        &t.sessions,
+        &t.knowledge,
+        &checkpoint,
+        Some(&signature),
+    )
+    .unwrap();
+}
+
+struct Tampered {
+    config: MemoryConfig,
+    cache: clawhdf5_agent::cache::MemoryCache,
+    sessions: clawhdf5_agent::SessionCache,
+    knowledge: clawhdf5_agent::knowledge::KnowledgeCache,
+}
+
+#[test]
+fn every_kind_of_edit_is_detected_and_located() {
+    let k = key(3);
+    type Edit = Box<dyn FnOnce(&mut Tampered)>;
+    type Case = (&'static str, Edit, fn(&VerifyReport) -> bool);
+    let cases: Vec<Case> = vec![
+        (
+            "record text",
+            Box::new(|t: &mut Tampered| t.cache.chunks[7] = "rewritten".into()),
+            |r| !r.records_match && r.changed_records == vec![7],
+        ),
+        (
+            "one embedding value",
+            Box::new(|t: &mut Tampered| {
+                let mut e = t.cache.embeddings[12].to_vec();
+                e[3] = 0.5;
+                t.cache.embeddings.set(12, &e);
+            }),
+            |r| r.changed_records == vec![12],
+        ),
+        (
+            "undelete",
+            Box::new(|t: &mut Tampered| t.cache.tombstones[4] = 0),
+            |r| r.changed_records == vec![4],
+        ),
+        (
+            "timestamp",
+            Box::new(|t: &mut Tampered| t.cache.timestamps[20] += 1.0),
+            |r| r.changed_records == vec![20],
+        ),
+        (
+            "record appended",
+            Box::new(|t: &mut Tampered| {
+                t.cache.push(
+                    "new".into(),
+                    vec![0.1; DIM],
+                    "x".into(),
+                    1.0,
+                    "s".into(),
+                    "".into(),
+                );
+            }),
+            |r| !r.records_match && r.changed_records == vec![30] && r.record_count == 31,
+        ),
+        (
+            "setting",
+            Box::new(|t: &mut Tampered| t.config.agent_id = "someone-else".into()),
+            |r| !r.settings_match && r.records_match,
+        ),
+        (
+            "session summary",
+            Box::new(|t: &mut Tampered| t.sessions.summaries[0] = "edited".into()),
+            |r| !r.sessions_match && r.records_match,
+        ),
+        (
+            "graph edge",
+            Box::new(|t: &mut Tampered| t.knowledge.relations[0].weight = 1.0),
+            |r| !r.graph_match && r.records_match,
+        ),
+    ];
+    for (name, edit, check) in cases {
+        let dir = TempDir::new().unwrap();
+        let path = signed_store(&dir, true, &k);
+        tamper(&path, edit);
+        let r = verify(&path, &k);
+        assert!(
+            r.signed && r.key_matches && r.signature_valid,
+            "{name}: {r:?}"
+        );
+        assert!(!r.is_valid(), "{name}: edit not detected: {r:?}");
+        assert!(check(&r), "{name}: {r:?}");
+    }
+}
+
+#[test]
+fn a_forged_manifest_fails_the_signature() {
+    // Recomputing the hashes for tampered contents does not help without the
+    // key: the signature no longer matches the manifest.
+    let dir = TempDir::new().unwrap();
+    let k = key(5);
+    let path = signed_store(&dir, true, &k);
+    let file = clawhdf5::File::open(&path).unwrap();
+    let (config, mut cache, sessions, knowledge) = schema::validate_and_load(&file).unwrap();
+    let checkpoint = schema::read_checkpoint_meta(&file);
+    let mut sig = schema::read_signature(&file).unwrap().unwrap();
+    drop(file);
+    cache.chunks[0] = "forged".into();
+    // Re-sign with an attacker key, then splice the victim's public key back.
+    let forged = clawhdf5_agent::signing::sign(
+        &key(66),
+        &config,
+        &cache,
+        &sessions,
+        &knowledge,
+        checkpoint.wal_applied,
+    );
+    sig.manifest = forged.manifest;
+    sig.record_hashes = forged.record_hashes;
+    storage::write_to_disk_signed(
+        &path,
+        &config,
+        &cache,
+        &sessions,
+        &knowledge,
+        &checkpoint,
+        Some(&sig),
+    )
+    .unwrap();
+    let r = verify(&path, &k);
+    assert!(
+        r.key_matches && !r.signature_valid && !r.is_valid(),
+        "{r:?}"
+    );
+}
+
+#[test]
+fn an_unsigned_store_reports_unsigned() {
+    let dir = TempDir::new().unwrap();
+    let mut m = HDF5Memory::create(MemoryConfig::new(dir.path().join("u.h5"), "a", DIM)).unwrap();
+    m.save_batch(vec![entry(0, "hello")]).unwrap();
+    drop(m);
+    let r = HDF5Memory::verify(&dir.path().join("u.h5"), &VerifyingKey::from(&key(1))).unwrap();
+    assert!(!r.signed && !r.is_valid());
+    assert_eq!(r.record_count, 1);
+}
+
+#[test]
+fn nul_bytes_in_text_still_verify() {
+    // Strings are stored null-padded; the hash must follow what a reopened
+    // store actually holds, or an untouched store would fail to verify.
+    let dir = TempDir::new().unwrap();
+    let k = key(9);
+    let mut m = HDF5Memory::create(MemoryConfig::new(dir.path().join("n.h5"), "a", DIM)).unwrap();
+    m.set_signing_key(k.clone());
+    m.save_batch(vec![
+        entry(0, "inner\0nul"),
+        entry(1, "trailing nul\0"),
+        entry(2, "\0leading"),
+    ])
+    .unwrap();
+    drop(m);
+    let r = verify(&dir.path().join("n.h5"), &k);
+    assert!(r.is_valid(), "{r:?}");
+    let m = HDF5Memory::open(&dir.path().join("n.h5")).unwrap();
+    eprintln!(
+        "reloaded: {:?}",
+        (0..3).map(|i| m.get_chunk(i)).collect::<Vec<_>>()
+    );
+}

crates/clawhdf5-android/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-android"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "Android JNI bridge for edgehdf5-memory HDF5 backend"
 license = "MIT"
 

crates/clawhdf5-ann/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-ann"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "HNSW approximate nearest neighbor index stored as HDF5"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
@@ -10,9 +11,9 @@ keywords = ["hdf5", "ann", "hnsw", "nearest-neighbor"]
 categories = ["algorithms", "science"]
 
 [dependencies]
-clawhdf5-format = { path = "../clawhdf5-format", version = "2.6.0" }
-clawhdf5-io = { path = "../clawhdf5-io", version = "2.6.0" }
-clawhdf5-accel = { path = "../clawhdf5-accel", version = "2.6.0" }
+clawhdf5-format = { path = "../clawhdf5-format", version = "2.7.0" }
+clawhdf5-io = { path = "../clawhdf5-io", version = "2.7.0" }
+clawhdf5-accel = { path = "../clawhdf5-accel", version = "2.7.0" }
 rayon = { version = "1", optional = true }
 
 [features]

crates/clawhdf5-ann/src/hnsw.rs

@@ -13,7 +13,7 @@ use clawhdf5_format::filter_pipeline::FilterPipeline;
 use clawhdf5_format::group_v2::resolve_path_any;
 use clawhdf5_format::message_type::MessageType;
 use clawhdf5_format::object_header::ObjectHeader;
-use clawhdf5_format::signature::find_signature;
+use clawhdf5_format::signature::split_user_block;
 use clawhdf5_format::superblock::Superblock;
 use clawhdf5_io::FileWriter as IoFileWriter;
 
@@ -358,31 +358,12 @@ enum Query {
     Int8(Vec<i8>, f32),
 }
 
-/// Sum of products, widened so it cannot overflow: `dim` terms of at most
-/// `127 * 127`, so `i32` suffices for any realistic dimension.
+/// Sum of products, widened so it cannot overflow. Runtime-dispatched to the
+/// same SIMD backend as the f32 kernels, so the two storages are compared on
+/// equal terms.
+#[inline]
 fn dot_i8(a: &[i8], b: &[i8]) -> i32 {
-    // Four independent accumulators over 32-lane blocks: the widening product
-    // has to sit in a fixed-length chunk for the vectoriser to see it, and the
-    // separate accumulators keep it off one dependency chain.
-    const LANE: usize = 8;
-    let (a_blocks, a_tail) = a.as_chunks::<{ LANE * 4 }>();
-    let (b_blocks, b_tail) = b.as_chunks::<{ LANE * 4 }>();
-    let mut acc = [0i32; 4];
-    for (x, y) in a_blocks.iter().zip(b_blocks) {
-        for (lane, slot) in acc.iter_mut().enumerate() {
-            let mut sum = 0i32;
-            for k in 0..LANE {
-                sum += i32::from(x[lane * LANE + k]) * i32::from(y[lane * LANE + k]);
-            }
-            *slot += sum;
-        }
-    }
-    let tail: i32 = a_tail
-        .iter()
-        .zip(b_tail)
-        .map(|(&x, &y)| i32::from(x) * i32::from(y))
-        .sum();
-    acc[0] + acc[1] + acc[2] + acc[3] + tail
+    clawhdf5_accel::dot_i8(a, b)
 }
 
 /// Magic for [`HnswIndex::graph_to_bytes`].
@@ -880,8 +861,9 @@ impl HnswIndex {
     /// The HDF5 data must contain the `/ann/vectors`, `/ann/graph_layer_*`,
     /// and `/ann/config` datasets as produced by [`to_hdf5_bytes`].
     pub fn load_from_hdf5(data: &[u8]) -> Result<Self, FormatError> {
-        let sig_offset = find_signature(data)?;
-        let sb = Superblock::parse(data, sig_offset)?;
+        // Addresses are relative to the superblock: skip any user block.
+        let (_, data) = split_user_block(data)?;
+        let sb = Superblock::parse(data, 0)?;
 
         // Read config dataset and its attributes
         let config_attrs = read_dataset_attrs(data, &sb, "ann/config")?;

crates/clawhdf5-bench/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-bench"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "Benchmark harnesses for clawhdf5-agent (Track 8)"
 license = "MIT"
 
@@ -33,6 +34,10 @@ path = "src/bin/consolidation_efficiency.rs"
 name = "ephemeral_perf"
 path = "src/bin/ephemeral_perf.rs"
 
+[[bin]]
+name = "concurrent_read"
+path = "src/bin/concurrent_read.rs"
+
 [[bin]]
 name = "mpi_io_bench"
 path = "src/bin/mpi_io_bench.rs"
@@ -63,6 +68,10 @@ clawhdf5-io = { path = "../clawhdf5-io" }
 mpi = { version = "0.8", optional = true }
 serde = { workspace = true }
 serde_json = "1"
+# concurrent_read: size the decode pool (--decode-threads) and evict files
+# from the page cache (--cold, posix_fadvise). Both pure Rust / bindings only.
+rayon = "1"
+libc = "0.2"
 tempfile = { workspace = true }
 # Optional: libhdf5 C wrapper for side-by-side comparison (requires system libhdf5).
 # Enable with: cargo bench -p clawhdf5-bench --features libhdf5-compare

crates/clawhdf5-bench/scripts/compare_concurrent_read.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+"""Tabulate concurrent_read JSON results (clawhdf5, h5py threads/processes).
+
+    python compare_concurrent_read.py clawhdf5.json h5py-threads.json h5py-procs.json
+
+Prints one Markdown table: for each layout, mode and thread count, every
+tool's MB/s and scaling efficiency, and the first file's MB/s relative to each
+of the others. Refuses to compare runs whose workload parameters differ.
+"""
+
+import json
+import sys
+
+COMPARED = ("datasets", "rows", "cols", "chunk", "deflate_level", "slab", "slabs", "seed")
+
+
+def main(paths):
+    if len(paths) < 2:
+        sys.exit(__doc__)
+    docs = []
+    for p in paths:
+        with open(p) as fh:
+            docs.append(json.load(fh))
+    ref = docs[0]
+    for d, p in zip(docs[1:], paths[1:]):
+        diff = [k for k in COMPARED if d["params"].get(k) != ref["params"].get(k)]
+        if diff:
+            sys.exit(f"{p}: workload differs from {paths[0]} in {', '.join(diff)}")
+        if d["cache"] != ref["cache"]:
+            print(f"warning: {p} ran {d['cache']!r}, {paths[0]} ran {ref['cache']!r}",
+                  file=sys.stderr)
+        if d.get("host") != ref.get("host"):
+            print(f"warning: {p} ran on {d.get('host')}, {paths[0]} on {ref.get('host')}",
+                  file=sys.stderr)
+
+    names = [d["tool"] for d in docs]
+    for d in docs:
+        extra = f", HDF5 {d['hdf5_version']}" if "hdf5_version" in d else ""
+        print(f"- {d['tool']} {d['version']}{extra}: host {d.get('host')}, "
+              f"{d.get('cpus')} CPUs, cache {d['cache']}, decode threads per read "
+              f"{d.get('decode_threads')}")
+    p = ref["params"]
+    print(f"\n{p['datasets']} datasets of {p['rows']} x {p['cols']} f32, chunks "
+          f"{p['chunk'][0]} x {p['chunk'][1]} (deflate {p['deflate_level']}); "
+          f"`same`: {p['slabs']} slabs of {p['slab']} x {p['slab']}\n")
+
+    index = [{(r["layout"], r["mode"], r["threads"]): r for r in d["results"]} for d in docs]
+    keys = [(r["layout"], r["mode"], r["threads"]) for r in ref["results"]]
+
+    head = ["layout", "mode", "threads"]
+    head += [f"{n} MB/s (eff)" for n in names]
+    head += [f"{names[0]} / {n}" for n in names[1:]]
+    print("| " + " | ".join(head) + " |")
+    print("|---|---|" + "---:|" * (len(head) - 2))
+    for key in keys:
+        cells = [key[0], key[1], str(key[2])]
+        rs = [ix.get(key) for ix in index]
+        for r in rs:
+            if r is None:
+                cells.append("-")
+            else:
+                eff = "-" if r["efficiency"] is None else f"{r['efficiency']:.2f}"
+                cells.append(f"{r['mb_s']:.0f} ({eff})")
+        for r in rs[1:]:
+            cells.append("-" if r is None else f"{rs[0]['mb_s'] / r['mb_s']:.2f}x")
+        print("| " + " | ".join(cells) + " |")
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])

crates/clawhdf5-bench/scripts/concurrent_read_h5py.py

@@ -0,0 +1,265 @@
+#!/usr/bin/env python3
+"""The concurrent_read workload with h5py, on the files concurrent_read wrote.
+
+libhdf5 serialises every API call under one global lock, and h5py holds its
+own global lock around every call as well, so h5py *threads* cannot decode in
+parallel. h5py users scale with *processes* instead; ``--executor processes``
+measures that (each worker opens the file itself).
+
+The workload mirrors ``crates/clawhdf5-bench/src/bin/concurrent_read.rs``:
+
+* ``distinct``: every dataset read in full once per repetition; worker ``t``
+  of ``T`` reads datasets ``t, t + T, ...``.
+* ``same``: ``--slabs`` random ``--slab`` x ``--slab`` hyperslabs of ``d00``
+  (slab ``j`` to worker ``j % T``), offsets from the same splitmix64 stream.
+
+Each worker times itself from a start barrier; a repetition spans the earliest
+start to the latest finish (CLOCK_MONOTONIC, comparable across processes).
+Threads share one ``h5py.File`` per repetition; process workers open the file
+inside the timed region (a few ms against reads of many MiB).
+
+Generate the files first with the Rust harness (it writes ``manifest.json``),
+then, for example::
+
+    python concurrent_read_h5py.py --dir DIR --executor threads --json h5py-threads.json
+    python concurrent_read_h5py.py --dir DIR --executor processes --json h5py-procs.json
+"""
+
+import argparse
+import json
+import multiprocessing as mp
+import os
+import platform
+import socket
+import sys
+import threading
+import time
+
+import h5py
+import numpy as np
+
+M64 = (1 << 64) - 1
+
+
+def splitmix64(state):
+    """Return (new_state, value); the same stream as the Rust harness."""
+    state = (state + 0x9E3779B97F4A7C15) & M64
+    z = state
+    z = ((z ^ (z >> 30)) * 0xBF58476D1CE4E5B9) & M64
+    z = ((z ^ (z >> 27)) * 0x94D049BB133111EB) & M64
+    return state, z ^ (z >> 31)
+
+
+def value(k, i):
+    """Element i (row-major) of dataset k, exactly as concurrent_read writes it."""
+    _, noise = splitmix64(i ^ (k << 40))
+    return np.float32((((i >> 6) % 16384) + k) + (noise & 0xFF) / 256.0)
+
+
+def slab_offsets(seed, count, rows, cols, slab):
+    s = seed
+    out = []
+    for _ in range(count):
+        s, r = splitmix64(s)
+        s, c = splitmix64(s)
+        out.append((r % (rows - slab + 1), c % (cols - slab + 1)))
+    return out
+
+
+def now():
+    return time.clock_gettime(time.CLOCK_MONOTONIC)
+
+
+def work(f, mode, t, threads, m, slabs, slab, verify):
+    """Worker t's share of one repetition on an open h5py.File."""
+    n = m["rows"] * m["cols"]
+    if mode == "distinct":
+        for k in range(t, m["datasets"], threads):
+            got = f[f"d{k:02d}"][...]
+            assert got.size == n
+            if verify:
+                flat = got.reshape(-1)
+                for i in (0, n // 3, n - 1):
+                    assert flat[i] == value(k, i), f"d{k:02d}[{i}]"
+    else:
+        ds = f["d00"]
+        cols = m["cols"]
+        for r, c in slabs[t::threads]:
+            got = ds[r : r + slab, c : c + slab]
+            assert got.shape == (slab, slab)
+            if verify:
+                assert got[0, 0] == value(0, r * cols + c)
+                last = (r + slab - 1) * cols + c + slab - 1
+                assert got[-1, -1] == value(0, last)
+
+
+# ----- process workers ------------------------------------------------------
+
+_barrier = None
+
+
+def _init(barrier):
+    global _barrier
+    _barrier = barrier
+
+
+def _proc_task(task):
+    path, mode, t, threads, m, slabs, slab = task
+    _barrier.wait()
+    start = now()
+    with h5py.File(path, "r") as f:
+        work(f, mode, t, threads, m, slabs, slab, False)
+    return start, now()
+
+
+def _noop(_):
+    return os.getpid()
+
+
+def run_threads(path, mode, threads, m, slabs, slab):
+    spans = [None] * threads
+    barrier = threading.Barrier(threads)
+    with h5py.File(path, "r") as f:
+
+        def body(t):
+            barrier.wait()
+            start = now()
+            work(f, mode, t, threads, m, slabs, slab, False)
+            spans[t] = (start, now())
+
+        ts = [threading.Thread(target=body, args=(t,)) for t in range(threads)]
+        for th in ts:
+            th.start()
+        for th in ts:
+            th.join()
+    return max(e for _, e in spans) - min(s for s, _ in spans)
+
+
+def run_processes(pool, path, mode, threads, m, slabs, slab):
+    tasks = [(path, mode, t, threads, m, slabs, slab) for t in range(threads)]
+    # One task per worker: each blocks in the barrier until all T have
+    # started, so no worker can take a second task.
+    spans = pool.map(_proc_task, tasks, chunksize=1)
+    return max(e for _, e in spans) - min(s for s, _ in spans)
+
+
+def warm(path):
+    with open(path, "rb") as fh:
+        while fh.read(1 << 24):
+            pass
+
+
+def evict(path):
+    fd = os.open(path, os.O_RDONLY)
+    try:
+        os.posix_fadvise(fd, 0, 0, os.POSIX_FADV_DONTNEED)
+    finally:
+        os.close(fd)
+
+
+def main():
+    ap = argparse.ArgumentParser(description=__doc__.split("\n\n")[0])
+    ap.add_argument("--dir", default="concurrent-read-data")
+    ap.add_argument("--executor", choices=["threads", "processes"], default="threads")
+    ap.add_argument("--threads", default="1,2,4,8,16")
+    ap.add_argument("--reps", type=int, default=3)
+    ap.add_argument("--slab", type=int, default=256)
+    ap.add_argument("--slabs", type=int, default=1024)
+    ap.add_argument("--seed", type=int, default=42)
+    ap.add_argument("--cold", action="store_true")
+    ap.add_argument("--modes", default="distinct,same")
+    ap.add_argument("--layouts", default="deflate,contiguous")
+    ap.add_argument("--json")
+    a = ap.parse_args()
+
+    # The Rust harness pins this value (splitmix64_reference).
+    assert splitmix64(42)[1] == 0xBDD732262FEB6E95, "splitmix64 port is wrong"
+
+    try:
+        with open(os.path.join(a.dir, "manifest.json")) as fh:
+            m = json.load(fh)
+    except FileNotFoundError:
+        sys.exit(f"{a.dir}/manifest.json not found: generate the files with "
+                 "`cargo run --release -p clawhdf5-bench --bin concurrent_read -- --dir ...` first")
+    threads_list = [int(x) for x in a.threads.split(",")]
+    modes = a.modes.split(",")
+    layouts = a.layouts.split(",")
+    if a.slab < 1 or a.slab > min(m["rows"], m["cols"]):
+        sys.exit(f"--slab must be 1..={min(m['rows'], m['cols'])}")
+    files = dict(m["files"])
+    slabs = slab_offsets(a.seed, a.slabs, m["rows"], m["cols"], a.slab)
+    dataset_bytes = m["rows"] * m["cols"] * 4
+    tool = f"h5py-{a.executor}"
+
+    ctx = mp.get_context("spawn")  # never fork a process holding HDF5 state
+    pools = {}
+    if a.executor == "processes":
+        for t in threads_list:
+            pool = ctx.Pool(t, initializer=_init, initargs=(ctx.Barrier(t),))
+            pool.map(_noop, range(t))  # start the workers outside the timing
+            pools[t] = pool
+
+    rows = []
+    print("| layout | mode | threads | MB/s | efficiency | median s |")
+    print("|---|---|---:|---:|---:|---:|")
+    try:
+        for layout in layouts:
+            path = os.path.join(a.dir, files[layout])
+            if not a.cold:
+                warm(path)
+            for mode in modes:
+                with h5py.File(path, "r") as f:  # untimed, checked pass
+                    work(f, mode, 0, 1, m, slabs, a.slab, True)
+                nbytes = (dataset_bytes * m["datasets"] if mode == "distinct"
+                          else a.slab * a.slab * 4 * a.slabs)
+                base = None
+                for t in threads_list:
+                    times = []
+                    for _ in range(a.reps):
+                        if a.cold:
+                            evict(path)
+                        if a.executor == "threads":
+                            times.append(run_threads(path, mode, t, m, slabs, a.slab))
+                        else:
+                            times.append(run_processes(pools[t], path, mode, t, m, slabs, a.slab))
+                    med = sorted(times)[len(times) // 2]
+                    mb_s = nbytes / (1 << 20) / med
+                    if t == 1:
+                        base = mb_s
+                    eff = mb_s / (t * base) if base else None
+                    print(f"| {layout} | {mode} | {t} | {mb_s:.0f} | "
+                          f"{'-' if eff is None else f'{eff:.2f}'} | {med:.4f} |")
+                    rows.append({
+                        "layout": layout, "mode": mode, "threads": t, "bytes": nbytes,
+                        "times_s": times, "median_s": med, "mb_s": mb_s, "efficiency": eff,
+                    })
+    finally:
+        for pool in pools.values():
+            pool.terminate()
+
+    if a.json:
+        doc = {
+            "tool": tool,
+            "version": h5py.__version__,
+            "hdf5_version": h5py.version.hdf5_version,
+            "python": platform.python_version(),
+            "host": socket.gethostname(),
+            "cpus": os.cpu_count(),
+            "unix_time": int(time.time()),
+            "cache": ("cold (posix_fadvise DONTNEED before each repetition)"
+                      if a.cold else "warm"),
+            "decode_threads": 1,
+            "params": {
+                "datasets": m["datasets"], "rows": m["rows"], "cols": m["cols"],
+                "chunk": m["chunk"], "deflate_level": m["deflate_level"],
+                "mib": dataset_bytes // (1 << 20), "slab": a.slab, "slabs": a.slabs,
+                "seed": a.seed, "reps": a.reps, "dir": a.dir,
+            },
+            "results": rows,
+        }
+        with open(a.json, "w") as fh:
+            json.dump(doc, fh, indent=2)
+
+
+if __name__ == "__main__":
+    main()

crates/clawhdf5-bench/src/bin/concurrent_read.rs

@@ -0,0 +1,523 @@
+//! Concurrent-read harness: how does decoded read throughput scale with the
+//! number of threads reading one open file?
+//!
+//! libhdf5 (threadsafe build) serialises every API call under one global
+//! mutex, and h5py holds it too, so threads cannot decode in parallel there.
+//! A clawhdf5 [`File`] is `Send + Sync`; this harness measures what that buys.
+//! `crates/clawhdf5-bench/scripts/concurrent_read_h5py.py` runs the same
+//! workload on the same files with h5py (threads, and processes), and
+//! `compare_concurrent_read.py` tabulates the JSON both write.
+//!
+//! Files (generated on first use, reused while `manifest.json` matches):
+//!
+//! * `<dir>/deflate.h5`: `--datasets` datasets `d00`, `d01`, ... of `f32`,
+//!   `--mib` MiB decoded each, shape `[mib * 256, 1024]`, chunks `256 x 256`,
+//!   deflate level 4.
+//! * `<dir>/contiguous.h5`: the same datasets, contiguous.
+//!
+//! Modes, for each layout and each thread count `T` (strong scaling: the total
+//! work per repetition is fixed, split among the threads):
+//!
+//! * `distinct`: every dataset is read in full once; thread `t` reads datasets
+//!   `t, t + T, t + 2T, ...`.
+//! * `same`: all threads read `d00`, `--slabs` random `--slab` x `--slab`
+//!   hyperslabs in total (slab `j` goes to thread `j % T`). The offsets come
+//!   from a splitmix64 stream seeded with `--seed`, identical in the h5py
+//!   script.
+//!
+//! One `File` per layout per repetition is shared by all threads (opened
+//! fresh each repetition, so no chunk cache carries over). Page cache:
+//! `warm` (default) reads every file once before timing; `--cold` evicts the
+//! files from the page cache with `posix_fadvise(POSIX_FADV_DONTNEED)` before
+//! every repetition (no root needed; it only evicts clean, unmapped pages, so
+//! it is best effort — the JSON says which was used).
+//!
+//! Decode inside one read is itself parallel when clawhdf5-format's `parallel`
+//! feature is on (it is in this binary, via clawhdf5-agent). `--decode-threads
+//! N` sizes that rayon pool; `--decode-threads 1` measures the API's own
+//! thread scaling, comparable with h5py where each call decodes on the
+//! calling thread.
+//!
+//! ```text
+//! cargo run --release -p clawhdf5-bench --bin concurrent_read -- \
+//!     --dir /data/concurrent-read --json clawhdf5.json
+//! cargo run --release -p clawhdf5-bench --bin concurrent_read -- \
+//!     --dir /tmp/cr --datasets 4 --mib 1 --threads 1,2 --slabs 16 --reps 1   # smoke
+//! ```
+
+use std::path::{Path, PathBuf};
+use std::sync::Barrier;
+use std::time::Instant;
+
+use clawhdf5::{File, FileBuilder, Selection};
+use serde::{Deserialize, Serialize};
+
+const COLS: u64 = 1024;
+const ROWS_PER_MIB: u64 = 256; // 256 rows x 1024 cols x 4 bytes = 1 MiB
+const CHUNK: u64 = 256;
+const DEFLATE_LEVEL: u32 = 4;
+const LAYOUTS: [&str; 2] = ["deflate", "contiguous"];
+const MANIFEST_VERSION: u32 = 1;
+
+/// splitmix64 — shared with the h5py script, which must produce the same
+/// stream (both the data and the hyperslab offsets depend on it).
+fn splitmix64(state: &mut u64) -> u64 {
+    *state = state.wrapping_add(0x9E37_79B9_7F4A_7C15);
+    let mut z = *state;
+    z = (z ^ (z >> 30)).wrapping_mul(0xBF58_476D_1CE4_E5B9);
+    z = (z ^ (z >> 27)).wrapping_mul(0x94D0_49BB_1331_11EB);
+    z ^ (z >> 31)
+}
+
+/// Element `i` (row-major) of dataset `k`: a slowly varying integer part plus
+/// 8 bits of noise, so deflate has real work to do (about 3.1x) and every value
+/// is exact in `f32` (< 2^15 with 8 fraction bits), which lets both harnesses
+/// check what they read against this formula.
+fn value(k: u64, i: u64) -> f32 {
+    let mut s = i ^ (k << 40);
+    let noise = splitmix64(&mut s) & 0xff;
+    (((i >> 6) % 16384) + k) as f32 + noise as f32 / 256.0
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Debug, Clone)]
+struct Manifest {
+    version: u32,
+    datasets: u64,
+    rows: u64,
+    cols: u64,
+    chunk: [u64; 2],
+    deflate_level: u32,
+    files: Vec<(String, String)>, // (layout, file name)
+    writer: String,
+}
+
+fn manifest_for(datasets: u64, mib: u64) -> Manifest {
+    Manifest {
+        version: MANIFEST_VERSION,
+        datasets,
+        rows: mib * ROWS_PER_MIB,
+        cols: COLS,
+        chunk: [CHUNK, CHUNK],
+        deflate_level: DEFLATE_LEVEL,
+        files: LAYOUTS
+            .iter()
+            .map(|l| (l.to_string(), format!("{l}.h5")))
+            .collect(),
+        writer: format!("clawhdf5 {}", env!("CARGO_PKG_VERSION")),
+    }
+}
+
+fn dataset_values(k: u64, n: u64) -> Vec<f32> {
+    (0..n).map(|i| value(k, i)).collect()
+}
+
+/// Write the files unless `dir` already holds ones matching `want`.
+fn ensure_files(dir: &Path, want: &Manifest) -> std::io::Result<bool> {
+    let manifest_path = dir.join("manifest.json");
+    if let Ok(text) = std::fs::read_to_string(&manifest_path)
+        && let Ok(have) = serde_json::from_str::<Manifest>(&text)
+        && have.version == want.version
+        && have.datasets == want.datasets
+        && have.rows == want.rows
+        && have.cols == want.cols
+        && have.chunk == want.chunk
+        && have.deflate_level == want.deflate_level
+        && have.files == want.files
+        && want.files.iter().all(|(_, f)| dir.join(f).exists())
+    {
+        return Ok(false);
+    }
+    std::fs::create_dir_all(dir)?;
+    // A stale manifest must not survive a half-written regeneration.
+    let _ = std::fs::remove_file(&manifest_path);
+    let n = want.rows * want.cols;
+    for (layout, file) in &want.files {
+        // One layout at a time keeps the peak memory to about twice one
+        // file's decoded size.
+        let mut b = FileBuilder::new();
+        for k in 0..want.datasets {
+            let ds = b.create_dataset(&format!("d{k:02}"));
+            ds.with_f32_data(&dataset_values(k, n))
+                .with_shape(&[want.rows, want.cols]);
+            if layout == "deflate" {
+                ds.with_chunks(&[CHUNK.min(want.rows), CHUNK])
+                    .with_deflate(DEFLATE_LEVEL);
+            }
+        }
+        b.write(dir.join(file)).map_err(std::io::Error::other)?;
+    }
+    std::fs::write(
+        &manifest_path,
+        serde_json::to_string_pretty(want).map_err(std::io::Error::other)?,
+    )?;
+    Ok(true)
+}
+
+fn slab_offsets(seed: u64, count: usize, rows: u64, cols: u64, slab: u64) -> Vec<(u64, u64)> {
+    let mut s = seed;
+    (0..count)
+        .map(|_| {
+            let r = splitmix64(&mut s) % (rows - slab + 1);
+            let c = splitmix64(&mut s) % (cols - slab + 1);
+            (r, c)
+        })
+        .collect()
+}
+
+/// Warm the page cache by reading every byte of `path`.
+fn warm(path: &Path) -> std::io::Result<()> {
+    let mut f = std::fs::File::open(path)?;
+    std::io::copy(&mut f, &mut std::io::sink())?;
+    Ok(())
+}
+
+/// Ask the kernel to drop `path`'s pages from the page cache.
+fn evict(path: &Path) -> std::io::Result<()> {
+    use std::os::fd::AsRawFd;
+    let f = std::fs::File::open(path)?;
+    // SAFETY: plain syscall on a valid, open file descriptor.
+    let rc = unsafe { libc::posix_fadvise(f.as_raw_fd(), 0, 0, libc::POSIX_FADV_DONTNEED) };
+    if rc != 0 {
+        return Err(std::io::Error::from_raw_os_error(rc));
+    }
+    Ok(())
+}
+
+#[derive(Serialize)]
+struct Row {
+    layout: String,
+    mode: String,
+    threads: usize,
+    /// Decoded (selected) bytes read per repetition.
+    bytes: u64,
+    times_s: Vec<f64>,
+    median_s: f64,
+    mb_s: f64,
+    /// `mb_s / (threads * mb_s at threads = 1)`; null without a 1-thread row.
+    efficiency: Option<f64>,
+}
+
+struct Args {
+    dir: PathBuf,
+    datasets: u64,
+    mib: u64,
+    threads: Vec<usize>,
+    reps: usize,
+    slab: u64,
+    slabs: usize,
+    seed: u64,
+    cold: bool,
+    decode_threads: usize,
+    modes: Vec<String>,
+    layouts: Vec<String>,
+    json: Option<PathBuf>,
+}
+
+const USAGE: &str = "\
+usage: concurrent_read [--dir DIR] [--datasets N] [--mib N] [--threads 1,2,4,8,16]
+                       [--reps N] [--slab N] [--slabs N] [--seed N] [--cold]
+                       [--decode-threads N] [--modes distinct,same]
+                       [--layouts deflate,contiguous] [--json FILE]";
+
+fn parse_list<T: std::str::FromStr>(s: &str) -> Result<Vec<T>, String> {
+    s.split(',')
+        .map(|x| x.trim().parse().map_err(|_| format!("bad list item {x:?}")))
+        .collect()
+}
+
+fn parse_args() -> Result<Args, String> {
+    let mut a = Args {
+        dir: PathBuf::from("concurrent-read-data"),
+        datasets: 64,
+        mib: 64,
+        threads: vec![1, 2, 4, 8, 16],
+        reps: 3,
+        slab: 256,
+        slabs: 1024,
+        seed: 42,
+        cold: false,
+        decode_threads: 0,
+        modes: vec!["distinct".into(), "same".into()],
+        layouts: LAYOUTS.iter().map(|s| s.to_string()).collect(),
+        json: None,
+    };
+    let mut it = std::env::args().skip(1);
+    while let Some(flag) = it.next() {
+        if flag == "--cold" {
+            a.cold = true;
+            continue;
+        }
+        if flag == "-h" || flag == "--help" {
+            return Err(USAGE.into());
+        }
+        let v = it.next().ok_or(format!("{flag} needs a value\n{USAGE}"))?;
+        let num = |v: &str| {
+            v.parse::<u64>()
+                .map_err(|_| format!("{flag}: bad number {v:?}"))
+        };
+        match flag.as_str() {
+            "--dir" => a.dir = v.into(),
+            "--datasets" => a.datasets = num(&v)?,
+            "--mib" => a.mib = num(&v)?,
+            "--threads" => a.threads = parse_list(&v)?,
+            "--reps" => a.reps = num(&v)? as usize,
+            "--slab" => a.slab = num(&v)?,
+            "--slabs" => a.slabs = num(&v)? as usize,
+            "--seed" => a.seed = num(&v)?,
+            "--decode-threads" => a.decode_threads = num(&v)? as usize,
+            "--modes" => a.modes = parse_list(&v)?,
+            "--layouts" => a.layouts = parse_list(&v)?,
+            "--json" => a.json = Some(v.into()),
+            _ => return Err(format!("unknown flag {flag}\n{USAGE}")),
+        }
+    }
+    if a.datasets == 0 || a.datasets > 100 {
+        return Err("--datasets must be 1..=100".into());
+    }
+    if a.mib == 0 || a.reps == 0 || a.slabs == 0 || a.threads.contains(&0) {
+        return Err("--mib, --reps, --slabs and every --threads value must be > 0".into());
+    }
+    if a.slab == 0 || a.slab > COLS || a.slab > a.mib * ROWS_PER_MIB {
+        return Err(format!(
+            "--slab must be 1..={}",
+            COLS.min(a.mib * ROWS_PER_MIB)
+        ));
+    }
+    for m in &a.modes {
+        if m != "distinct" && m != "same" {
+            return Err(format!("unknown mode {m:?}"));
+        }
+    }
+    for l in &a.layouts {
+        if !LAYOUTS.contains(&l.as_str()) {
+            return Err(format!("unknown layout {l:?}"));
+        }
+    }
+    Ok(a)
+}
+
+/// One timed repetition: `T` threads on one shared `File`. Returns seconds.
+fn run_once(
+    path: &Path,
+    mode: &str,
+    threads: usize,
+    m: &Manifest,
+    slabs: &[(u64, u64)],
+    slab: u64,
+    verify: bool,
+) -> f64 {
+    let file = File::open(path).expect("open");
+    let barrier = Barrier::new(threads + 1); // + the spawning thread
+    let n = m.rows * m.cols;
+    // Each thread times itself from the barrier; the repetition spans the
+    // earliest start to the latest finish (timing on the spawning thread
+    // instead undercounts whenever it is scheduled after the workers ran).
+    let spans: Vec<(Instant, Instant)> = std::thread::scope(|s| {
+        let handles: Vec<_> = (0..threads)
+            .map(|t| {
+                let (file, barrier) = (&file, &barrier);
+                s.spawn(move || {
+                    barrier.wait();
+                    let start = Instant::now();
+                    match mode {
+                        "distinct" => {
+                            for k in (t as u64..m.datasets).step_by(threads) {
+                                let got = file.dataset(&format!("d{k:02}")).unwrap().read_f32();
+                                let got = got.unwrap();
+                                assert_eq!(got.len() as u64, n);
+                                if verify {
+                                    for i in [0, n / 3, n - 1] {
+                                        assert_eq!(got[i as usize], value(k, i), "d{k:02}[{i}]");
+                                    }
+                                }
+                                std::hint::black_box(got);
+                            }
+                        }
+                        _ => {
+                            let ds = file.dataset("d00").unwrap();
+                            for &(r, c) in slabs.iter().skip(t).step_by(threads) {
+                                let sel = Selection::Hyperslab {
+                                    start: vec![r, c],
+                                    stride: vec![1, 1],
+                                    count: vec![slab, slab],
+                                    block: vec![1, 1],
+                                };
+                                let got = ds.read_f32_selection(&sel).unwrap();
+                                assert_eq!(got.len() as u64, slab * slab);
+                                if verify {
+                                    let last = (r + slab - 1) * m.cols + c + slab - 1;
+                                    assert_eq!(got[0], value(0, r * m.cols + c));
+                                    assert_eq!(*got.last().unwrap(), value(0, last));
+                                }
+                                std::hint::black_box(got);
+                            }
+                        }
+                    }
+                    (start, Instant::now())
+                })
+            })
+            .collect();
+        barrier.wait();
+        handles.into_iter().map(|h| h.join().unwrap()).collect()
+    });
+    let start = spans.iter().map(|s| s.0).min().unwrap();
+    let end = spans.iter().map(|s| s.1).max().unwrap();
+    (end - start).as_secs_f64()
+}
+
+fn median(v: &[f64]) -> f64 {
+    let mut s = v.to_vec();
+    s.sort_by(f64::total_cmp);
+    s[s.len() / 2]
+}
+
+fn hostname() -> String {
+    std::fs::read_to_string("/proc/sys/kernel/hostname")
+        .map(|s| s.trim().to_string())
+        .unwrap_or_else(|_| "unknown".into())
+}
+
+fn main() {
+    let args = match parse_args() {
+        Ok(a) => a,
+        Err(e) => {
+            eprintln!("{e}");
+            std::process::exit(2);
+        }
+    };
+    if cfg!(debug_assertions) {
+        eprintln!("warning: debug build — numbers are meaningless. Use --release.");
+    }
+    if args.decode_threads > 0 {
+        rayon::ThreadPoolBuilder::new()
+            .num_threads(args.decode_threads)
+            .build_global()
+            .expect("configure rayon pool");
+    }
+
+    let manifest = manifest_for(args.datasets, args.mib);
+    let t = Instant::now();
+    match ensure_files(&args.dir, &manifest) {
+        Ok(true) => eprintln!(
+            "generated {} in {:.1} s",
+            args.dir.display(),
+            t.elapsed().as_secs_f64()
+        ),
+        Ok(false) => eprintln!("reusing {}", args.dir.display()),
+        Err(e) => {
+            eprintln!("cannot write test files in {}: {e}", args.dir.display());
+            std::process::exit(1);
+        }
+    }
+    let path_of = |layout: &str| args.dir.join(format!("{layout}.h5"));
+    let slabs = slab_offsets(
+        args.seed,
+        args.slabs,
+        manifest.rows,
+        manifest.cols,
+        args.slab,
+    );
+    let dataset_bytes = manifest.rows * manifest.cols * 4;
+
+    let mut rows: Vec<Row> = Vec::new();
+    println!("| layout | mode | threads | MB/s | efficiency | median s |");
+    println!("|---|---|---:|---:|---:|---:|");
+    for layout in &args.layouts {
+        let path = path_of(layout);
+        // Untimed pass: page cache warm (unless --cold), results checked.
+        if !args.cold {
+            warm(&path).expect("warm page cache");
+        }
+        for mode in &args.modes {
+            run_once(&path, mode, 1, &manifest, &slabs, args.slab, true);
+            let bytes = match mode.as_str() {
+                "distinct" => dataset_bytes * manifest.datasets,
+                _ => args.slab * args.slab * 4 * args.slabs as u64,
+            };
+            let mut base: Option<f64> = None;
+            for &threads in &args.threads {
+                let times: Vec<f64> = (0..args.reps)
+                    .map(|_| {
+                        if args.cold {
+                            evict(&path).expect("posix_fadvise");
+                        }
+                        run_once(&path, mode, threads, &manifest, &slabs, args.slab, false)
+                    })
+                    .collect();
+                let med = median(&times);
+                let mb_s = bytes as f64 / (1 << 20) as f64 / med;
+                if threads == 1 {
+                    base = Some(mb_s);
+                }
+                let efficiency = base.map(|b| mb_s / (threads as f64 * b));
+                println!(
+                    "| {layout} | {mode} | {threads} | {mb_s:.0} | {} | {med:.4} |",
+                    efficiency.map_or("-".into(), |e| format!("{e:.2}"))
+                );
+                rows.push(Row {
+                    layout: layout.clone(),
+                    mode: mode.clone(),
+                    threads,
+                    bytes,
+                    times_s: times,
+                    median_s: med,
+                    mb_s,
+                    efficiency,
+                });
+            }
+        }
+    }
+
+    if let Some(out) = &args.json {
+        let doc = serde_json::json!({
+            "tool": "clawhdf5",
+            "version": env!("CARGO_PKG_VERSION"),
+            "host": hostname(),
+            "cpus": std::thread::available_parallelism().map_or(0, |n| n.get()),
+            "unix_time": std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .map_or(0, |d| d.as_secs()),
+            "cache": if args.cold { "cold (posix_fadvise DONTNEED before each repetition)" } else { "warm" },
+            "decode_threads": rayon::current_num_threads(),
+            "params": {
+                "datasets": manifest.datasets,
+                "mib": args.mib,
+                "rows": manifest.rows,
+                "cols": manifest.cols,
+                "chunk": manifest.chunk,
+                "deflate_level": manifest.deflate_level,
+                "slab": args.slab,
+                "slabs": args.slabs,
+                "seed": args.seed,
+                "reps": args.reps,
+                "dir": args.dir,
+            },
+            "results": rows,
+        });
+        std::fs::write(out, serde_json::to_string_pretty(&doc).unwrap()).expect("write json");
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn values_are_exact_in_f32() {
+        for k in [0, 7, 63] {
+            for i in [0u64, 1, 4095, 1 << 20, (1 << 24) - 1] {
+                let v = value(k, i);
+                assert_eq!(v, (v as f64) as f32);
+                assert!(v < 32768.0);
+                assert_eq!((v * 256.0).fract(), 0.0);
+            }
+        }
+    }
+
+    /// The h5py script hard-codes this vector to check its splitmix64 port.
+    #[test]
+    fn splitmix64_reference() {
+        let mut s = 42;
+        assert_eq!(splitmix64(&mut s), 0xBDD7_3226_2FEB_6E95);
+    }
+}

crates/clawhdf5-bench/src/bin/consolidation_efficiency.rs

@@ -396,7 +396,7 @@ fn run_memory_reduction_benchmark() {
     println!();
     println!(
         "{:>8}  {:>10}  {:>10}  {:>10}  {:>12}",
-        "Initial", "Remaining", "Eviction%", "Signal OK?", "BM25 Speedup"
+        "Initial", "Remaining", "Eviction%", "Signal OK?", "Records ÷"
     );
     println!("{}", "-".repeat(58));
 
@@ -440,7 +440,8 @@ fn run_memory_reduction_benchmark() {
         // Check all signal records survived
         let signal_survived = signal_ids.iter().all(|&id| engine.get_by_id(id).is_some());
 
-        // Rough speedup: BM25 scales roughly linearly with record count
+        // How many times fewer records there are. Not a measured speedup —
+        // Part 1 measures search latency before and after.
         let speedup = before_count as f64 / after_count.max(1) as f64;
 
         println!(
@@ -480,7 +481,7 @@ fn main() {
     println!("  3. Reducing search latency proportional to record reduction");
     println!();
     println!(
-        "Cycle time scales sub-linearly: 100 records ~microseconds, 100K records ~tens of ms."
+        "Cycle time grows a little faster than linearly: 100 records ~microseconds, 100K records ~tens of ms."
     );
     println!("Signal records with Correction source + high access_count survive eviction.");
 }

crates/clawhdf5-bench/src/bin/footprint_bench.rs

@@ -11,12 +11,14 @@
 //!
 //! Configuration matrix:
 //!   - Text lengths: short (50 chars), medium (200 chars), long (1000 chars)
-//!   - Embedding: 384-dim f32 (1536 bytes raw per record)
+//!   - Embedding: 384-dim, stored as float16 (the default for new stores) or
+//!     f32 with `--f32`; "raw" bytes are counted as f32 input either way
 //!   - WAL: enabled and disabled
 //!
 //! # Usage
 //! ```
-//! cargo run --release --bin footprint_bench
+//! cargo run --release --bin footprint_bench           # float16 stores
+//! cargo run --release --bin footprint_bench -- --f32  # f32 stores
 //! ```
 
 use std::time::Instant;
@@ -24,6 +26,9 @@ use std::time::Instant;
 use clawhdf5_agent::{AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry};
 use tempfile::TempDir;
 
+/// `--f32`: build f32 stores instead of the library's float16 default.
+static F32: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
+
 const EMBEDDING_DIM: usize = 384;
 
 // Raw bytes per record: 384 f32 embeddings + median text + overhead
@@ -152,6 +157,9 @@ fn measure_footprint(
     config.compression = compression;
     config.compression_level = if compression { 6 } else { 0 };
     config.compact_threshold = 0.0;
+    if F32.load(std::sync::atomic::Ordering::Relaxed) {
+        config.float16 = false;
+    }
 
     let mut memory = HDF5Memory::create(config).expect("HDF5Memory::create failed");
 
@@ -241,11 +249,19 @@ fn fmt_n(n: usize) -> String {
 // ---------------------------------------------------------------------------
 
 fn main() {
+    if std::env::args().skip(1).any(|a| a == "--f32") {
+        F32.store(true, std::sync::atomic::Ordering::Relaxed);
+    }
+    let stored = if F32.load(std::sync::atomic::Ordering::Relaxed) {
+        "f32 (1,536 bytes per record)"
+    } else {
+        "float16 (768 bytes per record; the default for new stores)"
+    };
     println!("=================================================================");
     println!("  ClawhDF5 Memory Footprint Benchmark");
     println!("=================================================================");
     println!();
-    println!("Embedding: 384-dim f32 = 1,536 bytes raw per record");
+    println!("Embedding: 384-dim, stored as {stored}; raw input counted as f32");
     println!("Text lengths: short=50 chars, medium=200 chars, long=1000 chars");
     println!();
 

crates/clawhdf5-bench/src/bin/longmemeval_bench.rs

@@ -64,6 +64,11 @@ use tempfile::TempDir;
 
 const EMBEDDING_DIM: usize = 384;
 
+/// `--float16`: build every per-question store with `MemoryConfig::float16`,
+/// so embeddings are rounded to half precision as they are saved — exactly
+/// what such a store searches over.
+static FLOAT16: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
+
 /// A mode's fusion, as one short string for the reports.
 fn describe(mode: Mode) -> String {
     let fusion = match mode.fusion {
@@ -431,6 +436,7 @@ fn evaluate_question(
     let mut config = MemoryConfig::new(dir.path().join("lme.h5"), "lme-bench", EMBEDDING_DIM);
     config.wal_enabled = false;
     config.compact_threshold = 0.0;
+    config.float16 = FLOAT16.load(std::sync::atomic::Ordering::Relaxed);
 
     let mut memory = HDF5Memory::create(config).expect("failed to create HDF5Memory");
     memory.set_token_filter(mode.tokens);
@@ -940,6 +946,10 @@ fn main() {
                 limit = Some(v.parse().expect("--limit must be a positive integer"));
             }
             "--sweep" => sweep = true,
+            "--float16" => {
+                FLOAT16.store(true, std::sync::atomic::Ordering::Relaxed);
+                eprintln!("Stores use MemoryConfig::float16 (half-precision embeddings)");
+            }
             "--rerank-sweep" => {
                 // Re-ranking needs the vector stage to have candidates worth
                 // reordering, so this is an embeddings-only comparison.
@@ -971,6 +981,9 @@ fn main() {
                      --rerank-sweep\n\
                               compare re-ranking off, metadata-only (the old\n\
                               behaviour) and blended at several half-lives.\n\
+                     --float16\n\
+                              build each store with MemoryConfig::float16, to\n\
+                              compare retrieval on half-precision embeddings.\n\
                      --sweep  instead of the three named modes, sweep vector_weight\n\
                               from 0.0 to 1.0 in 0.1 steps. The 0.7/0.3 default was\n\
                               never searched; this is what searches it."

crates/clawhdf5-bench/src/bin/search_harness.rs

@@ -19,6 +19,9 @@
 //! cargo run --release -p clawhdf5-bench --bin search_harness -- --full  # + 100K
 //! cargo run --release -p clawhdf5-bench --bin search_harness -- --json out.json
 //! cargo run --release -p clawhdf5-bench --bin search_harness -- --ann-only --uniform
+//! cargo run --release -p clawhdf5-bench --bin search_harness -- --float16-study --full
+//! cargo run --release -p clawhdf5-bench --bin search_harness -- --options-study --full
+//! cargo run --release -p clawhdf5-bench --bin search_harness -- --signing-study --full
 //! ```
 
 use std::time::{Duration, Instant};
@@ -88,6 +91,9 @@ static UNIFORM: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::n
 /// the memory) instead of f32, to price the recall it costs.
 static INT8: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
 
+/// `--f16-first`: in `--float16-study`, run the float16 store first.
+static F16_FIRST: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
+
 /// `--rerank`: re-score the candidate pool against the exact vectors before
 /// taking the top K.
 static RERANK: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
@@ -230,13 +236,27 @@ struct CountingAllocator;
 
 static LIVE_BYTES: std::sync::atomic::AtomicI64 = std::sync::atomic::AtomicI64::new(0);
 
+/// High-water mark of [`LIVE_BYTES`] since it was last reset.
+///
+/// Live bytes at a checkpoint cannot see a buffer that was allocated and
+/// freed in between, and that is exactly the shape of a transient copy —
+/// which still has to fit in memory while it exists.
+static PEAK_BYTES: std::sync::atomic::AtomicI64 = std::sync::atomic::AtomicI64::new(0);
+
+fn note_peak(live: i64) {
+    PEAK_BYTES.fetch_max(live, std::sync::atomic::Ordering::Relaxed);
+}
+
 // SAFETY: every method forwards to the system allocator with the same layout
 // it was given, and only adds bookkeeping around it.
 unsafe impl std::alloc::GlobalAlloc for CountingAllocator {
     unsafe fn alloc(&self, layout: std::alloc::Layout) -> *mut u8 {
         let ptr = unsafe { std::alloc::System.alloc(layout) };
         if !ptr.is_null() {
-            LIVE_BYTES.fetch_add(layout.size() as i64, std::sync::atomic::Ordering::Relaxed);
+            let live = LIVE_BYTES
+                .fetch_add(layout.size() as i64, std::sync::atomic::Ordering::Relaxed)
+                + layout.size() as i64;
+            note_peak(live);
         }
         ptr
     }
@@ -249,10 +269,9 @@ unsafe impl std::alloc::GlobalAlloc for CountingAllocator {
     unsafe fn realloc(&self, ptr: *mut u8, layout: std::alloc::Layout, new_size: usize) -> *mut u8 {
         let new_ptr = unsafe { std::alloc::System.realloc(ptr, layout, new_size) };
         if !new_ptr.is_null() {
-            LIVE_BYTES.fetch_add(
-                new_size as i64 - layout.size() as i64,
-                std::sync::atomic::Ordering::Relaxed,
-            );
+            let delta = new_size as i64 - layout.size() as i64;
+            let live = LIVE_BYTES.fetch_add(delta, std::sync::atomic::Ordering::Relaxed) + delta;
+            note_peak(live);
         }
         new_ptr
     }
@@ -266,6 +285,19 @@ fn heap_bytes() -> u64 {
     LIVE_BYTES.load(std::sync::atomic::Ordering::Relaxed).max(0) as u64
 }
 
+/// Start watching for a new high-water mark from the current live total.
+fn reset_peak() {
+    PEAK_BYTES.store(
+        LIVE_BYTES.load(std::sync::atomic::Ordering::Relaxed),
+        std::sync::atomic::Ordering::Relaxed,
+    );
+}
+
+/// The highest live total seen since [`reset_peak`].
+fn peak_bytes() -> u64 {
+    PEAK_BYTES.load(std::sync::atomic::Ordering::Relaxed).max(0) as u64
+}
+
 fn mib(bytes: u64) -> f64 {
     bytes as f64 / (1 << 20) as f64
 }
@@ -457,6 +489,394 @@ fn bench_end_to_end(n: usize, json: &mut Vec<serde_json::Value>) {
     }));
 }
 
+// ---------------------------------------------------------------------------
+// Signing study: what does an Ed25519-signed checkpoint cost?
+// ---------------------------------------------------------------------------
+
+/// `--signing-study`: checkpoint time unsigned vs signed, `verify` time, and
+/// the file-size cost of the stored per-record hashes. Default store
+/// settings (float16, int8 index). Medians of five checkpoints / three
+/// verifies.
+fn signing_study(n: usize) {
+    use clawhdf5_agent::signing::SigningKey;
+    let data = make_dataset(n, 0x516 ^ n as u64);
+    let mut rng = Rng(9);
+    let entries: Vec<MemoryEntry> = data
+        .vectors
+        .iter()
+        .enumerate()
+        .map(|(i, v)| MemoryEntry {
+            chunk: text_for(data.cluster_of[i], i, &mut rng),
+            embedding: v.clone(),
+            source_channel: "bench".into(),
+            timestamp: i as f64,
+            session_id: format!("s{}", i % 50),
+            tags: format!("t{i}"),
+        })
+        .collect();
+    let dir = tempfile::tempdir().unwrap();
+    let path = dir.path().join("sign.h5");
+    let mut mem = HDF5Memory::create(MemoryConfig::new(path.clone(), "bench", DIM)).unwrap();
+    mem.save_batch(entries).unwrap();
+    std::hint::black_box(mem.hybrid_search(&data.queries[0], "", 1.0, 0.0, K));
+
+    let median = |mut v: Vec<Duration>| {
+        v.sort();
+        v[v.len() / 2]
+    };
+    let checkpoint = |mem: &mut HDF5Memory| {
+        median(
+            (0..5)
+                .map(|_| {
+                    let t = Instant::now();
+                    mem.flush_wal().unwrap();
+                    t.elapsed()
+                })
+                .collect(),
+        )
+    };
+    let unsigned = checkpoint(&mut mem);
+    let unsigned_bytes = std::fs::metadata(&path).unwrap().len();
+    let key = SigningKey::from_bytes(&[7; 32]);
+    mem.set_signing_key(key.clone());
+    let signed = checkpoint(&mut mem);
+    let signed_bytes = std::fs::metadata(&path).unwrap().len();
+    drop(mem);
+    let vk = key.verifying_key();
+    let verify = median(
+        (0..3)
+            .map(|_| {
+                let t = Instant::now();
+                let r = HDF5Memory::verify(&path, &vk).unwrap();
+                let d = t.elapsed();
+                assert!(r.is_valid());
+                d
+            })
+            .collect(),
+    );
+    println!(
+        "| {n} | {:.1} | {:.1} | {:+.1} | {:.1} | {:+.2} |",
+        millis(unsigned),
+        millis(signed),
+        millis(signed) - millis(unsigned),
+        millis(verify),
+        (signed_bytes as f64 - unsigned_bytes as f64) / (1024.0 * 1024.0),
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Search options study: source filters, re-ranking, confidence rejection
+// ---------------------------------------------------------------------------
+
+/// `--options-study`: what `HDF5Memory::search`'s options cost and whether a
+/// filtered search finds the right records. Filters keep 50%, 10% or 1% of
+/// the store at random, or two whole clusters away from the query (the case
+/// the index cannot serve, which falls back to an exact scan). Recall is
+/// vector-only against an exact scan of the allowed records; latency is full
+/// hybrid search. Hebbian boosting is off.
+fn options_study(n: usize) {
+    use clawhdf5_agent::SearchOptions;
+    use clawhdf5_agent::confidence::ConfidenceConfig;
+    use clawhdf5_agent::hybrid::Fusion;
+    use clawhdf5_agent::reranker::ReRankConfig;
+
+    let data = make_dataset(n, 0x0B7 ^ n as u64);
+    let n_clusters = data.cluster_of.iter().max().map_or(1, |m| m + 1);
+    let mut rng = Rng(5);
+    let bucket_of: Vec<usize> = (0..n).map(|_| rng.below(100)).collect();
+    let bucket = &bucket_of;
+    let query_texts: Vec<String> = data
+        .query_cluster
+        .iter()
+        .enumerate()
+        .map(|(i, c)| text_for(*c, i, &mut rng))
+        .collect();
+    let exact_top = |q: &[f32], allowed: &dyn Fn(usize) -> bool| -> Vec<usize> {
+        let mut s: Vec<(usize, f32)> = (0..n)
+            .filter(|&i| allowed(i))
+            .map(|i| (i, data.vectors[i].iter().zip(q).map(|(a, b)| a * b).sum()))
+            .collect();
+        s.sort_by(|a, b| b.1.total_cmp(&a.1).then(a.0.cmp(&b.0)));
+        s.into_iter().take(K).map(|(i, _)| i).collect()
+    };
+
+    // Two stores: channel = random bucket, and channel = cluster.
+    let dir = tempfile::tempdir().unwrap();
+    let mut stores = Vec::new();
+    for by_cluster in [false, true] {
+        let mut rng = Rng(3);
+        let entries: Vec<MemoryEntry> = data
+            .vectors
+            .iter()
+            .enumerate()
+            .map(|(i, v)| MemoryEntry {
+                chunk: text_for(data.cluster_of[i], i, &mut rng),
+                embedding: v.clone(),
+                source_channel: if by_cluster {
+                    format!("c{}", data.cluster_of[i])
+                } else {
+                    format!("b{}", bucket[i])
+                },
+                timestamp: i as f64,
+                session_id: format!("s{}", i % 50),
+                tags: format!("t{i}"),
+            })
+            .collect();
+        let mut config = MemoryConfig::new(
+            dir.path().join(format!("opt_{by_cluster}.h5")),
+            "bench",
+            DIM,
+        );
+        config.hebbian_boost = 0.0;
+        let mut mem = HDF5Memory::create(config).unwrap();
+        mem.save_batch(entries).unwrap();
+        std::hint::black_box(mem.search(&data.queries[0], "", &SearchOptions::new(K)));
+        stores.push(mem);
+    }
+
+    let vector_only = SearchOptions::new(K).with_fusion(Fusion::Weighted {
+        vector: 1.0,
+        keyword: 0.0,
+    });
+    // (label, store, channels for query i, allowed(i, record))
+    type Case<'a> = (
+        String,
+        usize,
+        Box<dyn Fn(usize) -> Option<Vec<String>> + 'a>,
+        Box<dyn Fn(usize, usize) -> bool + 'a>,
+    );
+    let mut cases: Vec<Case> = vec![(
+        "no filter".into(),
+        0,
+        Box::new(|_| None),
+        Box::new(|_, _| true),
+    )];
+    for pct in [50usize, 10, 1] {
+        cases.push((
+            format!("random {pct}%"),
+            0,
+            Box::new(move |_| Some((0..pct).map(|b| format!("b{b}")).collect())),
+            Box::new(move |_, i| bucket[i] < pct),
+        ));
+    }
+    let d = &data;
+    let away = move |qi: usize| {
+        let qc = d.query_cluster[qi];
+        [
+            (qc + n_clusters / 3) % n_clusters,
+            (qc + 2 * n_clusters / 3) % n_clusters,
+        ]
+    };
+    cases.push((
+        "2 clusters away from the query".into(),
+        1,
+        Box::new(move |qi| Some(away(qi).iter().map(|c| format!("c{c}")).collect())),
+        Box::new(move |qi, i| away(qi).contains(&d.cluster_of[i])),
+    ));
+
+    for (label, store, channels, allowed) in &cases {
+        let mem = &mut stores[*store];
+        let mut hits = 0;
+        let mut kept = 0;
+        for (qi, q) in data.queries.iter().enumerate() {
+            let mut opts = vector_only.clone();
+            opts.source_channels = channels(qi);
+            let got = mem.search(q, "", &opts);
+            let want = exact_top(q, &|i| allowed(qi, i));
+            kept += want.len();
+            hits += got.iter().filter(|r| want.contains(&r.index)).count();
+        }
+        let latency = summarize(
+            (0..N_QUERIES)
+                .map(|qi| {
+                    let mut opts = SearchOptions::new(K);
+                    opts.source_channels = channels(qi);
+                    let t = Instant::now();
+                    std::hint::black_box(mem.search(&data.queries[qi], &query_texts[qi], &opts));
+                    t.elapsed()
+                })
+                .collect(),
+        );
+        println!(
+            "| {n} | {label} | {:.4} | {:.3} | {:.3} |",
+            hits as f64 / kept.max(1) as f64,
+            millis(latency.p50),
+            millis(latency.p99),
+        );
+    }
+
+    let mem = &mut stores[0];
+    for (label, opts) in [
+        (
+            "re-rank",
+            SearchOptions::new(K).with_rerank(ReRankConfig::default()),
+        ),
+        (
+            "re-rank + confidence",
+            SearchOptions::new(K)
+                .with_rerank(ReRankConfig::default())
+                .with_confidence(ConfidenceConfig::default()),
+        ),
+    ] {
+        let latency = summarize(
+            (0..N_QUERIES)
+                .map(|qi| {
+                    let t = Instant::now();
+                    std::hint::black_box(mem.search(&data.queries[qi], &query_texts[qi], &opts));
+                    t.elapsed()
+                })
+                .collect(),
+        );
+        println!(
+            "| {n} | {label} | — | {:.3} | {:.3} |",
+            millis(latency.p50),
+            millis(latency.p99)
+        );
+    }
+}
+
+// ---------------------------------------------------------------------------
+// float16 study: what does half-precision embedding storage cost?
+// ---------------------------------------------------------------------------
+
+/// `--float16-study`: the same data in an `f32` store and a `float16` store.
+/// Reports file size, checkpoint and open time, vector-search recall@10
+/// against an exact scan of the *original* f32 vectors, how often the two
+/// stores return the same top 10, and `hybrid_search` latency. Hebbian
+/// boosting is off, so every query sees the same store.
+fn float16_study(n: usize) {
+    let data = make_dataset(n, 0xF16 ^ n as u64);
+    let mut rng = Rng(11);
+    let query_texts: Vec<String> = data
+        .query_cluster
+        .iter()
+        .enumerate()
+        .map(|(i, c)| text_for(*c, i, &mut rng))
+        .collect();
+
+    // Exact top K by cosine (the vectors are unit length) on the f32 inputs.
+    let exact: Vec<Vec<usize>> = data
+        .queries
+        .iter()
+        .map(|q| {
+            let mut scored: Vec<(usize, f32)> = data
+                .vectors
+                .iter()
+                .enumerate()
+                .map(|(i, v)| (i, v.iter().zip(q).map(|(a, b)| a * b).sum()))
+                .collect();
+            scored.sort_by(|a, b| b.1.total_cmp(&a.1).then(a.0.cmp(&b.0)));
+            scored.into_iter().take(K).map(|(i, _)| i).collect()
+        })
+        .collect();
+
+    let dir = tempfile::tempdir().unwrap();
+    let mut per_variant: Vec<(bool, Vec<Vec<usize>>)> = Vec::new();
+    // `--f16-first` swaps the order, to check the numbers do not depend on
+    // which store runs first (page cache, allocator, CPU frequency).
+    let order = if F16_FIRST.load(std::sync::atomic::Ordering::Relaxed) {
+        [true, false]
+    } else {
+        [false, true]
+    };
+    for float16 in order {
+        let path = dir.path().join(format!("f16study_{float16}.h5"));
+        let mut rng = Rng(3);
+        let entries: Vec<MemoryEntry> = data
+            .vectors
+            .iter()
+            .enumerate()
+            .map(|(i, v)| MemoryEntry {
+                chunk: text_for(data.cluster_of[i], i, &mut rng),
+                embedding: v.clone(),
+                source_channel: "bench".into(),
+                timestamp: i as f64,
+                session_id: format!("s{}", i % 50),
+                tags: format!("t{i}"),
+            })
+            .collect();
+        let mut config = MemoryConfig::new(path.clone(), "bench", DIM);
+        config.float16 = float16;
+        config.hebbian_boost = 0.0;
+        let mut mem = HDF5Memory::create(config).unwrap();
+        mem.save_batch(entries).unwrap();
+        // Build the indexes, then time a checkpoint that writes everything.
+        std::hint::black_box(mem.hybrid_search(&data.queries[0], "", 1.0, 0.0, K));
+        let t = Instant::now();
+        mem.flush_wal().unwrap();
+        let checkpoint = t.elapsed();
+        drop(mem);
+        let file_bytes = std::fs::metadata(&path).unwrap().len();
+
+        // Median of three opens.
+        let mut opens: Vec<Duration> = (0..3)
+            .map(|_| {
+                let t = Instant::now();
+                let m = HDF5Memory::open(&path).unwrap();
+                let d = t.elapsed();
+                drop(m);
+                d
+            })
+            .collect();
+        opens.sort();
+        let mut mem = HDF5Memory::open(&path).unwrap();
+
+        // Vector-only search: empty text, all weight on the vector stage.
+        let results: Vec<Vec<usize>> = data
+            .queries
+            .iter()
+            .map(|q| {
+                mem.hybrid_search(q, "", 1.0, 0.0, K)
+                    .iter()
+                    .map(|r| r.index)
+                    .collect()
+            })
+            .collect();
+        let hits: usize = results
+            .iter()
+            .zip(&exact)
+            .map(|(got, want)| got.iter().filter(|i| want.contains(i)).count())
+            .sum();
+        let recall = hits as f64 / (K * data.queries.len()) as f64;
+
+        let latency = summarize(
+            (0..N_QUERIES)
+                .map(|i| {
+                    let t = Instant::now();
+                    std::hint::black_box(mem.hybrid_search(
+                        &data.queries[i],
+                        &query_texts[i],
+                        0.4,
+                        0.6,
+                        K,
+                    ));
+                    t.elapsed()
+                })
+                .collect(),
+        );
+        let overlap = match per_variant.first() {
+            Some((_, other)) => {
+                let same: usize = results
+                    .iter()
+                    .zip(other)
+                    .map(|(a, b)| a.iter().filter(|i| b.contains(i)).count())
+                    .sum();
+                format!("{:.4}", same as f64 / (K * data.queries.len()) as f64)
+            }
+            None => "—".into(),
+        };
+        println!(
+            "| {n} | {} | {:.1} | {:.0} | {:.1} | {recall:.4} | {overlap} | {:.3} |",
+            if float16 { "float16" } else { "f32" },
+            mib(file_bytes),
+            millis(checkpoint),
+            millis(opens[1]),
+            millis(latency.p50),
+        );
+        per_variant.push((float16, results));
+    }
+}
+
 // ---------------------------------------------------------------------------
 // Fusion study: does capping the keyword candidate pool change the ranking?
 // ---------------------------------------------------------------------------
@@ -580,19 +1000,24 @@ fn bench_footprint(n: usize) {
     let path = mem.config().path.clone();
     drop(mem);
     let before_open = heap_bytes();
+    reset_peak();
     let reopened = HDF5Memory::open(&path).unwrap();
     let after_open = heap_bytes();
     let loaded = after_open.saturating_sub(before_open);
+    // Peak over the open, not just what it leaves behind: a buffer allocated
+    // and freed during the parse never shows up in the live total.
+    let peak = peak_bytes().saturating_sub(before_open);
     drop(reopened);
 
     let raw = (n * DIM * 4) as u64;
     println!(
-        "| {n} | {:.0} | {:.0} | {:.0} | {:.0} | {:.0} | {:.2}x |",
+        "| {n} | {:.0} | {:.0} | {:.0} | {:.0} | {:.0} | {:.0} | {:.2}x |",
         mib(raw),
         mib(after_entries.saturating_sub(base)),
         mib(after_store.saturating_sub(after_entries)),
         mib(after_indexes.saturating_sub(after_store)),
         mib(loaded),
+        mib(peak),
         loaded as f64 / raw as f64,
     );
 }
@@ -611,6 +1036,52 @@ fn main() {
         }
         return;
     }
+    if args.iter().any(|a| a == "--signing-study") {
+        println!("## Signed checkpoints ({DIM}-dim, float16, int8 index)\n");
+        println!(
+            "| N | checkpoint ms, unsigned | checkpoint ms, signed | signing adds ms | verify ms | file MiB added |"
+        );
+        println!("|---:|---:|---:|---:|---:|---:|");
+        for &n in if full {
+            &[1_000, 10_000, 100_000][..]
+        } else {
+            &[1_000, 10_000][..]
+        } {
+            signing_study(n);
+        }
+        return;
+    }
+    if args.iter().any(|a| a == "--options-study") {
+        println!("## Search options ({DIM}-dim, k = {K}, Hebbian boost off)\n");
+        println!("| N | options | filtered recall@10 | p50 ms | p99 ms |");
+        println!("|---:|---|---:|---:|---:|");
+        for &n in if full {
+            &[10_000, 100_000][..]
+        } else {
+            &[10_000][..]
+        } {
+            options_study(n);
+        }
+        return;
+    }
+    if args.iter().any(|a| a == "--f16-first") {
+        F16_FIRST.store(true, std::sync::atomic::Ordering::Relaxed);
+    }
+    if args.iter().any(|a| a == "--float16-study") {
+        println!("## float16 embedding storage ({DIM}-dim, int8 index, Hebbian boost off)\n");
+        println!(
+            "| N | embeddings | file MiB | checkpoint ms | open ms | recall@10 | top-10 overlap with the other | hybrid p50 ms |"
+        );
+        println!("|---:|---|---:|---:|---:|---:|---:|---:|");
+        for &n in if full {
+            &[1_000, 10_000, 100_000][..]
+        } else {
+            &[1_000, 10_000][..]
+        } {
+            float16_study(n);
+        }
+        return;
+    }
     if args.iter().any(|a| a == "--int8") {
         INT8.store(true, std::sync::atomic::Ordering::Relaxed);
         println!("(int8-quantised index vectors)");
@@ -644,9 +1115,9 @@ fn main() {
     if args.iter().any(|a| a == "--footprint") {
         println!("\n### Resident memory, {DIM}-dim f32\n");
         println!(
-            "| N | vectors (raw) | entries MiB | store MiB | indexes MiB | reopened MiB | reopened / raw |"
+            "| N | vectors (raw) | entries MiB | store MiB | indexes MiB | reopened MiB | peak during open MiB | reopened / raw |"
         );
-        println!("|---:|---:|---:|---:|---:|---:|---:|");
+        println!("|---:|---:|---:|---:|---:|---:|---:|---:|");
         for &n in sizes {
             bench_footprint(n);
         }

crates/clawhdf5-bench/tests/concurrent_read_smoke.rs

@@ -0,0 +1,148 @@
+//! Keeps the concurrent-read harnesses working: runs `concurrent_read`, the
+//! h5py script (threads and processes) and the comparison script end to end
+//! on tiny files. h5py reading the files also checks, element by element at
+//! spot positions, that both harnesses generate the same data and slabs.
+//!
+//! The h5py half is skipped when python3 with h5py is unavailable, unless
+//! `CLAWHDF5_REQUIRE_INTEROP=1`; `CLAWHDF5_PYTHON` picks the interpreter.
+
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+fn python() -> String {
+    std::env::var("CLAWHDF5_PYTHON").unwrap_or_else(|_| "python3".to_string())
+}
+
+fn interop_required() -> bool {
+    std::env::var("CLAWHDF5_REQUIRE_INTEROP").is_ok_and(|v| v == "1")
+}
+
+fn python_available() -> bool {
+    Command::new(python())
+        .args(["-c", "import h5py, numpy"])
+        .output()
+        .map(|o| o.status.success())
+        .unwrap_or(false)
+}
+
+fn scripts() -> PathBuf {
+    Path::new(env!("CARGO_MANIFEST_DIR")).join("scripts")
+}
+
+fn run(cmd: &mut Command) -> String {
+    let out = cmd.output().expect("spawn");
+    assert!(
+        out.status.success(),
+        "{cmd:?} failed\nSTDOUT:\n{}\nSTDERR:\n{}",
+        String::from_utf8_lossy(&out.stdout),
+        String::from_utf8_lossy(&out.stderr)
+    );
+    String::from_utf8_lossy(&out.stdout).into_owned()
+}
+
+const SMALL: [&str; 8] = [
+    "--threads",
+    "1,2",
+    "--slabs",
+    "8",
+    "--reps",
+    "1",
+    "--slab",
+    "64",
+];
+
+fn results(path: &Path) -> serde_json::Value {
+    serde_json::from_str(&std::fs::read_to_string(path).unwrap()).unwrap()
+}
+
+#[test]
+fn harnesses_run_end_to_end_on_tiny_files() {
+    let dir = tempfile::TempDir::new().unwrap();
+    let data = dir.path().join("data");
+    let claw = dir.path().join("claw.json");
+
+    let bin = env!("CARGO_BIN_EXE_concurrent_read");
+    run(Command::new(bin)
+        .arg("--dir")
+        .arg(&data)
+        .args(["--datasets", "3", "--mib", "1"])
+        .args(SMALL)
+        .arg("--json")
+        .arg(&claw));
+    // Second run reuses the files (and exercises --cold).
+    let out = Command::new(bin)
+        .arg("--dir")
+        .arg(&data)
+        .args(["--datasets", "3", "--mib", "1", "--cold"])
+        .args(SMALL)
+        .output()
+        .unwrap();
+    assert!(out.status.success());
+    assert!(String::from_utf8_lossy(&out.stderr).contains("reusing"));
+
+    let doc = results(&claw);
+    assert_eq!(doc["tool"], "clawhdf5");
+    // 2 layouts x 2 modes x 2 thread counts.
+    assert_eq!(doc["results"].as_array().unwrap().len(), 8);
+    for r in doc["results"].as_array().unwrap() {
+        assert!(r["mb_s"].as_f64().unwrap() > 0.0, "{r}");
+    }
+
+    if !python_available() {
+        assert!(
+            !interop_required(),
+            "CLAWHDF5_REQUIRE_INTEROP=1 but {} has no h5py",
+            python()
+        );
+        eprintln!("skipping the h5py half: no h5py in {}", python());
+        return;
+    }
+    let mut jsons = vec![claw];
+    for executor in ["threads", "processes"] {
+        let out = dir.path().join(format!("h5py-{executor}.json"));
+        run(Command::new(python())
+            .arg(scripts().join("concurrent_read_h5py.py"))
+            .arg("--dir")
+            .arg(&data)
+            .args(["--executor", executor])
+            .args(SMALL)
+            .arg("--json")
+            .arg(&out));
+        let doc = results(&out);
+        assert_eq!(doc["tool"], format!("h5py-{executor}"));
+        assert_eq!(doc["results"].as_array().unwrap().len(), 8);
+        jsons.push(out);
+    }
+    let table = run(Command::new(python())
+        .arg(scripts().join("compare_concurrent_read.py"))
+        .args(&jsons));
+    assert!(table.contains("| deflate | same | 2 |"), "{table}");
+    assert!(table.contains("clawhdf5 / h5py-processes"), "{table}");
+
+    // A different workload must not be compared.
+    let other = dir.path().join("other.json");
+    run(Command::new(python())
+        .arg(scripts().join("concurrent_read_h5py.py"))
+        .arg("--dir")
+        .arg(&data)
+        .args([
+            "--threads",
+            "1",
+            "--slabs",
+            "4",
+            "--reps",
+            "1",
+            "--slab",
+            "64",
+        ])
+        .arg("--json")
+        .arg(&other));
+    let out = Command::new(python())
+        .arg(scripts().join("compare_concurrent_read.py"))
+        .arg(&jsons[0])
+        .arg(&other)
+        .output()
+        .unwrap();
+    assert!(!out.status.success());
+    assert!(String::from_utf8_lossy(&out.stderr).contains("slabs"));
+}

crates/clawhdf5-cli/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-cli"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 license = "MIT"
 description = "CLI for clawhdf5 agent memory — create, save, search, recall, stats"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
@@ -14,7 +15,7 @@ name = "clawhdf5"
 path = "src/main.rs"
 
 [dependencies]
-clawhdf5-agent = { path = "../clawhdf5-agent", version = "2.6.0" }
+clawhdf5-agent = { path = "../clawhdf5-agent", version = "2.7.0" }
 clap = { version = "4", features = ["derive", "env"] }
 serde_json = "1"
 serde = { workspace = true }

crates/clawhdf5-cli/src/main.rs

@@ -1,15 +1,22 @@
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 use clap::{Parser, Subcommand};
+use clawhdf5_agent::signing::{self, SigningKey, VerifyingKey};
 use clawhdf5_agent::{AgentMemory, HDF5Memory, MemoryConfig, MemoryEntry};
 
 /// ClawhDF5 — HDF5-backed cognitive memory for AI agents
 #[derive(Parser)]
 #[command(name = "clawhdf5", version, about)]
 struct Cli {
-    /// Path to the .h5 memory file
+    /// Path to the .h5 memory file (not needed for `keygen`)
     #[arg(short, long, env = "CLAWHDF5_PATH")]
-    path: PathBuf,
+    path: Option<PathBuf>,
+
+    /// File holding an Ed25519 signing key (64 hex characters, from
+    /// `keygen`). Every checkpoint this command makes is then signed; a
+    /// signed store refuses to checkpoint without it.
+    #[arg(long, env = "CLAWHDF5_SIGNING_KEY", global = true)]
+    signing_key: Option<PathBuf>,
 
     #[command(subcommand)]
     command: Commands,
@@ -28,10 +35,22 @@ enum Commands {
         /// Enable write-ahead log
         #[arg(long)]
         wal: bool,
-        /// Store the vector index's copy of the embeddings as int8, roughly
-        /// halving a loaded store's memory at about 13% fewer queries/second
+        /// Hold the vector index's copy of the embeddings as f32 instead of
+        /// the default int8 (which uses a quarter of the memory and is faster
+        /// at equal recall)
         #[arg(long)]
+        f32_index: bool,
+        /// Accepted for compatibility; int8 is now the default
+        #[arg(long, hide = true, conflicts_with = "f32_index")]
         quantized_index: bool,
+        /// Store embeddings as full-precision f32 instead of the default
+        /// half precision (float16: half the bytes, about three significant
+        /// digits, values within ±65504)
+        #[arg(long)]
+        f32: bool,
+        /// Accepted for compatibility; float16 is now the default
+        #[arg(long, hide = true, conflicts_with = "f32")]
+        float16: bool,
     },
     /// Save a memory entry (reads JSON from stdin or --json)
     Save {
@@ -79,6 +98,38 @@ enum Commands {
         /// Destination path
         dest: PathBuf,
     },
+    /// Generate an Ed25519 signing key for signed checkpoints
+    Keygen {
+        /// Where to write the secret key (created new, owner-only on Unix)
+        #[arg(long)]
+        out: PathBuf,
+    },
+    /// Verify a signed store against a public key; exit status 2 if not valid
+    Verify {
+        /// The trusted public key: 64 hex characters, or a file holding them
+        #[arg(long)]
+        public_key: String,
+    },
+}
+
+fn read_signing_key(path: &Path) -> Result<SigningKey, Box<dyn std::error::Error>> {
+    let text = std::fs::read_to_string(path)
+        .map_err(|e| format!("cannot read signing key {}: {e}", path.display()))?;
+    let bytes = signing::from_hex::<32>(&text)
+        .ok_or_else(|| format!("{} is not a 64-hex-character key", path.display()))?;
+    Ok(SigningKey::from_bytes(&bytes))
+}
+
+/// Open for writing, with the signing key applied if one was given.
+fn open_writable(
+    path: &Path,
+    key: &Option<SigningKey>,
+) -> Result<HDF5Memory, Box<dyn std::error::Error>> {
+    let mut mem = HDF5Memory::open(path)?;
+    if let Some(k) = key {
+        mem.set_signing_key(k.clone());
+    }
+    Ok(mem)
 }
 
 fn main() {
@@ -91,24 +142,76 @@ fn main() {
 }
 
 fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
+    if let Commands::Keygen { out } = &cli.command {
+        let key = signing::generate_key();
+        let mut opts = std::fs::OpenOptions::new();
+        opts.write(true).create_new(true);
+        #[cfg(unix)]
+        {
+            use std::os::unix::fs::OpenOptionsExt;
+            opts.mode(0o600);
+        }
+        use std::io::Write;
+        let mut f = opts
+            .open(out)
+            .map_err(|e| format!("cannot create {}: {e}", out.display()))?;
+        writeln!(f, "{}", signing::to_hex(&key.to_bytes()))?;
+        let j = serde_json::json!({
+            "status": "generated",
+            "secret_key_file": out.display().to_string(),
+            "public_key": signing::to_hex(&key.verifying_key().to_bytes()),
+        });
+        println!("{}", serde_json::to_string_pretty(&j)?);
+        return Ok(());
+    }
+    let path = cli
+        .path
+        .clone()
+        .ok_or("--path (or CLAWHDF5_PATH) is required")?;
+    let key = cli
+        .signing_key
+        .as_deref()
+        .map(read_signing_key)
+        .transpose()?;
     match cli.command {
         Commands::Create {
             agent_id,
             dim,
             wal,
-            quantized_index,
+            f32_index,
+            quantized_index: _,
+            f32,
+            float16: _,
         } => {
-            let mut config = MemoryConfig::new(cli.path.clone(), &agent_id, dim);
+            let mut config = MemoryConfig::new(path.clone(), &agent_id, dim);
             config.wal_enabled = wal;
-            config.quantized_index = quantized_index;
-            let mem = HDF5Memory::create(config)?;
+            // As with --f32-index: only ever switch the library default off.
+            if f32 {
+                config.float16 = false;
+            }
+            let config_float16 = config.float16;
+            // Only ever switch *off* the library default: assigning the flag
+            // outright would force every CLI-created store back to f32 unless
+            // the caller knew to ask for int8.
+            if f32_index {
+                config.quantized_index = false;
+            }
+            let config_quantized = config.quantized_index;
+            let mut mem = HDF5Memory::create(config)?;
+            // Sign straight away, so the store is never on disk unsigned.
+            if let Some(k) = &key {
+                mem.set_signing_key(k.clone());
+                mem.flush_wal()?;
+            }
             let j = serde_json::json!({
                 "status": "created",
-                "path": cli.path.display().to_string(),
+                "path": path.display().to_string(),
                 "agent_id": agent_id,
                 "embedding_dim": dim,
                 "wal_enabled": wal,
-                "quantized_index": quantized_index,
+                "quantized_index": config_quantized,
+                "float16": config_float16,
+                "signed": mem.is_signed(),
                 "count": mem.count(),
             });
             println!("{}", serde_json::to_string_pretty(&j)?);
@@ -125,7 +228,7 @@ fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
                 }
             };
             let entry: MemoryEntry = serde_json::from_str(&input)?;
-            let mut mem = HDF5Memory::open(&cli.path)?;
+            let mut mem = open_writable(&path, &key)?;
             let idx = mem.save(entry)?;
             let j = serde_json::json!({ "status": "saved", "index": idx, "count": mem.count() });
             println!("{}", serde_json::to_string(&j)?);
@@ -139,7 +242,7 @@ fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
             keyword_weight,
         } => {
             let emb: Vec<f32> = serde_json::from_str(&embedding)?;
-            let mut mem = HDF5Memory::open(&cli.path)?;
+            let mut mem = open_writable(&path, &key)?;
             let results = mem.hybrid_search(&emb, &query, vector_weight, keyword_weight, top_k);
             let j: Vec<serde_json::Value> = results
                 .iter()
@@ -157,7 +260,7 @@ fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
         }
 
         Commands::Recall { index } => {
-            let mem = HDF5Memory::open_read_only(&cli.path)?;
+            let mem = HDF5Memory::open_read_only(&path)?;
             match mem.get_chunk(index) {
                 Some(content) => {
                     let j = serde_json::json!({ "index": index, "chunk": content });
@@ -171,22 +274,23 @@ fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
         }
 
         Commands::Stats => {
-            let mem = HDF5Memory::open_read_only(&cli.path)?;
+            let mem = HDF5Memory::open_read_only(&path)?;
             let cfg = mem.config();
             let j = serde_json::json!({
-                "path": cli.path.display().to_string(),
+                "path": path.display().to_string(),
                 "agent_id": cfg.agent_id,
                 "embedding_dim": cfg.embedding_dim,
                 "count": mem.count(),
                 "active": mem.count_active(),
                 "wal_enabled": cfg.wal_enabled,
                 "wal_pending": mem.wal_pending_count(),
+                "signed": mem.is_signed(),
             });
             println!("{}", serde_json::to_string_pretty(&j)?);
         }
 
         Commands::FlushWal => {
-            let mut mem = HDF5Memory::open(&cli.path)?;
+            let mut mem = open_writable(&path, &key)?;
             let before = mem.wal_pending_count();
             mem.flush_wal()?;
             let j = serde_json::json!({
@@ -198,7 +302,7 @@ fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
         }
 
         Commands::AgentsMd { output } => {
-            let mem = HDF5Memory::open_read_only(&cli.path)?;
+            let mem = HDF5Memory::open_read_only(&path)?;
             let md = mem.generate_agents_md();
             match output {
                 Some(p) => {
@@ -210,7 +314,7 @@ fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
         }
 
         Commands::Export => {
-            let mem = HDF5Memory::open_read_only(&cli.path)?;
+            let mem = HDF5Memory::open_read_only(&path)?;
             for i in 0..mem.count() {
                 if let Some(chunk) = mem.get_chunk(i) {
                     let j = serde_json::json!({ "index": i, "chunk": chunk });
@@ -219,11 +323,44 @@ fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
             }
         }
 
+        Commands::Keygen { .. } => unreachable!("handled before opening a store"),
+
+        Commands::Verify { public_key } => {
+            let text = if Path::new(&public_key).is_file() {
+                std::fs::read_to_string(&public_key)?
+            } else {
+                public_key
+            };
+            let bytes = signing::from_hex::<32>(&text)
+                .ok_or("--public-key must be 64 hex characters or a file holding them")?;
+            let trusted = VerifyingKey::from_bytes(&bytes)?;
+            let r = HDF5Memory::verify(&path, &trusted)?;
+            let j = serde_json::json!({
+                "valid": r.is_valid(),
+                "signed": r.signed,
+                "key_matches": r.key_matches,
+                "signature_valid": r.signature_valid,
+                "records_match": r.records_match,
+                "settings_match": r.settings_match,
+                "sessions_match": r.sessions_match,
+                "graph_match": r.graph_match,
+                "changed_records": r.changed_records,
+                "record_count": r.record_count,
+                "signed_record_count": r.signed_record_count,
+                "signed_by": r.public_key.map(|k| signing::to_hex(&k)),
+                "wal_entries_unsigned": r.wal_entries_unsigned,
+            });
+            println!("{}", serde_json::to_string_pretty(&j)?);
+            if !r.is_valid() {
+                std::process::exit(2);
+            }
+        }
+
         Commands::Snapshot { dest } => {
-            let _result = clawhdf5_agent::storage::snapshot_file(&cli.path, &dest)?;
+            let _result = clawhdf5_agent::storage::snapshot_file(&path, &dest)?;
             let j = serde_json::json!({
                 "status": "snapshot_created",
-                "source": cli.path.display().to_string(),
+                "source": path.display().to_string(),
                 "dest": dest.display().to_string(),
             });
             println!("{}", serde_json::to_string(&j)?);

crates/clawhdf5-derive/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-derive"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "Derive macros for rustyhdf5 HDF5 traits"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"

crates/clawhdf5-filters/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-filters"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "Filter and compression pipeline for clawhdf5"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
@@ -25,8 +26,12 @@ name = "compression_bench"
 harness = false
 
 [features]
-default = ["fast-deflate"]
+# Pure-Rust zlib-rs by default; `fast-deflate` (zlib-ng, C) overrides it.
+default = ["zlib-rs"]
 fast-deflate = ["flate2/zlib-ng"]
 system-zlib = ["flate2/zlib-default"]
-zlib-rs = ["flate2/zlib-rs"]
+# `runtime_detection` gives zlib-rs `std`, which it needs to detect and use
+# SIMD at runtime. flate2 enables it by default, but we build flate2 with
+# default-features = false, and without it zlib-rs inflates 3.5x slower.
+zlib-rs = ["flate2/zlib-rs", "flate2/runtime_detection"]
 apple-compression = []

crates/clawhdf5-filters/README.md

@@ -8,16 +8,18 @@ Filter and compression pipeline for clawhdf5.
 ## Features
 
 - DEFLATE compression/decompression
-- Fast deflate via zlib-ng (`fast-deflate` feature)
+- Pure-Rust deflate via zlib-rs (default, `zlib-rs` feature)
+- zlib-ng instead, if you want it (`fast-deflate` feature; C, needs cmake)
 - Apple Compression framework support (`apple-compression` feature)
 
 ## Usage
 
 ```rust
-use clawhdf5_filters::{deflate_decode, deflate_encode};
+use clawhdf5_filters::{deflate_compress, deflate_decompress};
 
-let compressed = deflate_encode(&data, 6).unwrap();
-let decompressed = deflate_decode(&compressed).unwrap();
+let compressed = deflate_compress(&data, 6).unwrap();
+// The second argument bounds the output: the expected decompressed size.
+let decompressed = deflate_decompress(&compressed, data.len()).unwrap();
 ```
 
 ## License

crates/clawhdf5-filters/src/fast_deflate.rs

@@ -1,12 +1,13 @@
-//! Fast deflate backends: Apple Compression Framework and zlib-ng.
+//! Deflate backends: Apple Compression Framework, zlib-ng and zlib-rs.
 //!
 //! Backend selection priority (decompression & compression):
 //! 1. Apple Compression Framework (macOS only, `apple-compression` feature)
-//! 2. flate2 with zlib-ng backend (`fast-deflate` feature) or miniz_oxide (default)
+//! 2. flate2 with zlib-ng (`fast-deflate`), else zlib-rs (`zlib-rs`, the
+//!    default), else miniz_oxide
 //!
 //! The Apple Compression Framework uses hardware-accelerated zlib on Apple Silicon
-//! and is typically the fastest option on macOS. zlib-ng is the fastest portable
-//! option and what C HDF5 uses internally.
+//! and is typically the fastest option on macOS. zlib-rs is a pure-Rust port of
+//! zlib-ng; see `BENCHMARKS.md` for how the two compare.
 
 // ---------------------------------------------------------------------------
 // Apple Compression Framework FFI (macOS only)
@@ -243,65 +244,117 @@ mod apple {
 }
 
 // ---------------------------------------------------------------------------
-// Streaming decompression via flate2 (uses zlib-ng when fast-deflate enabled)
+// One-shot (de)compression via flate2 (whichever backend flate2 was built with)
+//
+// The whole input goes to the codec in one call, into an output buffer sized
+// up front. `flate2::read::ZlibDecoder` / `write::ZlibEncoder` stream through a
+// 32 KiB buffer instead, which cost zlib-rs up to 3.7x against zlib-ng on a
+// 1 MB chunk. clawhdf5-format's deflate filter does the same; see
+// `BENCHMARKS.md`, "Deflate backend".
 // ---------------------------------------------------------------------------
 
-/// Streaming decompress with pre-allocated output buffer.
-///
-/// When the output size is known (typical for HDF5 chunks), this avoids
-/// dynamic reallocation by writing directly into a pre-sized buffer.
+/// Decompress into a buffer pre-sized to `output_size`, the expected
+/// decompressed length (known for HDF5 chunks). Output longer than that is an
+/// error, as is a stream that ends early.
 pub(crate) fn flate2_decompress_preallocated(
     data: &[u8],
     output_size: usize,
 ) -> Result<Vec<u8>, String> {
-    use std::io::Read;
-    let mut decoder = flate2::read::ZlibDecoder::new(data);
-    let mut output = vec![0u8; output_size];
-    let mut total_read = 0;
-
-    loop {
-        match decoder.read(&mut output[total_read..]) {
-            Ok(0) => break,
-            Ok(n) => total_read += n,
-            Err(e) => return Err(e.to_string()),
-        }
-    }
-    output.truncate(total_read);
-    Ok(output)
+    inflate_bounded(data, output_size, output_size)
 }
 
 /// Absolute ceiling on decompressed output when the caller has no size hint,
 /// preventing unbounded allocation from a hostile/corrupted zlib stream.
 const MAX_DECOMPRESS_SIZE: usize = 256 * 1024 * 1024;
 
-/// Streaming decompress with dynamic sizing (when output size is unknown).
-///
-/// Bounded by [`MAX_DECOMPRESS_SIZE`] since there is no chunk-size hint to
-/// validate against here — an unbounded `read_to_end` would let a hostile
-/// zlib stream force arbitrarily large allocation (a "zlib bomb").
+/// Decompress with no size hint, bounded by [`MAX_DECOMPRESS_SIZE`] so a
+/// hostile zlib stream cannot force arbitrarily large allocation (a "zlib
+/// bomb").
 pub(crate) fn flate2_decompress_streaming(data: &[u8]) -> Result<Vec<u8>, String> {
-    use std::io::Read;
-    let decoder = flate2::read::ZlibDecoder::new(data);
-    let mut result = Vec::new();
-    decoder
-        .take(MAX_DECOMPRESS_SIZE as u64 + 1)
-        .read_to_end(&mut result)
-        .map_err(|e| e.to_string())?;
-    if result.len() > MAX_DECOMPRESS_SIZE {
-        return Err(format!(
+    let hint = data.len().saturating_mul(4).min(1 << 20);
+    inflate_bounded(data, hint, MAX_DECOMPRESS_SIZE).map_err(|e| {
+        if e.ends_with("exceeds size limit") {
+            format!(
                 "decompressed output exceeds {} MiB limit",
                 MAX_DECOMPRESS_SIZE / 1024 / 1024
-        ));
+            )
+        } else {
+            e
         }
-    Ok(result)
+    })
 }
 
-/// Compress data using flate2 (zlib-ng when fast-deflate enabled, else miniz_oxide).
+/// Inflate a zlib stream, starting from `size_hint` bytes of output and
+/// failing past `limit`.
+fn inflate_bounded(data: &[u8], size_hint: usize, limit: usize) -> Result<Vec<u8>, String> {
+    use flate2::{Decompress, FlushDecompress, Status};
+
+    // One byte of headroom past the limit distinguishes an over-size stream
+    // from one that legitimately ends exactly at the limit.
+    let max_capacity = limit.saturating_add(1);
+    let mut out = Vec::new();
+    out.try_reserve_exact(size_hint.clamp(1, max_capacity))
+        .map_err(|e| format!("deflate: cannot allocate output: {e}"))?;
+
+    let mut inflater = Decompress::new(true);
+    loop {
+        let (in_before, out_before) = (inflater.total_in(), inflater.total_out());
+        let status = inflater
+            .decompress_vec(
+                &data[in_before as usize..],
+                &mut out,
+                FlushDecompress::Finish,
+            )
+            .map_err(|e| format!("deflate: {e}"))?;
+        if out.len() > limit {
+            return Err("deflate: output exceeds size limit".into());
+        }
+        match status {
+            Status::StreamEnd => return Ok(out),
+            Status::Ok | Status::BufError if out.len() == out.capacity() => {
+                let grow = out.capacity().min(max_capacity - out.capacity()).max(1);
+                out.try_reserve_exact(grow)
+                    .map_err(|e| format!("deflate: cannot allocate output: {e}"))?;
+            }
+            Status::Ok | Status::BufError => {
+                if inflater.total_in() as usize >= data.len()
+                    || (inflater.total_in(), inflater.total_out()) == (in_before, out_before)
+                {
+                    return Err("deflate: truncated stream".into());
+                }
+            }
+        }
+    }
+}
+
+/// Compress data using flate2 (zlib-ng, zlib-rs or miniz_oxide; see module docs).
 pub(crate) fn flate2_compress(data: &[u8], level: u32) -> Result<Vec<u8>, String> {
-    use std::io::Write;
-    let mut encoder = flate2::write::ZlibEncoder::new(Vec::new(), flate2::Compression::new(level));
-    encoder.write_all(data).map_err(|e| e.to_string())?;
-    encoder.finish().map_err(|e| e.to_string())
+    use flate2::{Compress, Compression, FlushCompress, Status};
+
+    // zlib's compressBound, plus the zlib header and trailer.
+    let bound = data.len() + (data.len() >> 12) + (data.len() >> 14) + (data.len() >> 25) + 13 + 6;
+    let mut out = Vec::new();
+    out.try_reserve_exact(bound)
+        .map_err(|e| format!("deflate: cannot allocate output: {e}"))?;
+
+    let mut deflater = Compress::new(Compression::new(level), true);
+    loop {
+        let (in_before, out_before) = (deflater.total_in(), deflater.total_out());
+        let status = deflater
+            .compress_vec(&data[in_before as usize..], &mut out, FlushCompress::Finish)
+            .map_err(|e| format!("deflate: {e}"))?;
+        match status {
+            Status::StreamEnd => return Ok(out),
+            Status::Ok | Status::BufError if out.len() == out.capacity() => out
+                .try_reserve(out.capacity().max(4096))
+                .map_err(|e| format!("deflate: cannot allocate output: {e}"))?,
+            Status::Ok | Status::BufError => {
+                if (deflater.total_in(), deflater.total_out()) == (in_before, out_before) {
+                    return Err("deflate: encoder made no progress".into());
+                }
+            }
+        }
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -312,7 +365,7 @@ pub(crate) fn flate2_compress(data: &[u8], level: u32) -> Result<Vec<u8>, String
 ///
 /// Selection order:
 /// 1. Apple Compression Framework (macOS + `apple-compression` feature)
-/// 2. flate2 (zlib-ng with `fast-deflate`, otherwise miniz_oxide)
+/// 2. flate2 (zlib-ng with `fast-deflate`, else zlib-rs, else miniz_oxide)
 ///
 /// When `output_hint` > 0, pre-allocates the output buffer for zero-copy
 /// decompression (avoids reallocation).
@@ -344,7 +397,7 @@ pub fn decompress(data: &[u8], output_hint: usize) -> Result<Vec<u8>, String> {
 ///
 /// Selection order:
 /// 1. Apple Compression Framework (macOS + `apple-compression` feature)
-/// 2. flate2 (zlib-ng with `fast-deflate`, otherwise miniz_oxide)
+/// 2. flate2 (zlib-ng with `fast-deflate`, else zlib-rs, else miniz_oxide)
 pub fn compress(data: &[u8], level: u32) -> Result<Vec<u8>, String> {
     #[cfg(all(target_os = "macos", feature = "apple-compression"))]
     {
@@ -377,9 +430,19 @@ pub fn active_backend() -> &'static str {
     {
         "zlib-ng"
     }
+    // flate2 prefers a C zlib over zlib-rs when both are enabled.
+    #[cfg(all(
+        not(all(target_os = "macos", feature = "apple-compression")),
+        not(feature = "fast-deflate"),
+        feature = "zlib-rs"
+    ))]
+    {
+        "zlib-rs"
+    }
     #[cfg(not(any(
         all(target_os = "macos", feature = "apple-compression"),
-        feature = "fast-deflate"
+        feature = "fast-deflate",
+        feature = "zlib-rs"
     )))]
     {
         "miniz_oxide"
@@ -436,7 +499,7 @@ mod tests {
     fn backend_name_is_set() {
         let name = active_backend();
         assert!(
-            ["miniz_oxide", "zlib-ng", "apple-compression"].contains(&name),
+            ["miniz_oxide", "zlib-rs", "zlib-ng", "apple-compression"].contains(&name),
             "unexpected backend: {name}"
         );
     }

crates/clawhdf5-filters/src/lib.rs

@@ -2,12 +2,14 @@
 //!
 //! Provides deflate (zlib) decompression/compression with multiple backend options:
 //!
-//! - **Default**: `miniz_oxide` (pure Rust, no C dependencies)
-//! - **`fast-deflate` feature**: `zlib-ng` via flate2 (~2-3x faster, matches C HDF5)
+//! - **Default (`zlib-rs` feature)**: `zlib-rs` via flate2 (pure Rust, no C
+//!   dependencies)
+//! - **`fast-deflate` feature**: `zlib-ng` via flate2 (C, built with cmake)
 //! - **`apple-compression` feature**: Apple Compression Framework on macOS
 //!   (hardware-accelerated on Apple Silicon)
+//! - With none of the above: `miniz_oxide` (pure Rust, slower)
 //!
-//! Backend priority: apple-compression > zlib-ng > miniz_oxide.
+//! Backend priority: apple-compression > zlib-ng > zlib-rs > miniz_oxide.
 
 pub mod fast_deflate;
 
@@ -115,7 +117,7 @@ mod tests {
     fn backend_reports_name() {
         let name = deflate_backend();
         assert!(
-            ["miniz_oxide", "zlib-ng", "apple-compression"].contains(&name),
+            ["miniz_oxide", "zlib-rs", "zlib-ng", "apple-compression"].contains(&name),
             "unexpected backend: {name}"
         );
     }

crates/clawhdf5-format/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "clawhdf5-format"
-version = "2.6.0"
+version = "2.7.0"
 edition = "2024"
+rust-version.workspace = true
 description = "Pure-Rust HDF5 binary format parsing and writing — no C dependencies"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
@@ -21,18 +22,33 @@ zstd = { version = "0.13", optional = true }
 blake3 = { version = "1", optional = true }
 libaec-sys = { path = "../libaec-sys", version = "0.1", optional = true }
 pco = { version = "1.0", optional = true }
+# Pure-Rust Zstandard, for the plugin filters that embed zstd (bitshuffle,
+# blosc). The `zstd` feature (filter 32015) links libzstd instead.
+ruzstd = { version = "0.9", optional = true }
+# bzip2 with its default backend, libbz2-rs-sys: a pure-Rust port of
+# libbzip2 (no C is compiled, despite the -sys name).
+bzip2 = { version = "0.6", optional = true }
+snap = { version = "1", optional = true }
+
+[target.'cfg(target_os = "linux")'.dependencies]
+# madvise(MADV_HUGEPAGE) for large read buffers (see src/bulk_alloc.rs).
+libc = { version = "0.2", default-features = false }
 
 [dev-dependencies]
+half = { workspace = true }
 serde_json = "1"
 criterion = { workspace = true }
-clawhdf5-derive = { path = "../clawhdf5-derive", version = "2.6.0" }
+clawhdf5-derive = { path = "../clawhdf5-derive", version = "2.7.0" }
 
 [[bench]]
 name = "bench"
 harness = false
 
 [features]
-default = ["std", "checksum", "deflate", "provenance", "fast-deflate", "system-zlib-decompress"]
+# Deflate backend: `zlib-rs` (pure Rust) by default. `fast-deflate` selects
+# zlib-ng instead (C, built with cmake); flate2 prefers a C zlib whenever one
+# is enabled, so turning it on anywhere in the build overrides the default.
+default = ["std", "checksum", "deflate", "provenance", "zlib-rs", "system-zlib-decompress", "lzf"]
 std = []
 checksum = []
 deflate = ["flate2"]
@@ -42,12 +58,26 @@ fast-checksum = ["crc32fast"]
 fast-deflate = ["flate2/zlib-ng"]
 system-zlib = ["flate2/zlib-default"]
 system-zlib-decompress = []
-zlib-rs = ["flate2/zlib-rs"]
+# `runtime_detection` gives zlib-rs `std`, which it needs to detect and use
+# SIMD at runtime. flate2 enables it by default, but we build flate2 with
+# default-features = false, and without it zlib-rs inflates 3.5x slower.
+zlib-rs = ["flate2/zlib-rs", "flate2/runtime_detection"]
 lz4 = ["lz4_flex"]
 zstd = ["dep:zstd"]
 blake3_hash = ["blake3"]
 szip = ["libaec-sys"]
 pcodec = ["dep:pco"]
+# Plugin filters, pure Rust. LZF (32000) is h5py's built-in compression; it
+# has no dependencies, so it is on by default.
+lzf = []
+# Bitshuffle (32008), with its LZ4 and Zstandard modes.
+bitshuffle = ["lz4_flex", "ruzstd"]
+# bzip2 (307).
+bzip2 = ["dep:bzip2", "std"]
+# Blosc 1 (32001) with its BloscLZ, LZ4, Snappy, Zlib and Zstandard codecs.
+blosc = ["lz4_flex", "ruzstd", "snap", "deflate", "std"]
+# Every plugin filter above.
+plugin-filters = ["lzf", "bitshuffle", "bzip2", "blosc"]
 
 [[bench]]
 name = "parallel_decompress_bench"

crates/clawhdf5-format/fuzz/.gitignore

@@ -1 +1,4 @@
 target/
+corpus/
+artifacts/
+coverage/

crates/clawhdf5-format/fuzz/fuzz_targets/fuzz_btree_v2.rs

@@ -1,15 +1,36 @@
 #![no_main]
+use clawhdf5_format::btree_v2::{BTreeV2Header, collect_btree_v2_records};
 use libfuzzer_sys::fuzz_target;
 
 fuzz_target!(|data: &[u8]| {
     for &offset_size in &[4u8, 8] {
         for &length_size in &[4u8, 8] {
-            let _ = clawhdf5_format::btree_v2::BTreeV2Header::parse(
-                data,
-                0,
-                offset_size,
-                length_size,
-            );
+            if let Ok(header) = BTreeV2Header::parse(data, 0, offset_size, length_size) {
+                let _ = collect_btree_v2_records(data, &header, offset_size, length_size);
             }
         }
+    }
+
+    // Parsing a header requires a valid checksum, which random input almost
+    // never has, so the traversal behind it went unfuzzed — and that is where
+    // a node listing itself as its own child overflowed the stack. Take the
+    // header fields straight from the input instead and walk the rest.
+    let Some((fields, file)) = data.split_first_chunk::<20>() else {
+        return;
+    };
+    let header = BTreeV2Header {
+        tree_type: fields[0],
+        node_size: u32::from_le_bytes([fields[1], fields[2], fields[3], fields[4]]),
+        record_size: u16::from_le_bytes([fields[5], fields[6]]),
+        depth: u16::from_le_bytes([fields[7], fields[8]]),
+        root_node_address: u64::from(u32::from_le_bytes([
+            fields[9], fields[10], fields[11], fields[12],
+        ])),
+        num_records_in_root: u16::from_le_bytes([fields[13], fields[14]]),
+        total_records: u64::from(u32::from_le_bytes([
+            fields[15], fields[16], fields[17], fields[18],
+        ])),
+    };
+    let offset_size = if fields[19] & 1 == 0 { 4 } else { 8 };
+    let _ = collect_btree_v2_records(file, &header, offset_size, 8);
 });

crates/clawhdf5-format/src/attribute.rs

@@ -97,7 +97,7 @@ impl AttributeMessage {
             return Ok(Cow::Borrowed(bytes));
         }
         let (file_data, offset_size) = file.ok_or(FormatError::UnresolvedSharedMessage)?;
-        let shared_ref = shared_message::parse_shared_ref(bytes, offset_size)?;
+        let shared_ref = shared_message::parse_shared_ref_sized(bytes, offset_size, length_size)?;
         shared_message::resolve_shared_message(
             file_data,
             &shared_ref,
@@ -362,6 +362,18 @@ fn extract_name(bytes: &[u8]) -> String {
     String::from_utf8_lossy(&bytes[..end]).into_owned()
 }
 
+/// An attribute's datatype gets libhdf5's extra check for a header without
+/// a checksum (see [`Datatype::check_unused_bits`]).
+fn check_in_header(
+    attr: AttributeMessage,
+    header: &ObjectHeader,
+) -> Result<AttributeMessage, FormatError> {
+    if header.version == 1 {
+        attr.datatype.check_unused_bits()?;
+    }
+    Ok(attr)
+}
+
 /// Extract all attribute messages from an object header.
 pub fn extract_attributes(
     header: &ObjectHeader,
@@ -371,7 +383,7 @@ pub fn extract_attributes(
     for msg in &header.messages {
         if msg.msg_type == MessageType::Attribute {
             let attr = AttributeMessage::parse(&msg.data, length_size)?;
-            attrs.push(attr);
+            attrs.push(check_in_header(attr, header)?);
         }
     }
     Ok(attrs)
@@ -394,42 +406,81 @@ pub fn find_attribute<'a>(
 ///
 /// Use this instead of `extract_attributes` when reading files that may use dense storage
 /// (e.g., objects with many attributes, typically >8).
+///
+/// Fails if any attribute cannot be read; see [`extract_attributes_tolerant`]
+/// to read the others.
 pub fn extract_attributes_full(
     file_data: &[u8],
     header: &ObjectHeader,
     offset_size: u8,
     length_size: u8,
+) -> Result<Vec<AttributeMessage>, FormatError> {
+    extract_attributes_with(file_data, header, offset_size, length_size, &mut Err)
+}
+
+/// Like [`extract_attributes_full`], but an attribute that cannot be read
+/// (a corrupt or unsupported attribute message, or a heap object that cannot
+/// be located) is left out and its error returned alongside the attributes
+/// that could be read, instead of failing them all.
+///
+/// Errors in the structures that index the attributes (the Attribute Info
+/// message, the dense-storage heap header or B-tree) still fail the call:
+/// then it is unknown which attributes exist at all.
+pub fn extract_attributes_tolerant(
+    file_data: &[u8],
+    header: &ObjectHeader,
+    offset_size: u8,
+    length_size: u8,
+) -> Result<(Vec<AttributeMessage>, Vec<FormatError>), FormatError> {
+    let mut errors = Vec::new();
+    let attrs = extract_attributes_with(file_data, header, offset_size, length_size, &mut |e| {
+        errors.push(e);
+        Ok(())
+    })?;
+    Ok((attrs, errors))
+}
+
+/// Read every attribute; each one that fails goes to `on_error`, which
+/// either stops the read (returns the error) or skips that attribute.
+fn extract_attributes_with(
+    file_data: &[u8],
+    header: &ObjectHeader,
+    offset_size: u8,
+    length_size: u8,
+    on_error: &mut dyn FnMut(FormatError) -> Result<(), FormatError>,
 ) -> Result<Vec<AttributeMessage>, FormatError> {
     let mut attrs = Vec::new();
 
     // Collect compact attributes (inline in OH)
     for msg in &header.messages {
         if msg.msg_type == MessageType::Attribute {
-            if shared_message::is_shared(msg.flags) {
+            let attr = if shared_message::is_shared(msg.flags) {
                 // Shared attribute: resolve the reference to get actual attribute data
-                let shared_ref = shared_message::parse_shared_ref(&msg.data, offset_size)?;
-                let resolved_data = shared_message::resolve_shared_message(
+                shared_message::parse_shared_ref_sized(&msg.data, offset_size, length_size)
+                    .and_then(|shared_ref| {
+                        shared_message::resolve_shared_message(
                             file_data,
                             &shared_ref,
                             MessageType::Attribute,
                             offset_size,
                             length_size,
-                )?;
-                let attr = AttributeMessage::parse_in_file(
-                    &resolved_data,
+                        )
+                    })
+                    .and_then(|resolved| {
+                        AttributeMessage::parse_in_file(
+                            &resolved,
                             file_data,
                             offset_size,
                             length_size,
-                )?;
-                attrs.push(attr);
+                        )
+                    })
             } else {
-                let attr = AttributeMessage::parse_in_file(
-                    &msg.data,
-                    file_data,
-                    offset_size,
-                    length_size,
-                )?;
-                attrs.push(attr);
+                AttributeMessage::parse_in_file(&msg.data, file_data, offset_size, length_size)
+            };
+            let attr = attr.and_then(|a| check_in_header(a, header));
+            match attr {
+                Ok(attr) => attrs.push(attr),
+                Err(e) => on_error(e)?,
             }
         }
     }
@@ -439,9 +490,15 @@ pub fn extract_attributes_full(
     if let Some(info) = attr_info
         && let Some(fh_addr) = info.fractal_heap_address
     {
-        let dense_attrs =
-            extract_dense_attributes(file_data, &info, fh_addr, offset_size, length_size)?;
-        attrs.extend(dense_attrs);
+        extract_dense_attributes(
+            file_data,
+            &info,
+            fh_addr,
+            offset_size,
+            length_size,
+            &mut attrs,
+            on_error,
+        )?;
     }
 
     Ok(attrs)
@@ -468,7 +525,9 @@ fn extract_dense_attributes(
     fh_addr: u64,
     offset_size: u8,
     length_size: u8,
-) -> Result<Vec<AttributeMessage>, FormatError> {
+    attrs: &mut Vec<AttributeMessage>,
+    on_error: &mut dyn FnMut(FormatError) -> Result<(), FormatError>,
+) -> Result<(), FormatError> {
     // Parse fractal heap
     let fh = FractalHeapHeader::parse(file_data, fh_addr as usize, offset_size, length_size)?;
 
@@ -482,28 +541,32 @@ fn extract_dense_attributes(
     let btree_hdr = BTreeV2Header::parse(file_data, btree_addr as usize, offset_size, length_size)?;
     let records = collect_btree_v2_records(file_data, &btree_hdr, offset_size, length_size)?;
 
-    let mut attrs = Vec::new();
     for record in &records {
         // Per HDF5 spec, both type 8 and type 9 records start with heap_id:
         //   Type 8: heap_id(8) + msg_flags(1) + creation_order(4) + hash(4)
         //   Type 9: heap_id(8) + msg_flags(1) + creation_order(4)
-        let id_offset = 0;
-
-        if record.data.len() < id_offset + fh.heap_id_length as usize {
+        let id_len = fh.heap_id_length as usize;
+        let Some(id_bytes) = record.data.get(..id_len) else {
+            on_error(FormatError::UnexpectedEof {
+                expected: id_len,
+                available: record.data.len(),
+            })?;
             continue;
-        }
-        let id_bytes = &record.data[id_offset..id_offset + fh.heap_id_length as usize];
-
-        // Read attribute message from fractal heap
-        let attr_data = fh.read_managed_object(file_data, id_bytes, offset_size)?;
+        };
 
         // The data in the heap is a complete attribute message
-        let attr =
-            AttributeMessage::parse_in_file(&attr_data, file_data, offset_size, length_size)?;
-        attrs.push(attr);
+        let attr = fh
+            .read_managed_object(file_data, id_bytes, offset_size)
+            .and_then(|attr_data| {
+                AttributeMessage::parse_in_file(&attr_data, file_data, offset_size, length_size)
+            });
+        match attr {
+            Ok(attr) => attrs.push(attr),
+            Err(e) => on_error(e)?,
+        }
     }
 
-    Ok(attrs)
+    Ok(())
 }
 
 #[cfg(test)]
@@ -523,7 +586,8 @@ mod tests {
 
     /// Build an f64 LE datatype message.
     fn build_f64_dt() -> Vec<u8> {
-        let mut buf = build_dt_header(1, 1, [0x00, 0x00, 0x02], 8);
+        // Sign bit 63 (bits 8-15 of the class bits).
+        let mut buf = build_dt_header(1, 1, [0x20, 63, 0x00], 8);
         let mut props = [0u8; 12];
         props[2..4].copy_from_slice(&64u16.to_le_bytes()); // bit_precision
         props[4] = 52; // exp_location

crates/clawhdf5-format/src/btree_v2.rs

@@ -172,6 +172,17 @@ fn max_records_leaf(node_size: u32, record_size: u16) -> u64 {
     ((node_size - overhead) / record_size as u32) as u64
 }
 
+/// Deepest B-tree v2 accepted. See [`collect_btree_v2_records`].
+const MAX_DEPTH: u16 = 64;
+
+/// Take `n` records from the traversal's budget, or refuse the tree.
+fn spend(budget: &mut usize, n: usize) -> Result<(), FormatError> {
+    *budget = budget
+        .checked_sub(n)
+        .ok_or(FormatError::NestingDepthExceeded)?;
+    Ok(())
+}
+
 /// Collect all records from a B-tree v2 by traversing from the root.
 pub fn collect_btree_v2_records(
     file_data: &[u8],
@@ -182,6 +193,22 @@ pub fn collect_btree_v2_records(
     if header.total_records == 0 || header.num_records_in_root == 0 {
         return Ok(Vec::new());
     }
+    // Recursion is one frame per level, and the depth is read from the file:
+    // a crafted header claiming 65 535 levels over a node that is its own
+    // child overflowed the stack. 64 matches the fractal heap's guard, and no
+    // real tree comes close — even at the minimum fan-out of two it would
+    // hold more than 2^64 records.
+    if header.depth > MAX_DEPTH {
+        return Err(FormatError::NestingDepthExceeded);
+    }
+    // A valid tree stores each record once, in its own bytes, so it cannot
+    // hold more records than the file has room for. Children are addresses,
+    // though, and nothing makes them distinct: levels whose children all
+    // point at one shared node below reach it fan-out^depth times, which is
+    // millions of records from a few kilobytes. Counting against what the
+    // file could physically contain bounds that without trusting the
+    // header's own `total_records`.
+    let mut budget = file_data.len() / usize::from(header.record_size.max(1));
 
     let max_leaf_nrec = max_records_leaf(header.node_size, header.record_size);
 
@@ -206,6 +233,7 @@ pub fn collect_btree_v2_records(
             offset_size,
             length_size,
             max_leaf_nrec,
+            &mut budget,
             &mut records,
         )?;
         Ok(records)
@@ -273,6 +301,7 @@ fn collect_internal_records(
     offset_size: u8,
     length_size: u8,
     max_leaf_nrec: u64,
+    budget: &mut usize,
     out: &mut Vec<BTreeV2Record>,
 ) -> Result<(), FormatError> {
     // signature(4) + version(1) + type(1) = 6
@@ -294,39 +323,21 @@ fn collect_internal_records(
     let records_start = pos;
     pos += records_total;
 
-    // Compute sizes for child pointers
-    // max_records at child depth - for variable-width nrec encoding
+    // Child pointer layout, as libhdf5 computes it (H5B2__hdr_init): the
+    // child's record count is always encoded in the width needed for a
+    // *leaf's* maximum, and — below the first internal level — the child
+    // subtree's total record count in the width needed for the most records
+    // a subtree of that depth can hold.
     let child_depth = depth - 1;
-    let max_nrec_child = if child_depth == 0 {
-        max_leaf_nrec
-    } else {
-        // For internal nodes at child_depth, the true max_nrec depends on the
-        // node size, record size, and the recursive width of child pointer
-        // entries (which themselves depend on max_nrec at deeper levels).
-        // Computing the exact value requires iterating from the leaf level
-        // upward, as described in the HDF5 spec (III.A.2 "Computing the Size
-        // of B-tree Nodes").
-        //
-        // We use `max_leaf_nrec * 2` as a conservative upper bound. This
-        // over-estimates the nrec encoding width, which means we may read
-        // slightly more bytes per child pointer than strictly necessary, but
-        // never fewer. The over-read bytes are harmless because we only
-        // decode `num_records` entries (the actual count from the node header).
-        //
-        // Known limitation: for very deep trees (depth > 3) with small record
-        // sizes, the true max could exceed this estimate, causing us to
-        // under-allocate the nrec encoding width and misparse child pointers.
-        // In practice, HDF5 B-tree v2 depths rarely exceed 2-3.
-        max_leaf_nrec * 2
-    };
-    let nrec_width = bytes_for_max_records(max_nrec_child);
-
-    // Total records in subtree width (only if depth > 1)
+    let nrec_width = bytes_for_max_records(max_leaf_nrec);
     let total_nrec_width = if depth > 1 {
-        // Width to hold total records in a subtree
-        // We compute max possible total records at this subtree depth
-        let max_total = header_max_total_records(max_leaf_nrec, depth - 1);
-        bytes_for_max_records(max_total)
+        bytes_for_max_records(cum_max_records(
+            node_size,
+            record_size,
+            offset_size,
+            max_leaf_nrec,
+            child_depth,
+        ))
     } else {
         0
     };
@@ -350,6 +361,8 @@ fn collect_internal_records(
     // We collect child[0] records, then record[0], then child[1], etc.
     for (i, &(child_addr, child_nrec)) in children.iter().enumerate() {
         if child_depth == 0 {
+            // Before parsing, so a refused tree is not also a large allocation.
+            spend(budget, usize::from(child_nrec))?;
             let leaf_recs =
                 parse_leaf_records(file_data, child_addr as usize, child_nrec, record_size)?;
             out.extend(leaf_recs);
@@ -364,6 +377,7 @@ fn collect_internal_records(
                 offset_size,
                 length_size,
                 max_leaf_nrec,
+                budget,
                 out,
             )?;
         }
@@ -393,6 +407,7 @@ fn collect_internal_records(
                     available: file_data.len(),
                 });
             }
+            spend(budget, 1)?;
             out.push(BTreeV2Record {
                 data: file_data[rec_start..rec_end].to_vec(),
             });
@@ -402,14 +417,36 @@ fn collect_internal_records(
     Ok(())
 }
 
-/// Estimate maximum total records at a given depth (for variable-width encoding).
-fn header_max_total_records(max_leaf_nrec: u64, depth: u16) -> u64 {
-    // Conservative: branching factor * max_leaf at each level
-    let mut total = max_leaf_nrec;
-    for _ in 0..depth {
-        total = total.saturating_mul(max_leaf_nrec.max(2));
+/// Most records a subtree whose root is at `depth` can hold (libhdf5's
+/// `cum_max_nrec`): a leaf holds `max_leaf_nrec`; an internal node at depth
+/// `d` holds `max_nrec(d)` records and `max_nrec(d) + 1` subtrees of depth
+/// `d - 1`, where `max_nrec(d)` is what fits in a node once each record is
+/// paired with a child pointer of the width depth `d` needs.
+fn cum_max_records(
+    node_size: u32,
+    record_size: u16,
+    offset_size: u8,
+    max_leaf_nrec: u64,
+    depth: u16,
+) -> u64 {
+    // Internal node overhead: signature(4) + version(1) + type(1) + checksum(4).
+    const PREFIX: u64 = 10;
+    let nrec_width = bytes_for_max_records(max_leaf_nrec) as u64;
+    let mut cum = max_leaf_nrec;
+    let mut cum_width = 0u64;
+    for d in 1..=depth {
+        let ptr = u64::from(offset_size) + nrec_width + if d > 1 { cum_width } else { 0 };
+        let max_nrec = u64::from(node_size)
+            .saturating_sub(PREFIX)
+            .saturating_sub(ptr)
+            / (u64::from(record_size) + ptr).max(1);
+        cum = max_nrec
+            .saturating_add(1)
+            .saturating_mul(cum)
+            .saturating_add(max_nrec);
+        cum_width = bytes_for_max_records(cum) as u64;
     }
-    total
+    cum
 }
 
 #[cfg(test)]
@@ -466,6 +503,130 @@ mod tests {
         buf
     }
 
+    /// An internal node laid out exactly as `collect_internal_records` will
+    /// read it at `depth`: `records` zeroed records, then `children` pointers,
+    /// all to `child_addr` claiming `child_nrec` records.
+    fn internal_node(
+        depth: u16,
+        node_size: u32,
+        record_size: u16,
+        records: usize,
+        children: usize,
+        child_addr: u64,
+        child_nrec: u64,
+    ) -> Vec<u8> {
+        let max_leaf = max_records_leaf(node_size, record_size);
+        let nrec_width = bytes_for_max_records(max_leaf);
+        let total_width = if depth > 1 {
+            bytes_for_max_records(cum_max_records(
+                node_size,
+                record_size,
+                8,
+                max_leaf,
+                depth - 1,
+            ))
+        } else {
+            0
+        };
+        let mut buf = b"BTIN".to_vec();
+        buf.extend_from_slice(&[0, 5]);
+        buf.resize(buf.len() + records * record_size as usize, 0);
+        for _ in 0..children {
+            buf.extend_from_slice(&child_addr.to_le_bytes());
+            buf.extend_from_slice(&child_nrec.to_le_bytes()[..nrec_width]);
+            buf.resize(buf.len() + total_width, 0);
+        }
+        buf
+    }
+
+    fn header(depth: u16, root: u64, root_nrec: u16, total: u64) -> BTreeV2Header {
+        BTreeV2Header {
+            tree_type: 5,
+            node_size: 512,
+            record_size: 8,
+            depth,
+            root_node_address: root,
+            num_records_in_root: root_nrec,
+            total_records: total,
+        }
+    }
+
+    #[test]
+    fn a_node_that_is_its_own_child_is_rejected_not_recursed() {
+        // One internal node whose two children are itself, under a header
+        // claiming the deepest tree a u16 allows. The layout stops depending
+        // on depth once the subtree-total width saturates, so every level
+        // parses cleanly and recursion runs ~65 000 frames deep: before the
+        // cap this overflowed the stack and aborted the process, from a file
+        // of under 100 bytes.
+        let mut data = internal_node(u16::MAX, 512, 8, 1, 2, 0, 1);
+        data.resize(4096, 0);
+        let result = collect_btree_v2_records(&data, &header(u16::MAX, 0, 1, 1), 8, 8);
+        assert!(result.is_err(), "{result:?}");
+    }
+
+    #[test]
+    fn a_shared_subtree_cannot_multiply_the_work() {
+        // A chain of distinct levels, each node's children all pointing at the
+        // single node below, ending in a real leaf. Every node parses and
+        // nothing is cyclic, yet the leaf is reached fan-out^depth times: 62
+        // children over 4 levels is ~15 million leaf visits from a few
+        // kilobytes. A valid tree cannot hold more records than the file has
+        // room for, so that bounds the traversal instead.
+        let (node_size, record_size) = (512u32, 8u16);
+        let fanout = 62usize;
+        let depth = 4u16;
+        let leaf = build_leaf_node(5, &[&[0u8; 8][..]]);
+
+        // Lay out root first, then each lower level, then the leaf.
+        let mut nodes: Vec<Vec<u8>> = Vec::new();
+        let mut addrs = Vec::new();
+        let mut at = 0u64;
+        let mut sizes = Vec::new();
+        for d in (1..=depth).rev() {
+            let n = internal_node(d, node_size, record_size, fanout - 1, fanout, 0, 0);
+            sizes.push(n.len());
+        }
+        for size in &sizes {
+            addrs.push(at);
+            at += *size as u64;
+        }
+        let leaf_addr = at;
+        for (i, d) in (1..=depth).rev().enumerate() {
+            let (child, child_nrec) = if d == 1 {
+                (leaf_addr, 1)
+            } else {
+                (addrs[i + 1], fanout as u64 - 1)
+            };
+            nodes.push(internal_node(
+                d,
+                node_size,
+                record_size,
+                fanout - 1,
+                fanout,
+                child,
+                child_nrec,
+            ));
+        }
+        let mut data: Vec<u8> = nodes.concat();
+        data.extend_from_slice(&leaf);
+        data.resize(data.len() + 64, 0);
+
+        let started = std::time::Instant::now();
+        let result =
+            collect_btree_v2_records(&data, &header(depth, 0, fanout as u16 - 1, u64::MAX), 8, 8);
+        assert!(
+            result.is_err(),
+            "expected a refusal, got {} records",
+            result.map_or(0, |r| r.len())
+        );
+        assert!(
+            started.elapsed() < std::time::Duration::from_secs(2),
+            "took {:?}",
+            started.elapsed()
+        );
+    }
+
     #[test]
     fn parse_header() {
         let data = build_btree_v2_header(5, 512, 11, 0, 0x1000, 3, 3, 8, 8);
@@ -522,4 +683,18 @@ mod tests {
         let records = collect_btree_v2_records(&header, &hdr, 8, 8).unwrap();
         assert!(records.is_empty());
     }
+
+    #[test]
+    fn subtree_capacity_matches_libhdf5() {
+        // A link-name index (11-byte records, 512-byte nodes, 8-byte
+        // addresses): libhdf5's H5B2__hdr_init gives 45 records per leaf,
+        // then cum_max_nrec 1 149 at depth 1 and 26 449 at depth 2 — two
+        // bytes of subtree count in a depth-3 root's child pointers, where
+        // leaf_max^3 = 91 125 would need three.
+        let leaf = max_records_leaf(512, 11);
+        assert_eq!(leaf, 45);
+        assert_eq!(cum_max_records(512, 11, 8, leaf, 0), 45);
+        assert_eq!(cum_max_records(512, 11, 8, leaf, 1), 1_149);
+        assert_eq!(cum_max_records(512, 11, 8, leaf, 2), 26_449);
+    }
 }

crates/clawhdf5-format/src/bulk_alloc.rs

@@ -0,0 +1,79 @@
+//! Large output buffers backed by transparent huge pages where the OS offers
+//! them.
+//!
+//! A fresh multi-megabyte `Vec` is mapped lazily by the kernel: the first
+//! write to each 4 KiB page takes a page fault, and the kernel zeroes the page
+//! before handing it over. For a 64 MiB read that is 16384 faults, and they
+//! cost far more than the copy that fills the buffer — single-threaded
+//! contiguous reads ran at about a quarter of h5py's speed because of them.
+//! numpy (so h5py) avoids this by asking for transparent huge pages
+//! (`madvise(MADV_HUGEPAGE)`) on every allocation of 4 MiB or more, which
+//! turns 512 faults into one; this module does the same.
+//!
+//! The advice only changes how the pages are backed, never their contents, so
+//! it is harmless when it cannot be honoured (THP disabled, not Linux, a
+//! region that is part of the heap): the buffer is then exactly what it would
+//! have been without it.
+
+#[cfg(not(feature = "std"))]
+use alloc::vec::Vec;
+
+/// Buffers smaller than this are left alone (numpy uses the same threshold).
+#[cfg(any(target_os = "linux", test))]
+pub(crate) const HUGE_PAGE_THRESHOLD: usize = 4 << 20;
+
+/// Advise the kernel to back `[ptr, ptr + len)` with transparent huge pages,
+/// when `len` is large enough to benefit. Call it before the first write so
+/// the faults happen at huge-page granularity.
+#[inline]
+pub(crate) fn advise_huge_pages(ptr: *const u8, len: usize) {
+    #[cfg(target_os = "linux")]
+    if len >= HUGE_PAGE_THRESHOLD {
+        const PAGE: usize = 4096;
+        let start = (ptr as usize).next_multiple_of(PAGE);
+        let end = (ptr as usize + len) & !(PAGE - 1);
+        if end > start {
+            // SAFETY: `[start, end)` lies inside an allocation of `len` bytes
+            // at `ptr` that the caller owns, and is page aligned as madvise
+            // requires. MADV_HUGEPAGE does not change the memory's contents or
+            // validity; on failure (EINVAL when THP is compiled out, etc.) the
+            // region is simply left as it was, so the result is ignored.
+            unsafe {
+                libc::madvise(start as *mut libc::c_void, end - start, libc::MADV_HUGEPAGE);
+            }
+        }
+    }
+    #[cfg(not(target_os = "linux"))]
+    let _ = (ptr, len);
+}
+
+/// `Vec::with_capacity(count)` for a buffer about to be filled in bulk, with
+/// huge-page advice when it is large (see the module docs).
+#[inline]
+pub(crate) fn vec_for_bulk<T>(count: usize) -> Vec<T> {
+    let v: Vec<T> = Vec::with_capacity(count);
+    advise_huge_pages(
+        v.as_ptr().cast::<u8>(),
+        v.capacity().saturating_mul(core::mem::size_of::<T>()),
+    );
+    v
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn bulk_vec_is_an_ordinary_vec() {
+        for count in [0usize, 1, 1000, HUGE_PAGE_THRESHOLD / 4 + 3] {
+            let mut v: Vec<u32> = vec_for_bulk(count);
+            assert!(v.capacity() >= count);
+            v.extend((0..count as u32).map(|i| i.wrapping_mul(2654435761)));
+            assert!(
+                v.iter()
+                    .enumerate()
+                    .all(|(i, &x)| x == (i as u32).wrapping_mul(2654435761))
+            );
+        }
+    }
+}

crates/clawhdf5-format/src/chunk_cache.rs

@@ -223,13 +223,32 @@ pub const DEFAULT_CACHE_BYTES: usize = 16 * 1024 * 1024; // 16 MiB
 /// coordinate map and reduces collision chains compared to power-of-two sizes.
 pub const DEFAULT_MAX_SLOTS: usize = 521;
 
+/// Most datasets whose chunk index a [`ChunkCache`] keeps at once.
+pub const MAX_INDEXED_DATASETS: usize = 64;
+
+/// Most chunk-index entries, summed over all datasets, a [`ChunkCache`] keeps.
+/// Least-recently-used datasets' indexes are dropped past this (the dataset
+/// being read is always kept), so a file with many or huge chunked datasets
+/// cannot grow the cache without bound.
+pub const MAX_INDEXED_CHUNKS: usize = 1 << 20;
+
+/// The dataset key the address-less (legacy) methods use when
+/// [`ChunkCache::ensure_dataset`] has not been called.
+#[cfg(feature = "std")]
+const UNBOUND_DATASET: u64 = u64::MAX;
+
 // ---------------------------------------------------------------------------
 // LRU entry
 // ---------------------------------------------------------------------------
 
+/// Decompressed chunks are keyed by dataset *and* coordinate: every chunked
+/// dataset has a chunk at (0, 0, ...), so the coordinate alone is ambiguous.
+#[cfg(feature = "std")]
+type SlotKey = (u64, ChunkCoord);
+
 #[cfg(feature = "std")]
 struct CachedChunk {
-    coord: ChunkCoord,
+    key: SlotKey,
     /// Shared so a cache hit is a refcount bump, not a copy of the whole
     /// (potentially large) decompressed chunk.
     data: Arc<CacheAlignedBuffer>,
@@ -237,21 +256,48 @@ struct CachedChunk {
     last_access: u64,
 }
 
+/// Per-dataset index state.
+#[cfg(feature = "std")]
+#[derive(Default)]
+struct DatasetEntry {
+    /// Chunk coordinate -> ChunkInfo (offset + size in file).
+    index: Option<Arc<HashMap<ChunkCoord, ChunkInfo>>>,
+    /// Pre-built chunk index for O(1) coordinate lookups.
+    chunk_index: Option<Arc<ChunkIndex>>,
+    /// Pre-computed chunk layout for fast assembly.
+    chunk_layout: Option<Arc<ChunkLayout>>,
+    /// Tick of the last use, for dropping the least recently used dataset.
+    last_used: u64,
+}
+
+#[cfg(feature = "std")]
+impl DatasetEntry {
+    fn weight(&self) -> usize {
+        self.index.as_ref().map_or(0, |m| m.len())
+            + self.chunk_index.as_ref().map_or(0, |c| c.num_chunks())
+    }
+}
+
 // ---------------------------------------------------------------------------
 // ChunkCache
 // ---------------------------------------------------------------------------
 
-/// A per-dataset chunk cache with hash-based index and LRU eviction.
+/// A per-file chunk cache: chunk indexes per dataset, plus an LRU of
+/// decompressed chunks, all keyed by dataset.
 ///
-/// # Usage
+/// A dataset is identified by the address of its chunk index (B-tree, fixed
+/// or extensible array, ...), which is unique within a file. Every method
+/// that takes an `addr` works on that dataset only, so threads reading
+/// different datasets through one shared cache never see each other's
+/// chunks. The address-less methods (`has_index`, `populate_index`,
+/// `get_decompressed`, ...) act on the dataset last bound with
+/// [`Self::ensure_dataset`]; that binding is shared state, so concurrent
+/// readers must use the `*_in` / `*_for` methods instead (the chunked
+/// readers in [`crate::chunked_read`] do).
 ///
-/// ```ignore
-/// let cache = ChunkCache::new();
-/// // Pass &cache to read_chunked_data — it will populate the index lazily.
-/// ```
-///
-/// The cache is wrapped in `Mutex` internally so it can be mutated through
-/// shared references (thread-safe).
+/// Memory is bounded: decompressed data by `max_bytes`/`max_slots` across
+/// all datasets, indexes by [`MAX_INDEXED_DATASETS`] and
+/// [`MAX_INDEXED_CHUNKS`].
 ///
 /// Only available with the `std` feature because it requires `std::sync::Mutex`.
 #[cfg(feature = "std")]
@@ -261,26 +307,20 @@ pub struct ChunkCache {
 
 #[cfg(feature = "std")]
 struct CacheInner {
-    /// Hash index: chunk coordinate -> ChunkInfo (offset + size in file).
-    /// Populated once per dataset on first access.
-    index: Option<HashMap<ChunkCoord, ChunkInfo>>,
+    /// Per-dataset chunk indexes, keyed by chunk-index address.
+    datasets: HashMap<u64, DatasetEntry>,
 
-    /// Address of the dataset (its chunk-index base address) that the cached
-    /// index, chunk index, layout, and decompressed slots currently belong to.
-    /// The cache is shared per file across datasets, so every cached-read entry
-    /// checks this and resets the per-dataset state when the dataset changes —
-    /// otherwise one dataset's chunk index (with its own rank) would be reused
-    /// for another, corrupting reads.
-    index_addr: Option<u64>,
+    /// Dataset the address-less methods act on (see `ensure_dataset`).
+    current: Option<u64>,
 
     /// LRU cache of decompressed chunk data.
     slots: Vec<CachedChunk>,
 
-    /// Coordinate -> index into `slots`, for O(1) lookup instead of a linear
+    /// Key -> index into `slots`, for O(1) lookup instead of a linear
     /// scan. Kept in sync with `slots` on every insert/evict/clear — in
     /// particular, `slots.swap_remove(i)` moves the last element into slot
     /// `i`, so the moved element's index entry must be updated too.
-    slot_index: HashMap<ChunkCoord, usize>,
+    slot_index: HashMap<SlotKey, usize>,
 
     /// Current total bytes of cached decompressed data.
     current_bytes: usize,
@@ -294,17 +334,145 @@ struct CacheInner {
     /// Monotonic counter for LRU ordering.
     tick: u64,
 
-    /// Last accessed chunk coordinate (for sequential detection).
-    last_coord: Option<ChunkCoord>,
+    /// Last accessed chunk (for sequential detection).
+    last_coord: Option<SlotKey>,
 
     /// Access pattern statistics.
     stats: AccessStats,
+}
 
-    /// Pre-built chunk index for O(1) coordinate lookups.
-    chunk_index: Option<ChunkIndex>,
+#[cfg(feature = "std")]
+impl CacheInner {
+    fn current(&self) -> u64 {
+        self.current.unwrap_or(UNBOUND_DATASET)
+    }
 
-    /// Pre-computed chunk layout for fast assembly.
-    chunk_layout: Option<ChunkLayout>,
+    fn touch(&mut self, addr: u64) -> &mut DatasetEntry {
+        self.tick += 1;
+        let tick = self.tick;
+        let entry = self.datasets.entry(addr).or_default();
+        entry.last_used = tick;
+        entry
+    }
+
+    fn entry(&self, addr: u64) -> Option<&DatasetEntry> {
+        self.datasets.get(&addr)
+    }
+
+    /// Drop least-recently-used datasets' indexes (never `keep`'s) until the
+    /// dataset and chunk-entry budgets hold.
+    fn trim_datasets(&mut self, keep: u64) {
+        loop {
+            let total: usize = self.datasets.values().map(DatasetEntry::weight).sum();
+            if self.datasets.len() <= MAX_INDEXED_DATASETS && total <= MAX_INDEXED_CHUNKS {
+                return;
+            }
+            let victim = self
+                .datasets
+                .iter()
+                .filter(|(a, _)| **a != keep)
+                .min_by_key(|(_, e)| e.last_used)
+                .map(|(a, _)| *a);
+            match victim {
+                Some(a) => {
+                    self.datasets.remove(&a);
+                }
+                None => return,
+            }
+        }
+    }
+
+    fn get_decompressed(&mut self, addr: u64, coord: &[u64]) -> Option<Arc<CacheAlignedBuffer>> {
+        self.tick += 1;
+        let tick = self.tick;
+
+        // Track sequential vs random access
+        let is_sequential = self.last_coord.as_ref().is_some_and(|(prev_addr, prev)| {
+            // Sequential if exactly one dimension changed
+            let changes: usize = prev
+                .iter()
+                .zip(coord.iter())
+                .filter(|(a, b)| a != b)
+                .count();
+            *prev_addr == addr && changes <= 1
+        });
+        if is_sequential {
+            self.stats.sequential_count += 1;
+        } else if self.last_coord.is_some() {
+            self.stats.random_count += 1;
+        }
+        let key: SlotKey = (addr, coord.to_vec());
+        let found = if let Some(&idx) = self.slot_index.get(&key) {
+            self.slots[idx].last_access = tick;
+            Some(Arc::clone(&self.slots[idx].data))
+        } else {
+            None
+        };
+        self.last_coord = Some(key);
+        if let Some(ref data) = found {
+            self.stats.hits += 1;
+            self.stats.bytes_read += data.len() as u64;
+        } else {
+            self.stats.misses += 1;
+        }
+        found
+    }
+
+    fn put_decompressed(
+        &mut self,
+        key: SlotKey,
+        data: Arc<CacheAlignedBuffer>,
+    ) -> Arc<CacheAlignedBuffer> {
+        let data_len = data.len();
+
+        // Don't cache if single chunk exceeds budget — still return the data
+        // to the caller, just don't retain it.
+        if data_len > self.max_bytes {
+            return data;
+        }
+
+        // Check if already present
+        self.tick += 1;
+        let tick = self.tick;
+        if let Some(&idx) = self.slot_index.get(&key) {
+            self.slots[idx].last_access = tick;
+            return Arc::clone(&self.slots[idx].data); // already cached
+        }
+
+        // Evict until we have room
+        while self.slots.len() >= self.max_slots
+            || (self.current_bytes + data_len > self.max_bytes && !self.slots.is_empty())
+        {
+            // Find LRU slot
+            let lru_idx = self
+                .slots
+                .iter()
+                .enumerate()
+                .min_by_key(|(_, s)| s.last_access)
+                .map(|(i, _)| i)
+                .unwrap();
+            let removed = self.slots.swap_remove(lru_idx);
+            self.slot_index.remove(&removed.key);
+            // swap_remove moved the former last element into `lru_idx` (unless
+            // it *was* the last element) — fix up that element's index entry.
+            if lru_idx < self.slots.len() {
+                let moved_key = self.slots[lru_idx].key.clone();
+                self.slot_index.insert(moved_key, lru_idx);
+            }
+            self.current_bytes -= removed.data.len();
+            self.stats.evictions += 1;
+        }
+
+        self.current_bytes += data_len;
+        let new_idx = self.slots.len();
+        self.slot_index.insert(key.clone(), new_idx);
+        self.slots.push(CachedChunk {
+            key,
+            data: Arc::clone(&data),
+            last_access: tick,
+        });
+        data
+    }
 }
 
 /// Access pattern statistics tracked by the chunk cache.
@@ -356,8 +524,8 @@ impl ChunkCache {
     pub fn with_capacity(max_bytes: usize, max_slots: usize) -> Self {
         Self {
             inner: std::sync::Mutex::new(CacheInner {
-                index: None,
-                index_addr: None,
+                datasets: HashMap::new(),
+                current: None,
                 slots: Vec::with_capacity(max_slots.min(64)),
                 slot_index: HashMap::with_capacity(max_slots.min(64)),
                 current_bytes: 0,
@@ -366,340 +534,331 @@ impl ChunkCache {
                 tick: 0,
                 last_coord: None,
                 stats: AccessStats::default(),
-                chunk_index: None,
-                chunk_layout: None,
             }),
         }
     }
 
-    // ----- Index operations -----
+    fn lock(&self) -> std::sync::MutexGuard<'_, CacheInner> {
+        self.inner.lock().unwrap_or_else(|e| e.into_inner())
+    }
 
     /// The most decompressed bytes this cache will hold.
     pub fn max_bytes(&self) -> usize {
-        self.inner.lock().map(|g| g.max_bytes).unwrap_or(0)
+        self.lock().max_bytes
     }
 
-    /// Bind the cache to the dataset at chunk-index address `addr`.
+    // ----- Dataset-keyed operations (safe to use concurrently) -----
+
+    /// The chunk list of the dataset whose chunk index is at `addr`.
     ///
-    /// The cache is shared per file across all of its datasets. If the cache
-    /// currently holds state for a different dataset, all per-dataset state
-    /// (chunk index, chunk-index map, layout, and decompressed slots) is
-    /// dropped so the next access rebuilds it for this dataset. Reading the
-    /// same dataset again is a no-op, preserving the cache's benefit for
-    /// repeated/sequential access. Returns `true` if a reset occurred.
+    /// On the first call for a dataset, `build` scans its chunk index; the
+    /// result is kept (offsets truncated to `rank` for the lookup key), so
+    /// later calls skip the scan. `build` runs without the cache lock held;
+    /// if two threads race to build the same dataset's index, the first
+    /// stored one wins and both return equivalent lists.
+    pub fn chunks_for<E>(
+        &self,
+        addr: u64,
+        rank: usize,
+        build: impl FnOnce() -> Result<Vec<ChunkInfo>, E>,
+    ) -> Result<Vec<ChunkInfo>, E> {
+        Ok(self
+            .index_for(addr, rank, build)?
+            .values()
+            .cloned()
+            .collect())
+    }
+
+    fn index_for<E>(
+        &self,
+        addr: u64,
+        rank: usize,
+        build: impl FnOnce() -> Result<Vec<ChunkInfo>, E>,
+    ) -> Result<Arc<HashMap<ChunkCoord, ChunkInfo>>, E> {
+        if let Some(index) = self.lock().touch(addr).index.clone() {
+            return Ok(index);
+        }
+        let chunks = build()?;
+        let map: HashMap<ChunkCoord, ChunkInfo> = chunks
+            .into_iter()
+            .map(|ci| (ci.offsets.iter().take(rank).copied().collect(), ci))
+            .collect();
+        let mut inner = self.lock();
+        let entry = inner.touch(addr);
+        let index = Arc::clone(entry.index.get_or_insert_with(|| Arc::new(map)));
+        inner.trim_datasets(addr);
+        Ok(index)
+    }
+
+    /// The pre-computed assembly layout of the dataset at `addr`, building
+    /// its chunk index (via `build`, as in [`Self::chunks_for`]) and layout on
+    /// first use.
+    pub fn chunk_layout_for<E>(
+        &self,
+        addr: u64,
+        rank: usize,
+        build: impl FnOnce() -> Result<Vec<ChunkInfo>, E>,
+        ds_dims: &[usize],
+        chunk_dims: &[usize],
+        elem_size: usize,
+    ) -> Result<Arc<ChunkLayout>, E> {
+        let (layout, chunk_index) = {
+            let mut inner = self.lock();
+            let entry = inner.touch(addr);
+            (entry.chunk_layout.clone(), entry.chunk_index.clone())
+        };
+        if let Some(layout) = layout {
+            return Ok(layout);
+        }
+        let chunk_index = match chunk_index {
+            Some(ci) => ci,
+            None => {
+                let index = self.index_for(addr, rank, build)?;
+                let chunks: Vec<ChunkInfo> = index.values().cloned().collect();
+                Arc::new(ChunkIndex::build(&chunks, rank))
+            }
+        };
+        let layout = ChunkLayout::build(&chunk_index, ds_dims, chunk_dims, elem_size);
+        let mut inner = self.lock();
+        let entry = inner.touch(addr);
+        entry.chunk_index.get_or_insert(chunk_index);
+        let layout = Arc::clone(entry.chunk_layout.get_or_insert_with(|| Arc::new(layout)));
+        inner.trim_datasets(addr);
+        Ok(layout)
+    }
+
+    /// Cached decompressed chunk at `coord` of the dataset at `addr`.
+    ///
+    /// O(1) lookup; the clone is an `Arc` refcount bump, not a copy of the
+    /// underlying decompressed data.
+    pub fn get_decompressed_in(&self, addr: u64, coord: &[u64]) -> Option<Arc<CacheAlignedBuffer>> {
+        self.lock().get_decompressed(addr, coord)
+    }
+
+    /// Cache decompressed chunk data for `coord` of the dataset at `addr`.
+    /// Returns the `Arc`-shared buffer now cached (or already cached).
+    pub fn put_decompressed_in(
+        &self,
+        addr: u64,
+        coord: ChunkCoord,
+        data: Vec<u8>,
+    ) -> Arc<CacheAlignedBuffer> {
+        self.put_decompressed_aligned_in(addr, coord, CacheAlignedBuffer::from_vec(data))
+    }
+
+    /// [`Self::put_decompressed_in`] for an already-aligned buffer.
+    pub fn put_decompressed_aligned_in(
+        &self,
+        addr: u64,
+        coord: ChunkCoord,
+        data: CacheAlignedBuffer,
+    ) -> Arc<CacheAlignedBuffer> {
+        let data = Arc::new(data);
+        self.lock().put_decompressed((addr, coord), data)
+    }
+
+    /// Record that the given chunk coordinates of the dataset at `addr` are
+    /// predicted to be accessed soon (bookkeeping only).
+    ///
+    /// This does **not** prefetch or pre-decompress anything — it only
+    /// checks whether each coordinate is already in the chunk index and
+    /// updates access-pattern stats accordingly.
+    pub fn prefetch_hint_in(&self, addr: u64, next_coords: &[ChunkCoord]) {
+        let mut inner = self.lock();
+        let Some(index) = inner.entry(addr).and_then(|e| e.index.clone()) else {
+            return;
+        };
+        let known = next_coords
+            .iter()
+            .filter(|c| index.contains_key(*c))
+            .count();
+        inner.stats.sequential_count += known as u64;
+    }
+
+    // ----- Address-less operations on the bound dataset -----
+
+    /// Bind the address-less methods to the dataset at chunk-index address
+    /// `addr`. Returns `true` if this changed the bound dataset.
+    ///
+    /// Each dataset's state is kept separately, so switching loses nothing
+    /// and never exposes one dataset's index or chunks to another. The
+    /// binding itself is shared, though: concurrent readers should use the
+    /// `addr`-taking methods rather than bind and then call these.
     pub fn ensure_dataset(&self, addr: u64) -> bool {
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        if inner.index_addr == Some(addr) {
-            return false;
-        }
-        inner.index = None;
-        inner.chunk_index = None;
-        inner.chunk_layout = None;
-        inner.slots.clear();
-        inner.slot_index.clear();
-        inner.current_bytes = 0;
-        inner.last_coord = None;
-        inner.index_addr = Some(addr);
-        true
+        let mut inner = self.lock();
+        let changed = inner.current != Some(addr);
+        inner.current = Some(addr);
+        changed
     }
 
-    /// Returns `true` if the chunk index has been built.
+    /// Returns `true` if the bound dataset's chunk index has been built.
     pub fn has_index(&self) -> bool {
-        self.inner
-            .lock()
-            .unwrap_or_else(|e| e.into_inner())
-            .index
-            .is_some()
+        let inner = self.lock();
+        inner
+            .entry(inner.current())
+            .is_some_and(|e| e.index.is_some())
     }
 
-    /// Build the chunk index from a pre-collected list of `ChunkInfo`.
+    /// Build the bound dataset's chunk index from a pre-collected list of
+    /// `ChunkInfo`.
     ///
     /// The `rank` parameter is used to truncate offsets to spatial dims only
     /// (B-tree v1 stores rank+1 offsets).
     pub fn populate_index(&self, chunks: &[ChunkInfo], rank: usize) {
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        if inner.index.is_some() {
-            return; // already populated
-        }
-        let mut map = HashMap::with_capacity(chunks.len());
-
-        for ci in chunks {
-            let coord: ChunkCoord = ci.offsets.iter().take(rank).copied().collect();
-            map.insert(coord, ci.clone());
-        }
-        inner.index = Some(map);
+        let addr = self.lock().current();
+        let _ = self.index_for::<core::convert::Infallible>(addr, rank, || Ok(chunks.to_vec()));
     }
 
-    /// Look up a chunk by its spatial coordinate in the index.
+    /// Look up a chunk by its spatial coordinate in the bound dataset's index.
     pub fn lookup_index(&self, coord: &[u64]) -> Option<ChunkInfo> {
-        let inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        inner.index.as_ref()?.get(coord).cloned()
+        let inner = self.lock();
+        inner
+            .entry(inner.current())?
+            .index
+            .as_ref()?
+            .get(coord)
+            .cloned()
     }
 
-    /// Return all indexed chunks as a `Vec<ChunkInfo>` (order unspecified).
+    /// Return all of the bound dataset's indexed chunks (order unspecified).
     pub fn all_indexed_chunks(&self) -> Option<Vec<ChunkInfo>> {
-        let inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        inner.index.as_ref().map(|m| m.values().cloned().collect())
+        let inner = self.lock();
+        let index = inner.entry(inner.current())?.index.as_ref()?;
+        Some(index.values().cloned().collect())
     }
 
-    // ----- Chunk index (pre-built coordinate → ChunkInfo map) -----
-
-    /// Returns `true` if the chunk B-tree index has been built.
+    /// Returns `true` if the bound dataset's `ChunkIndex` has been built.
     pub fn has_chunk_index(&self) -> bool {
-        self.inner
-            .lock()
-            .unwrap_or_else(|e| e.into_inner())
-            .chunk_index
-            .is_some()
+        let inner = self.lock();
+        inner
+            .entry(inner.current())
+            .is_some_and(|e| e.chunk_index.is_some())
     }
 
-    /// Build and store the chunk B-tree index from a pre-collected list of `ChunkInfo`.
+    /// Build and store the bound dataset's `ChunkIndex`.
     pub fn populate_chunk_index(&self, chunks: &[ChunkInfo], rank: usize) {
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        if inner.chunk_index.is_some() {
-            return;
-        }
-        inner.chunk_index = Some(ChunkIndex::build(chunks, rank));
+        let built = Arc::new(ChunkIndex::build(chunks, rank));
+        let mut inner = self.lock();
+        let addr = inner.current();
+        inner.touch(addr).chunk_index.get_or_insert(built);
+        inner.trim_datasets(addr);
     }
 
-    // ----- Chunk layout (pre-computed assembly plan) -----
-
-    /// Returns `true` if the chunk layout has been computed.
+    /// Returns `true` if the bound dataset's chunk layout has been computed.
     pub fn has_chunk_layout(&self) -> bool {
-        self.inner
-            .lock()
-            .unwrap_or_else(|e| e.into_inner())
-            .chunk_layout
-            .is_some()
+        let inner = self.lock();
+        inner
+            .entry(inner.current())
+            .is_some_and(|e| e.chunk_layout.is_some())
     }
 
-    /// Build and store the pre-computed chunk layout for fast assembly.
+    /// Build and store the bound dataset's chunk layout (needs its
+    /// `ChunkIndex`; does nothing without one).
     pub fn populate_chunk_layout(&self, ds_dims: &[usize], chunk_dims: &[usize], elem_size: usize) {
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        if inner.chunk_layout.is_some() {
+        let mut inner = self.lock();
+        let addr = inner.current();
+        let entry = inner.touch(addr);
+        if entry.chunk_layout.is_some() {
             return;
         }
-        if let Some(ref idx) = inner.chunk_index {
-            inner.chunk_layout = Some(ChunkLayout::build(idx, ds_dims, chunk_dims, elem_size));
+        if let Some(idx) = entry.chunk_index.clone() {
+            entry.chunk_layout = Some(Arc::new(ChunkLayout::build(
+                &idx, ds_dims, chunk_dims, elem_size,
+            )));
         }
     }
 
-    /// Execute a function with a reference to the chunk layout.
-    ///
-    /// Returns `None` if the layout hasn't been computed yet.
+    /// Execute a function with a reference to the bound dataset's chunk
+    /// layout. Returns `None` if the layout hasn't been computed yet.
     pub fn with_chunk_layout<F, R>(&self, f: F) -> Option<R>
     where
         F: FnOnce(&ChunkLayout) -> R,
     {
-        let inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        inner.chunk_layout.as_ref().map(f)
+        let layout = {
+            let inner = self.lock();
+            inner.entry(inner.current())?.chunk_layout.clone()?
+        };
+        Some(f(&layout))
     }
 
-    // ----- Decompressed data cache (LRU) -----
-
-    /// Try to get cached decompressed data for a chunk coordinate.
+    /// Try to get cached decompressed data for a chunk of the bound dataset.
     ///
-    /// O(1) lookup. Returns an owned copy for API compatibility with callers
-    /// that need a `Vec<u8>`; prefer [`Self::get_decompressed_aligned`] when
-    /// an `Arc`-shared buffer works for the caller, since that avoids the
-    /// copy entirely.
+    /// Returns an owned copy; prefer [`Self::get_decompressed_aligned`] when
+    /// an `Arc`-shared buffer works for the caller.
     pub fn get_decompressed(&self, coord: &[u64]) -> Option<Vec<u8>> {
         self.get_decompressed_aligned(coord)
             .map(|arc| arc.as_slice().to_vec())
     }
 
-    /// Try to get a reference-counted clone of the aligned buffer for a chunk.
-    ///
-    /// O(1) index lookup; the clone is an `Arc` refcount bump, not a copy of
-    /// the underlying decompressed data.
+    /// Reference-counted cached buffer for a chunk of the bound dataset.
     pub fn get_decompressed_aligned(&self, coord: &[u64]) -> Option<Arc<CacheAlignedBuffer>> {
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        inner.tick += 1;
-        let tick = inner.tick;
-
-        // Track sequential vs random access
-        let is_sequential = inner.last_coord.as_ref().is_some_and(|prev| {
-            // Sequential if exactly one dimension changed
-            let changes: usize = prev
-                .iter()
-                .zip(coord.iter())
-                .filter(|(a, b)| a != b)
-                .count();
-            changes <= 1
-        });
-        if is_sequential {
-            inner.stats.sequential_count += 1;
-        } else if inner.last_coord.is_some() {
-            inner.stats.random_count += 1;
-        }
-        inner.last_coord = Some(coord.to_vec());
-
-        let found = if let Some(&idx) = inner.slot_index.get(coord) {
-            inner.slots[idx].last_access = tick;
-            Some(Arc::clone(&inner.slots[idx].data))
-        } else {
-            None
-        };
-        if let Some(ref data) = found {
-            inner.stats.hits += 1;
-            inner.stats.bytes_read += data.len() as u64;
-        } else {
-            inner.stats.misses += 1;
-        }
-        found
+        let mut inner = self.lock();
+        let addr = inner.current();
+        inner.get_decompressed(addr, coord)
     }
 
-    /// Insert decompressed chunk data into the LRU cache.
-    ///
-    /// The data is stored in a [`CacheAlignedBuffer`] so subsequent reads
-    /// return cache-line-aligned memory. Returns the `Arc`-shared buffer that
-    /// is now cached (or already was), so the caller can reuse it directly
-    /// instead of holding a separate copy of the same data.
+    /// Insert decompressed chunk data for the bound dataset into the LRU
+    /// cache, returning the `Arc`-shared buffer now cached.
     pub fn put_decompressed(&self, coord: ChunkCoord, data: Vec<u8>) -> Arc<CacheAlignedBuffer> {
-        let aligned = CacheAlignedBuffer::from_vec(data);
-        self.put_decompressed_aligned(coord, aligned)
+        self.put_decompressed_aligned(coord, CacheAlignedBuffer::from_vec(data))
     }
 
-    /// Insert an already-aligned buffer into the LRU cache.
-    ///
-    /// Returns the `Arc`-shared buffer now held by the cache (the one just
-    /// inserted, or the existing cached copy if `coord` was already present).
+    /// Insert an already-aligned buffer for the bound dataset.
     pub fn put_decompressed_aligned(
         &self,
         coord: ChunkCoord,
         data: CacheAlignedBuffer,
     ) -> Arc<CacheAlignedBuffer> {
         let data = Arc::new(data);
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        let data_len = data.len();
-
-        // Don't cache if single chunk exceeds budget — still return the data
-        // to the caller, just don't retain it.
-        if data_len > inner.max_bytes {
-            return data;
+        let mut inner = self.lock();
+        let addr = inner.current();
+        inner.put_decompressed((addr, coord), data)
     }
 
-        // Check if already present
-        inner.tick += 1;
-        let tick = inner.tick;
-        if let Some(&idx) = inner.slot_index.get(&coord) {
-            inner.slots[idx].last_access = tick;
-            return Arc::clone(&inner.slots[idx].data); // already cached
+    /// [`Self::prefetch_hint_in`] for the bound dataset.
+    pub fn prefetch_hint(&self, next_coords: &[ChunkCoord]) {
+        let addr = self.lock().current();
+        self.prefetch_hint_in(addr, next_coords);
     }
 
-        // Evict until we have room
-        while inner.slots.len() >= inner.max_slots
-            || (inner.current_bytes + data_len > inner.max_bytes && !inner.slots.is_empty())
-        {
-            // Find LRU slot
-            let lru_idx = inner
-                .slots
-                .iter()
-                .enumerate()
-                .min_by_key(|(_, s)| s.last_access)
-                .map(|(i, _)| i)
-                .unwrap();
-            let removed = inner.slots.swap_remove(lru_idx);
-            inner.slot_index.remove(&removed.coord);
-            // swap_remove moved the former last element into `lru_idx` (unless
-            // it *was* the last element) — fix up that element's index entry.
-            if lru_idx < inner.slots.len() {
-                let moved_coord = inner.slots[lru_idx].coord.clone();
-                inner.slot_index.insert(moved_coord, lru_idx);
-            }
-            inner.current_bytes -= removed.data.len();
-            inner.stats.evictions += 1;
-        }
+    // ----- Whole-cache operations -----
 
-        inner.current_bytes += data_len;
-        let new_idx = inner.slots.len();
-        inner.slot_index.insert(coord.clone(), new_idx);
-        inner.slots.push(CachedChunk {
-            coord,
-            data: Arc::clone(&data),
-            last_access: tick,
-        });
-        data
-    }
-
-    /// Clear the entire cache (index + decompressed data).
+    /// Clear the entire cache (indexes + decompressed data + stats).
     pub fn clear(&self) {
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        inner.index = None;
-        inner.index_addr = None;
+        let mut inner = self.lock();
+        inner.datasets.clear();
+        inner.current = None;
         inner.slots.clear();
         inner.slot_index.clear();
         inner.current_bytes = 0;
         inner.tick = 0;
         inner.last_coord = None;
         inner.stats = AccessStats::default();
-        inner.chunk_index = None;
-        inner.chunk_layout = None;
-    }
-
-    /// Record that the given chunk coordinates are predicted to be accessed
-    /// soon (bookkeeping only).
-    ///
-    /// This does **not** prefetch or pre-decompress anything — it only
-    /// checks whether each coordinate is already in the chunk index and
-    /// updates access-pattern stats accordingly. Real prefetching (e.g.
-    /// background pre-decompression) is not implemented.
-    pub fn prefetch_hint(&self, next_coords: &[ChunkCoord]) {
-        let inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        if inner.index.is_none() {
-            return;
-        }
-        drop(inner);
-        // For each predicted coordinate, verify it exists in the index.
-        // The index is already populated, so this is a no-op for known chunks.
-        // The purpose is to signal intent — callers can pre-decompress if needed.
-        // We touch the stats to record that prefetch hints were issued.
-        let mut inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
-        for coord in next_coords {
-            let exists = inner
-                .index
-                .as_ref()
-                .map(|idx| idx.contains_key(coord))
-                .unwrap_or(false);
-            if exists {
-                inner.stats.sequential_count += 1;
-            }
-        }
     }
 
     /// Return the current access pattern statistics.
     pub fn access_stats(&self) -> AccessStats {
-        self.inner
-            .lock()
-            .unwrap_or_else(|e| e.into_inner())
-            .stats
-            .clone()
+        self.lock().stats.clone()
     }
 
     /// Update the sweep direction label in the access stats.
     pub fn set_sweep_direction(&self, direction: &'static str) {
-        self.inner
-            .lock()
-            .unwrap_or_else(|e| e.into_inner())
-            .stats
-            .sweep_direction = Some(direction);
+        self.lock().stats.sweep_direction = Some(direction);
     }
 
-    /// Number of decompressed chunks currently cached.
+    /// Number of decompressed chunks currently cached (all datasets).
     pub fn cached_chunk_count(&self) -> usize {
-        self.inner
-            .lock()
-            .unwrap_or_else(|e| e.into_inner())
-            .slots
-            .len()
+        self.lock().slots.len()
     }
 
-    /// Total bytes of decompressed data currently cached.
+    /// Total bytes of decompressed data currently cached (all datasets).
     pub fn cached_bytes(&self) -> usize {
-        self.inner
-            .lock()
-            .unwrap_or_else(|e| e.into_inner())
-            .current_bytes
+        self.lock().current_bytes
+    }
+
+    /// Number of datasets whose chunk index is currently kept.
+    pub fn indexed_dataset_count(&self) -> usize {
+        self.lock().datasets.len()
     }
 }
 
@@ -808,6 +967,92 @@ mod tests {
         assert_eq!(cache.cached_bytes(), 0);
     }
 
+    #[test]
+    fn datasets_sharing_coordinates_stay_separate() {
+        let cache = ChunkCache::new();
+        let a = vec![make_chunk(vec![0, 0], 0x100, 8)];
+        let b = vec![make_chunk(vec![0, 0], 0x900, 8)];
+        let got_a = cache.chunks_for::<()>(1, 1, || Ok(a.clone())).unwrap();
+        let got_b = cache.chunks_for::<()>(2, 1, || Ok(b.clone())).unwrap();
+        assert_eq!(got_a[0].address, 0x100);
+        assert_eq!(got_b[0].address, 0x900);
+        // Built once per dataset: a second lookup doesn't call the builder.
+        let again = cache
+            .chunks_for::<()>(1, 1, || panic!("index rebuilt"))
+            .unwrap();
+        assert_eq!(again[0].address, 0x100);
+
+        cache.put_decompressed_in(1, vec![0], vec![1; 4]);
+        cache.put_decompressed_in(2, vec![0], vec![2; 4]);
+        assert_eq!(
+            cache.get_decompressed_in(1, &[0]).unwrap().as_slice(),
+            &[1; 4]
+        );
+        assert_eq!(
+            cache.get_decompressed_in(2, &[0]).unwrap().as_slice(),
+            &[2; 4]
+        );
+        assert!(cache.get_decompressed_in(3, &[0]).is_none());
+        assert_eq!(cache.cached_chunk_count(), 2);
+
+        // The bound-dataset methods see only the bound dataset.
+        cache.ensure_dataset(2);
+        assert_eq!(cache.lookup_index(&[0]).unwrap().address, 0x900);
+        assert_eq!(cache.get_decompressed(&[0]).unwrap(), vec![2; 4]);
+    }
+
+    #[test]
+    fn dataset_indexes_are_bounded() {
+        let cache = ChunkCache::new();
+        for addr in 0..(MAX_INDEXED_DATASETS as u64 + 10) {
+            cache
+                .chunks_for::<()>(addr, 1, || Ok(vec![make_chunk(vec![0], addr, 8)]))
+                .unwrap();
+        }
+        assert_eq!(cache.indexed_dataset_count(), MAX_INDEXED_DATASETS);
+
+        // One huge index evicts the others but is itself kept.
+        let huge: Vec<ChunkInfo> = (0..MAX_INDEXED_CHUNKS as u64)
+            .map(|i| make_chunk(vec![i], i, 8))
+            .collect();
+        let got = cache.chunks_for::<()>(9999, 1, || Ok(huge)).unwrap();
+        assert_eq!(got.len(), MAX_INDEXED_CHUNKS);
+        assert_eq!(cache.indexed_dataset_count(), 1);
+    }
+
+    #[test]
+    fn concurrent_readers_of_different_datasets_see_their_own_chunks() {
+        let cache = std::sync::Arc::new(ChunkCache::with_capacity(1 << 20, 64));
+        let handles: Vec<_> = (0..8u64)
+            .map(|t| {
+                let cache = std::sync::Arc::clone(&cache);
+                std::thread::spawn(move || {
+                    for round in 0..500u64 {
+                        let addr = (t + round) % 16;
+                        let coord = vec![round % 4];
+                        let chunks = cache
+                            .chunks_for::<()>(addr, 1, || {
+                                Ok((0..4).map(|c| make_chunk(vec![c], addr, 8)).collect())
+                            })
+                            .unwrap();
+                        assert!(chunks.iter().all(|c| c.address == addr));
+                        let want = vec![addr as u8; 8];
+                        let got = match cache.get_decompressed_in(addr, &coord) {
+                            Some(hit) => hit.to_vec(),
+                            None => cache
+                                .put_decompressed_in(addr, coord, want.clone())
+                                .to_vec(),
+                        };
+                        assert_eq!(got, want);
+                    }
+                })
+            })
+            .collect();
+        for h in handles {
+            h.join().unwrap();
+        }
+    }
+
     #[test]
     fn duplicate_insert_is_noop() {
         let cache = ChunkCache::new();

crates/clawhdf5-format/src/chunk_grid.rs

@@ -0,0 +1,200 @@
+//! Chunk-index linearisation shared by the Fixed Array and Extensible Array
+//! chunk indexes (reader and writer).
+//!
+//! Both indexes store one element per chunk at a *linear* index, and the
+//! library derives that index from the chunk's scaled coordinates
+//! (`offset / chunk_dim`) using the dataset's **maximum** dimensions, not its
+//! current ones (`H5D__farray_idx_get_addr` / `H5D__earray_idx_get_addr`,
+//! via `layout->max_down_chunks`). A dataset whose current shape is smaller
+//! than its maxshape therefore has gaps in the index, and laying it out by the
+//! current shape puts every chunk after the first row in the wrong place.
+//!
+//! The Extensible Array adds one more step: its one unlimited dimension has no
+//! finite chunk count, so the library *swizzles* the coordinates to make that
+//! dimension the slowest-varying one (`H5VM_swizzle_coords`, which moves
+//! `coords[unlim_dim]` to the front and shifts the dimensions before it right
+//! by one) before linearising with `swizzled_max_down_chunks`. When the
+//! unlimited dimension is already dimension 0 no swizzle happens.
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
+#[cfg(not(feature = "std"))]
+use alloc::{vec, vec::Vec};
+
+use crate::error::FormatError;
+
+/// How a chunk index maps linear element indexes to chunk coordinates.
+#[derive(Debug, Clone)]
+pub(crate) struct ChunkGrid {
+    /// Spatial chunk dimensions, in dataset order.
+    chunk_dims: Vec<u64>,
+    /// Chunks per dimension covering the *current* extent, in dataset order.
+    cur_chunks: Vec<u64>,
+    /// Dataset dimension stored at each linearisation position (slowest
+    /// first). The identity except for a swizzled Extensible Array.
+    order: Vec<usize>,
+    /// Linear stride of each linearisation position.
+    down: Vec<u64>,
+}
+
+impl ChunkGrid {
+    /// Grid for a Fixed Array index: row-major over the chunk counts of the
+    /// maximum dimensions (`max_dims`, falling back to the current dimensions
+    /// when the dataspace records none).
+    pub(crate) fn fixed_array(
+        cur_dims: &[u64],
+        max_dims: Option<&[u64]>,
+        chunk_dims: &[u64],
+    ) -> Result<Self, FormatError> {
+        Self::build(cur_dims, max_dims, chunk_dims, None)
+    }
+
+    /// Grid for an Extensible Array index: like the Fixed Array, but the
+    /// unlimited dimension (the one whose maximum is `H5S_UNLIMITED`) is moved
+    /// to the slowest-varying position first.
+    pub(crate) fn extensible_array(
+        cur_dims: &[u64],
+        max_dims: Option<&[u64]>,
+        chunk_dims: &[u64],
+    ) -> Result<Self, FormatError> {
+        let unlim = max_dims.and_then(|m| m.iter().position(|&d| d == u64::MAX));
+        Self::build(cur_dims, max_dims, chunk_dims, unlim)
+    }
+
+    fn build(
+        cur_dims: &[u64],
+        max_dims: Option<&[u64]>,
+        chunk_dims: &[u64],
+        unlim: Option<usize>,
+    ) -> Result<Self, FormatError> {
+        let rank = chunk_dims.len();
+        if cur_dims.len() != rank || max_dims.is_some_and(|m| m.len() != rank) {
+            return Err(FormatError::ChunkedReadError(
+                "chunk index rank does not match the dataspace".into(),
+            ));
+        }
+        if chunk_dims.contains(&0) {
+            return Err(FormatError::ChunkedReadError(
+                "chunk dimension is zero".into(),
+            ));
+        }
+        let cur_chunks: Vec<u64> = cur_dims
+            .iter()
+            .zip(chunk_dims)
+            .map(|(&d, &c)| d.div_ceil(c))
+            .collect();
+        // Chunk counts of the maximum extent. An unlimited dimension has no
+        // finite count; it only ever sits in the slowest position, where its
+        // count never enters a stride. A (corrupt) maximum smaller than the
+        // current extent is widened so no allocated chunk becomes unreachable.
+        let max_chunks: Vec<u64> = (0..rank)
+            .map(|d| {
+                let max = max_dims.map_or(cur_dims[d], |m| m[d]);
+                if max == u64::MAX {
+                    u64::MAX
+                } else {
+                    max.div_ceil(chunk_dims[d]).max(cur_chunks[d])
+                }
+            })
+            .collect();
+
+        let mut order: Vec<usize> = (0..rank).collect();
+        if let Some(u) = unlim {
+            order.remove(u);
+            order.insert(0, u);
+        }
+        let mut down = vec![1u64; rank];
+        for p in (0..rank.saturating_sub(1)).rev() {
+            let next = max_chunks[order[p + 1]];
+            if next == u64::MAX {
+                // Only reachable with more than one unlimited dimension, which
+                // neither index type can describe.
+                return Err(FormatError::ChunkedReadError(
+                    "array chunk index with more than one unlimited dimension".into(),
+                ));
+            }
+            down[p] = down[p + 1].checked_mul(next).ok_or_else(|| {
+                FormatError::Overflow("chunk index linear stride overflows u64".into())
+            })?;
+        }
+        Ok(Self {
+            chunk_dims: chunk_dims.to_vec(),
+            cur_chunks,
+            order,
+            down,
+        })
+    }
+
+    /// Dataset-space offsets of the chunk stored at linear `index`, or `None`
+    /// when that chunk lies outside the current extent (the index still has a
+    /// slot for it; the library ignores such chunks on read).
+    pub(crate) fn offsets(&self, index: u64) -> Option<Vec<u64>> {
+        let rank = self.chunk_dims.len();
+        let mut offsets = vec![0u64; rank];
+        let mut rem = index;
+        for p in 0..rank {
+            let d = self.order[p];
+            let scaled = rem / self.down[p];
+            rem %= self.down[p];
+            if scaled >= self.cur_chunks[d] {
+                return None;
+            }
+            offsets[d] = scaled * self.chunk_dims[d];
+        }
+        Some(offsets)
+    }
+
+    /// Linear index of the chunk with scaled coordinates `scaled`
+    /// (`offset / chunk_dim` per dimension, in dataset order).
+    pub(crate) fn linear_index(&self, scaled: &[u64]) -> u64 {
+        self.order
+            .iter()
+            .zip(&self.down)
+            .map(|(&d, &stride)| scaled[d] * stride)
+            .sum()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn fixed_array_uses_max_dims() {
+        // shape (4, 6), chunks (2, 3), maxshape (20, 10): 10 x 4 chunk grid.
+        let g = ChunkGrid::fixed_array(&[4, 6], Some(&[20, 10]), &[2, 3]).unwrap();
+        assert_eq!(g.offsets(0), Some(vec![0, 0]));
+        assert_eq!(g.offsets(1), Some(vec![0, 3]));
+        assert_eq!(g.offsets(2), None); // column chunk 2 is beyond the extent
+        assert_eq!(g.offsets(4), Some(vec![2, 0]));
+        assert_eq!(g.offsets(5), Some(vec![2, 3]));
+        assert_eq!(g.offsets(8), None); // row chunk 2 is beyond the extent
+        assert_eq!(g.linear_index(&[1, 1]), 5);
+    }
+
+    #[test]
+    fn extensible_array_swizzles_unlimited_dim() {
+        // maxshape (10, None): dim 1 is unlimited and becomes slowest.
+        let g = ChunkGrid::extensible_array(&[4, 6], Some(&[10, u64::MAX]), &[2, 3]).unwrap();
+        // max chunks of dim 0 = 5, so index = c1 * 5 + c0.
+        assert_eq!(g.linear_index(&[1, 0]), 1);
+        assert_eq!(g.linear_index(&[0, 1]), 5);
+        assert_eq!(g.offsets(5), Some(vec![0, 3]));
+        assert_eq!(g.offsets(6), Some(vec![2, 3]));
+        assert_eq!(g.offsets(2), None);
+    }
+
+    #[test]
+    fn extensible_array_unlimited_first_is_row_major() {
+        let g = ChunkGrid::extensible_array(&[4, 6], Some(&[u64::MAX, 30]), &[2, 3]).unwrap();
+        // max chunks of dim 1 = 10.
+        assert_eq!(g.linear_index(&[1, 1]), 11);
+        assert_eq!(g.offsets(11), Some(vec![2, 3]));
+    }
+
+    #[test]
+    fn rejects_two_unlimited_dims_after_the_first() {
+        assert!(ChunkGrid::fixed_array(&[4, 6], Some(&[u64::MAX, u64::MAX]), &[2, 3]).is_err());
+    }
+}

crates/clawhdf5-format/src/chunked_write.rs

@@ -4,15 +4,17 @@
 extern crate alloc;
 
 #[cfg(not(feature = "std"))]
-use alloc::{vec, vec::Vec};
+use alloc::{format, vec, vec::Vec};
 
 use crate::checksum::jenkins_lookup3;
 use crate::chunk_cache::{CACHE_LINE_SIZE, align_to_cache_line};
+use crate::chunk_grid::ChunkGrid;
 use crate::ea_writer;
 use crate::error::FormatError;
 use crate::filter_pipeline::{
-    FILTER_DEFLATE, FILTER_FLETCHER32, FILTER_LZ4, FILTER_PCODEC, FILTER_SHUFFLE, FILTER_ZSTD,
-    FilterDescription, FilterPipeline,
+    FILTER_BITSHUFFLE, FILTER_BLOSC, FILTER_BZIP2, FILTER_DEFLATE, FILTER_FLETCHER32, FILTER_LZ4,
+    FILTER_LZF, FILTER_PCODEC, FILTER_PCODEC_NAME, FILTER_SHUFFLE, FILTER_ZSTD, FilterDescription,
+    FilterPipeline,
 };
 use crate::filters::compress_chunk;
 /// Round a file offset up to the next cache-line boundary.
@@ -44,8 +46,170 @@ pub struct ChunkOptions {
     pub lz4: bool,
     /// Zstandard compression level (1-22), None = no zstd. Filter ID 32015.
     pub zstd_level: Option<u32>,
-    /// Pcodec lossless numerical compression. Filter ID 32023.
+    /// Pcodec lossless numerical compression. Private, unregistered filter
+    /// ID [`FILTER_PCODEC`] (480): only clawhdf5 can read it.
     pub pcodec: bool,
+    /// A plugin compression filter (LZF, ...). Takes priority over the
+    /// codecs above. Each needs its cargo feature to be written.
+    pub plugin: Option<PluginFilter>,
+}
+
+/// A compression filter from the common HDF5 plugin set, written in the
+/// format the libhdf5 plugin (h5py / hdf5plugin) reads.
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[non_exhaustive]
+pub enum PluginFilter {
+    /// LZF (filter 32000), h5py's built-in `compression="lzf"`. Needs the
+    /// `lzf` feature.
+    Lzf,
+    /// Bitshuffle (filter 32008): a bit transpose of each block of
+    /// `block_size` elements (0 = bitshuffle's default, else a multiple of
+    /// 8), optionally compressed. Needs the `bitshuffle` feature.
+    Bitshuffle {
+        /// Block size in elements; 0 for the default.
+        block_size: u32,
+        /// Compression after the transpose.
+        compression: BitshuffleCompression,
+    },
+    /// bzip2 (filter 307) at block size `level` (1-9). Needs the `bzip2`
+    /// feature.
+    Bzip2 {
+        /// Block size 1-9 (9 = hdf5plugin's default).
+        level: u32,
+    },
+    /// Blosc 1 (filter 32001): `codec` at `level` (0-9; 0 stores), after
+    /// `shuffle`. Needs the `blosc` feature.
+    Blosc {
+        /// The codec inside the Blosc frame.
+        codec: BloscCodec,
+        /// Compression level 0-9 (0 stores the data uncompressed).
+        level: u32,
+        /// The shuffle Blosc applies first.
+        shuffle: BloscShuffle,
+    },
+}
+
+/// The codec inside a Blosc frame that clawhdf5 can write. (It reads
+/// BloscLZ too, but cannot write it.)
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BloscCodec {
+    /// LZ4.
+    Lz4,
+    /// Snappy.
+    Snappy,
+    /// Zlib, at the Blosc level.
+    Zlib,
+    /// Zstandard (clawhdf5's pure-Rust encoder has one level, about zstd 1).
+    Zstd,
+}
+
+/// The shuffle Blosc applies before compressing.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BloscShuffle {
+    /// None.
+    None,
+    /// Byte shuffle (Blosc's default).
+    Byte,
+    /// Bit shuffle.
+    Bit,
+}
+
+/// What bitshuffle compresses its blocks with.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BitshuffleCompression {
+    /// Transpose only.
+    None,
+    /// LZ4 (bitshuffle's `cname="lz4"`, the common choice).
+    Lz4,
+    /// Zstandard. clawhdf5's pure-Rust encoder has a single level (about
+    /// zstd's level 1); `level` is recorded in the file for other writers.
+    Zstd {
+        /// Level recorded in `cd_values[5]`.
+        level: u32,
+    },
+}
+
+impl PluginFilter {
+    /// Whether the filter reorders bytes itself, so the automatic shuffle
+    /// pre-filter would only get in its way.
+    fn shuffles_itself(&self) -> bool {
+        match self {
+            PluginFilter::Lzf => false,
+            PluginFilter::Bitshuffle { .. } => true,
+            PluginFilter::Bzip2 { .. } => false,
+            PluginFilter::Blosc { .. } => true,
+        }
+    }
+
+    /// The pipeline entry for this filter. `chunk_bytes` is one chunk's
+    /// uncompressed size (0 if unknown).
+    fn description(&self, element_size: u32, chunk_bytes: u32) -> FilterDescription {
+        match self {
+            // h5py's lzf_set_local: filter version, liblzf version, chunk
+            // size in bytes. Optional, as h5py flags it: a chunk the filter
+            // cannot shrink may then be stored unfiltered.
+            PluginFilter::Lzf => FilterDescription {
+                filter_id: FILTER_LZF,
+                name: Some("lzf".into()),
+                flags: 1,
+                client_data: vec![4, 0x0105, chunk_bytes],
+            },
+            // bshuf_h5_set_local: version 0.4, element size, block size,
+            // compression (0 none, 2 LZ4, 3 Zstandard), Zstandard level.
+            // hdf5-blosc's blosc_set_local: filter revision 2, Blosc format
+            // 2, type size, chunk size, then level, shuffle, compressor.
+            PluginFilter::Blosc {
+                codec,
+                level,
+                shuffle,
+            } => FilterDescription {
+                filter_id: FILTER_BLOSC,
+                name: Some("blosc".into()),
+                flags: 1,
+                client_data: vec![
+                    2,
+                    2,
+                    element_size,
+                    chunk_bytes,
+                    (*level).min(9),
+                    match shuffle {
+                        BloscShuffle::None => 0,
+                        BloscShuffle::Byte => 1,
+                        BloscShuffle::Bit => 2,
+                    },
+                    match codec {
+                        BloscCodec::Lz4 => 1,
+                        BloscCodec::Snappy => 3,
+                        BloscCodec::Zlib => 4,
+                        BloscCodec::Zstd => 5,
+                    },
+                ],
+            },
+            PluginFilter::Bzip2 { level } => FilterDescription {
+                filter_id: FILTER_BZIP2,
+                name: Some("bzip2".into()),
+                flags: 1,
+                client_data: vec![(*level).clamp(1, 9)],
+            },
+            PluginFilter::Bitshuffle {
+                block_size,
+                compression,
+            } => {
+                let mut cd = vec![0, 4, element_size, *block_size];
+                match compression {
+                    BitshuffleCompression::None => cd.push(0),
+                    BitshuffleCompression::Lz4 => cd.push(2),
+                    BitshuffleCompression::Zstd { level } => cd.extend([3, *level]),
+                }
+                FilterDescription {
+                    filter_id: FILTER_BITSHUFFLE,
+                    name: Some("bitshuffle; see https://github.com/kiyo-masui/bitshuffle".into()),
+                    flags: 1,
+                    client_data: cd,
+                }
+            }
+        }
+    }
 }
 
 /// Largest chunk the automatic choice produces, in bytes.
@@ -90,14 +254,33 @@ impl ChunkOptions {
             || self.lz4
             || self.zstd_level.is_some()
             || self.pcodec
+            || self.plugin.is_some()
     }
 
     /// Build a FilterPipeline from the options.
     pub fn build_pipeline(&self, element_size: u32) -> Option<FilterPipeline> {
+        self.build_pipeline_for_chunk(element_size, 0)
+    }
+
+    /// Build a FilterPipeline for chunks of `chunk_bytes` uncompressed bytes
+    /// (0 if unknown). Some plugin filters record the chunk size in their
+    /// client data.
+    pub fn build_pipeline_for_chunk(
+        &self,
+        element_size: u32,
+        chunk_bytes: u32,
+    ) -> Option<FilterPipeline> {
         let mut filters = Vec::new();
 
-        let has_compression =
-            self.deflate_level.is_some() || self.zstd_level.is_some() || self.lz4 || self.pcodec;
+        let plugin_shuffles = self
+            .plugin
+            .as_ref()
+            .is_some_and(PluginFilter::shuffles_itself);
+        let has_compression = self.deflate_level.is_some()
+            || self.zstd_level.is_some()
+            || self.lz4
+            || self.pcodec
+            || (self.plugin.is_some() && !plugin_shuffles);
 
         // Shuffle before compression. Applied if explicitly requested OR if compression
         // is active and the caller hasn't disabled it — matches h5py default behavior
@@ -111,11 +294,14 @@ impl ChunkOptions {
             });
         }
 
-        // Compression filters (mutually exclusive, priority: pcodec > zstd > lz4 > deflate)
-        if self.pcodec {
+        // Compression filters (mutually exclusive, priority: plugin > pcodec >
+        // zstd > lz4 > deflate)
+        if let Some(plugin) = &self.plugin {
+            filters.push(plugin.description(element_size, chunk_bytes));
+        } else if self.pcodec {
             filters.push(FilterDescription {
                 filter_id: FILTER_PCODEC,
-                name: Some("pcodec".into()),
+                name: Some(FILTER_PCODEC_NAME.into()),
                 flags: 0,
                 client_data: vec![element_size],
             });
@@ -381,39 +567,7 @@ fn serialize_v4_single_chunk(
     let ndims = chunk_dims.len() as u8 + 1;
     buf.push(ndims);
 
-    // dim_size_encoded_length: how many bytes per dimension
-    // We need to figure out the minimum encoding width
-    let max_dim = chunk_dims
-        .iter()
-        .map(|&d| d as u64)
-        .chain(core::iter::once(element_size as u64))
-        .max()
-        .unwrap_or(1);
-    let dim_encoded_len: u8 = if max_dim <= 0xFF {
-        1
-    } else if max_dim <= 0xFFFF {
-        2
-    } else {
-        4
-    };
-    buf.push(dim_encoded_len);
-
-    // dimension sizes (chunk dims + element size)
-    for &d in chunk_dims {
-        match dim_encoded_len {
-            1 => buf.push(d as u8),
-            2 => buf.extend_from_slice(&(d as u16).to_le_bytes()),
-            4 => buf.extend_from_slice(&d.to_le_bytes()),
-            _ => {}
-        }
-    }
-    // Element size dimension
-    match dim_encoded_len {
-        1 => buf.push(element_size as u8),
-        2 => buf.extend_from_slice(&(element_size as u16).to_le_bytes()),
-        4 => buf.extend_from_slice(&element_size.to_le_bytes()),
-        _ => {}
-    }
+    push_v4_chunk_dims(&mut buf, chunk_dims, element_size);
 
     // chunk index type = 1 (single chunk)
     buf.push(1);
@@ -443,45 +597,7 @@ fn serialize_v4_fixed_array(
     element_size: u32,
     max_bits: u8,
 ) -> Vec<u8> {
-    let mut buf = Vec::new();
-    buf.push(4); // version
-    buf.push(2); // class = chunked
-
-    let flags: u8 = 0x00;
-    buf.push(flags);
-
-    let ndims = chunk_dims.len() as u8 + 1;
-    buf.push(ndims);
-
-    let max_dim = chunk_dims
-        .iter()
-        .map(|&d| d as u64)
-        .chain(core::iter::once(element_size as u64))
-        .max()
-        .unwrap_or(1);
-    let dim_encoded_len: u8 = if max_dim <= 0xFF {
-        1
-    } else if max_dim <= 0xFFFF {
-        2
-    } else {
-        4
-    };
-    buf.push(dim_encoded_len);
-
-    for &d in chunk_dims {
-        match dim_encoded_len {
-            1 => buf.push(d as u8),
-            2 => buf.extend_from_slice(&(d as u16).to_le_bytes()),
-            4 => buf.extend_from_slice(&d.to_le_bytes()),
-            _ => {}
-        }
-    }
-    match dim_encoded_len {
-        1 => buf.push(element_size as u8),
-        2 => buf.extend_from_slice(&(element_size as u16).to_le_bytes()),
-        4 => buf.extend_from_slice(&element_size.to_le_bytes()),
-        _ => {}
-    }
+    let mut buf = layout_v4_chunked_prefix(chunk_dims, element_size);
 
     // chunk index type = 3 (Fixed Array)
     buf.push(3);
@@ -499,107 +615,175 @@ fn serialize_v4_fixed_array(
     buf
 }
 
+/// The part of a v4 chunked layout message before the chunk index type:
+/// version, class, flags and the chunk dimensions (plus the element size).
+/// Append a v4 layout's dimension width and its dimensions (the chunk
+/// dimensions, then the element size). Each takes the fewest bytes that hold
+/// the largest, as libhdf5 computes it (`H5D__chunk_set_sizes`:
+/// `(log2(dim) + 8) / 8`); HDF5 2.0.0 refuses any other width.
+pub(crate) fn push_v4_chunk_dims(buf: &mut Vec<u8>, chunk_dims: &[u32], element_size: u32) {
+    let max_dim = chunk_dims
+        .iter()
+        .copied()
+        .chain(core::iter::once(element_size))
+        .max()
+        .unwrap_or(1)
+        .max(1);
+    let width = (32 - max_dim.leading_zeros()).div_ceil(8) as usize;
+    buf.push(width as u8);
+    for &d in chunk_dims.iter().chain(core::iter::once(&element_size)) {
+        buf.extend_from_slice(&d.to_le_bytes()[..width]);
+    }
+}
+
+fn layout_v4_chunked_prefix(chunk_dims: &[u32], element_size: u32) -> Vec<u8> {
+    let mut buf = Vec::new();
+    buf.push(4); // version
+    buf.push(2); // class = chunked
+
+    let flags: u8 = 0x00;
+    buf.push(flags);
+
+    let ndims = chunk_dims.len() as u8 + 1;
+    buf.push(ndims);
+
+    push_v4_chunk_dims(&mut buf, chunk_dims, element_size);
+    buf
+}
+
+/// log2 of the elements per Fixed Array data block page (the library's
+/// default, `H5D_FARRAY_MAX_DBLK_PAGE_NELMTS_BITS`).
+const FA_PAGE_BITS: u8 = 10;
+
+pub(crate) fn push_addr(buf: &mut Vec<u8>, addr: u64, offset_size: u8) {
+    match offset_size {
+        4 => buf.extend_from_slice(&(addr as u32).to_le_bytes()),
+        _ => buf.extend_from_slice(&addr.to_le_bytes()),
+    }
+}
+
+/// Width of the chunk-size field of a filtered chunk index element. Must
+/// match the library's `H5D_FARRAY_FILT_COMPUTE_CHUNK_SIZE_LEN` (the EA and
+/// B-tree v2 indexes use the same formula):
+/// `1 + ((log2(unfiltered chunk bytes) + 8) / 8)`, capped at 8.
+pub(crate) fn filtered_chunk_size_len(slots: &[Option<WrittenChunk>]) -> usize {
+    let max_raw = slots
+        .iter()
+        .flatten()
+        .map(|c| c.raw_size)
+        .max()
+        .unwrap_or(1);
+    let log2_val = if max_raw <= 1 {
+        0
+    } else {
+        63 - max_raw.leading_zeros()
+    };
+    (1 + ((log2_val + 8) / 8) as usize).min(8)
+}
+
+/// Append one chunk index element: the chunk's address, plus its stored size
+/// and filter mask when the dataset is filtered. `None` is an unallocated
+/// chunk (undefined address, zero size and mask).
+pub(crate) fn push_index_element(
+    buf: &mut Vec<u8>,
+    slot: Option<&WrittenChunk>,
+    offset_size: u8,
+    chunk_size_bytes: Option<usize>,
+) {
+    match slot {
+        Some(c) => {
+            push_addr(buf, c.address, offset_size);
+            if let Some(n) = chunk_size_bytes {
+                buf.extend_from_slice(&c.compressed_size.to_le_bytes()[..n]);
+                buf.extend_from_slice(&c.filter_mask.to_le_bytes());
+            }
+        }
+        None => {
+            buf.extend(core::iter::repeat_n(0xFF, offset_size as usize));
+            if let Some(n) = chunk_size_bytes {
+                buf.extend(core::iter::repeat_n(0x00, n + 4));
+            }
+        }
+    }
+}
+
 /// Build a complete Fixed Array at a known absolute address.
+///
+/// `slots` holds one entry per element of the array, i.e. per chunk of the
+/// dataset's *maximum* extent in the order [`crate::chunk_grid`] defines;
+/// `None` marks a chunk that is not allocated. An array with more elements
+/// than fit in one page (`2^FA_PAGE_BITS`) gets a paged data block: a
+/// page-init bitmap after the prefix, then one checksummed page per
+/// `2^FA_PAGE_BITS` elements, the last one short (`H5FA__dblock_create`).
 pub fn build_fixed_array_at(
-    chunks: &[WrittenChunk],
+    slots: &[Option<WrittenChunk>],
     offset_size: u8,
     length_size: u8,
     has_filters: bool,
     fa_base_address: u64,
 ) -> Vec<u8> {
     let os = offset_size as usize;
-    let num_elements = chunks.len();
-
-    // For filtered chunks, compute chunk_size encoding width.
-    // Must match the HDF5 C library's H5D_FARRAY_FILT_COMPUTE_CHUNK_SIZE_LEN macro:
-    //   chunk_size_len = 1 + ((H5VM_log2_gen(chunk.size) + 8) / 8)
-    // where chunk.size is the unfiltered chunk size in bytes (product of all chunk dims).
-    let chunk_size_bytes: usize = if has_filters {
-        let max_raw = chunks.iter().map(|c| c.raw_size).max().unwrap_or(1);
-        let log2_val = if max_raw <= 1 {
-            0
-        } else {
-            63 - max_raw.leading_zeros()
-        };
-        let len = 1 + ((log2_val + 8) / 8) as usize;
-        len.min(8)
-    } else {
-        0
-    };
-
-    let elem_size = if has_filters {
-        os + chunk_size_bytes + 4
-    } else {
-        os
-    };
+    let num_elements = slots.len();
 
+    let chunk_size_bytes = has_filters.then(|| filtered_chunk_size_len(slots));
+    let elem_size = os + chunk_size_bytes.map_or(0, |n| n + 4);
     let client_id: u8 = if has_filters { 1 } else { 0 };
 
     // FAHD total size
-    let nelmts_field_size = length_size as usize;
-    let fahd_total_size = 4 + 1 + 1 + 1 + 1 + nelmts_field_size + os + 4;
+    let fahd_total_size = 4 + 1 + 1 + 1 + 1 + length_size as usize + os + 4;
     let fadb_address = fa_base_address + fahd_total_size as u64;
 
-    // Build FAHD
     let mut fahd = Vec::with_capacity(fahd_total_size);
     fahd.extend_from_slice(b"FAHD");
     fahd.push(0); // version
     fahd.push(client_id);
     fahd.push(elem_size as u8);
-
-    // max_nelmts_bits: use 10 as default (page_size = 1024), matching h5py convention
-    let max_bits: u8 = 10;
-    fahd.push(max_bits);
-
+    fahd.push(FA_PAGE_BITS);
     match length_size {
         4 => fahd.extend_from_slice(&(num_elements as u32).to_le_bytes()),
-        8 => fahd.extend_from_slice(&(num_elements as u64).to_le_bytes()),
         _ => fahd.extend_from_slice(&(num_elements as u64).to_le_bytes()),
     }
-
-    match offset_size {
-        4 => fahd.extend_from_slice(&(fadb_address as u32).to_le_bytes()),
-        8 => fahd.extend_from_slice(&fadb_address.to_le_bytes()),
-        _ => fahd.extend_from_slice(&fadb_address.to_le_bytes()),
-    }
-
-    // Checksum
+    push_addr(&mut fahd, fadb_address, offset_size);
     let checksum = jenkins_lookup3(&fahd);
     fahd.extend_from_slice(&checksum.to_le_bytes());
-
     assert_eq!(fahd.len(), fahd_total_size);
 
-    // Build FADB
+    // FADB prefix
     let mut fadb = Vec::new();
     fadb.extend_from_slice(b"FADB");
     fadb.push(0); // version
     fadb.push(client_id);
+    push_addr(&mut fadb, fa_base_address, offset_size);
 
-    // header address
-    match offset_size {
-        4 => fadb.extend_from_slice(&(fa_base_address as u32).to_le_bytes()),
-        8 => fadb.extend_from_slice(&fa_base_address.to_le_bytes()),
-        _ => fadb.extend_from_slice(&fa_base_address.to_le_bytes()),
+    let page_nelmts = 1usize << FA_PAGE_BITS;
+    if num_elements <= page_nelmts {
+        // Unpaged: the elements follow the prefix, one checksum over both.
+        for slot in slots {
+            push_index_element(&mut fadb, slot.as_ref(), offset_size, chunk_size_bytes);
         }
-
-    // Element data
-    for chunk in chunks {
-        match offset_size {
-            4 => fadb.extend_from_slice(&(chunk.address as u32).to_le_bytes()),
-            8 => fadb.extend_from_slice(&chunk.address.to_le_bytes()),
-            _ => fadb.extend_from_slice(&chunk.address.to_le_bytes()),
-        }
-        if has_filters {
-            // Write compressed size using chunk_size_bytes (variable width)
-            let cs_bytes = chunk.compressed_size.to_le_bytes();
-            fadb.extend_from_slice(&cs_bytes[..chunk_size_bytes]);
-            fadb.extend_from_slice(&chunk.filter_mask.to_le_bytes());
-        }
-    }
-
-    // FADB checksum
         let fadb_checksum = jenkins_lookup3(&fadb);
         fadb.extend_from_slice(&fadb_checksum.to_le_bytes());
+    } else {
+        // Paged: every page is written, so every page-init bit is set
+        // (MSB-first, as `H5VM_bit_set` packs them). The prefix and bitmap
+        // share a checksum; each page carries its own.
+        let npages = num_elements.div_ceil(page_nelmts);
+        let mut bitmap = vec![0u8; npages.div_ceil(8)];
+        for p in 0..npages {
+            bitmap[p / 8] |= 0x80 >> (p % 8);
+        }
+        fadb.extend_from_slice(&bitmap);
+        let prefix_checksum = jenkins_lookup3(&fadb);
+        fadb.extend_from_slice(&prefix_checksum.to_le_bytes());
+        for page in slots.chunks(page_nelmts) {
+            let start = fadb.len();
+            for slot in page {
+                push_index_element(&mut fadb, slot.as_ref(), offset_size, chunk_size_bytes);
+            }
+            let page_checksum = jenkins_lookup3(&fadb[start..]);
+            fadb.extend_from_slice(&page_checksum.to_le_bytes());
+        }
+    }
 
     let mut combined = fahd;
     combined.extend_from_slice(&fadb);
@@ -634,7 +818,12 @@ pub fn precompress_chunks(
     element_size: usize,
     options: &ChunkOptions,
 ) -> Result<PrecompressedChunks, FormatError> {
-    let pipeline = options.build_pipeline(element_size as u32);
+    let chunk_bytes = chunk_dims
+        .iter()
+        .try_fold(element_size as u64, |acc, &d| acc.checked_mul(d))
+        .and_then(|b| u32::try_from(b).ok())
+        .unwrap_or(0);
+    let pipeline = options.build_pipeline_for_chunk(element_size as u32, chunk_bytes);
     let has_filters = pipeline.is_some();
     let pipeline_message = pipeline.as_ref().map(|pl| pl.serialize());
 
@@ -667,7 +856,8 @@ pub fn build_chunked_data_from_precompressed(
     pre: &PrecompressedChunks,
     base_address: u64,
     maxshape: Option<&[u64]>,
-) -> ChunkedDataResult {
+) -> Result<ChunkedDataResult, FormatError> {
+    let index = ChunkIndexPlan::new(&pre.shape, maxshape, &pre.chunk_dims)?;
     let offset_size: u8 = 8;
     let length_size: u8 = 8;
     let num_chunks = pre.chunks.len();
@@ -693,17 +883,18 @@ pub fn build_chunked_data_from_precompressed(
     }
 
     let chunk_dims_u32: Vec<u32> = pre.chunk_dims.iter().map(|&d| d as u32).collect();
-    let use_extensible = maxshape.is_some_and(|ms| ms.contains(&u64::MAX));
 
     let aligned_idx = align_to_cache_line(data_buf.len());
     if aligned_idx > data_buf.len() {
         data_buf.resize(aligned_idx, 0u8);
     }
 
-    let layout_message = if use_extensible {
+    let layout_message = match &index {
+        ChunkIndexPlan::ExtensibleArray(grid) => {
             let ea_address = base_address + data_buf.len() as u64;
+            let slots = index_slots(grid, &pre.shape, &pre.chunk_dims, &written_chunks, None)?;
             let ea_bytes = ea_writer::build_extensible_array_at(
-            &written_chunks,
+                &slots,
                 offset_size,
                 length_size,
                 pre.has_filters,
@@ -716,7 +907,8 @@ pub fn build_chunked_data_from_precompressed(
                 offset_size,
                 element_size as u32,
             )
-    } else if num_chunks == 1 {
+        }
+        ChunkIndexPlan::SingleChunk => {
             let chunk_addr = written_chunks[0].address;
             let filtered_size = if pre.has_filters {
                 Some(written_chunks[0].compressed_size)
@@ -732,10 +924,18 @@ pub fn build_chunked_data_from_precompressed(
                 offset_size,
                 element_size as u32,
             )
-    } else {
+        }
+        ChunkIndexPlan::FixedArray(grid, nslots) => {
             let fa_address = base_address + data_buf.len() as u64;
-        let fa_bytes = build_fixed_array_at(
+            let slots = index_slots(
+                grid,
+                &pre.shape,
+                &pre.chunk_dims,
                 &written_chunks,
+                Some(*nslots),
+            )?;
+            let fa_bytes = build_fixed_array_at(
+                &slots,
                 offset_size,
                 length_size,
                 pre.has_filters,
@@ -747,15 +947,263 @@ pub fn build_chunked_data_from_precompressed(
                 fa_address,
                 offset_size,
                 element_size as u32,
-            10, // max_nelmts_bits — matches h5py convention
+                FA_PAGE_BITS,
             )
+        }
+        ChunkIndexPlan::BTreeV2 => {
+            let bt_address = base_address + data_buf.len() as u64;
+            let records: Vec<(Vec<u64>, &WrittenChunk)> = written_chunks
+                .iter()
+                .enumerate()
+                .map(|(i, c)| (scaled_coords(&pre.shape, &pre.chunk_dims, i), c))
+                .collect();
+            let (bt_bytes, node_size) = build_btree_v2_chunk_index_at(
+                pre.shape.len(),
+                &records,
+                offset_size,
+                length_size,
+                pre.has_filters,
+                bt_address,
+            )?;
+            data_buf.extend_from_slice(&bt_bytes);
+            serialize_v4_btree_v2(
+                &chunk_dims_u32,
+                bt_address,
+                offset_size,
+                element_size as u32,
+                node_size,
+            )
+        }
     };
 
-    ChunkedDataResult {
+    Ok(ChunkedDataResult {
         data_bytes: data_buf,
         layout_message,
         pipeline_message: pre.pipeline_message.clone(),
+    })
+}
+
+/// Most slots a Fixed Array index may have before we refuse to build it: its
+/// data block holds one element per chunk of the *maximum* extent, so a huge
+/// finite maxshape with small chunks would otherwise exhaust memory.
+const MAX_FIXED_ARRAY_SLOTS: u64 = 1 << 26;
+
+/// Which chunk index a dataset gets, following the library's choice in
+/// `H5D__layout_set_latest_indexing`: version-2 B-tree for more than one
+/// unlimited dimension, Extensible Array for exactly one, Fixed Array for a
+/// finite maxshape, Single Chunk when the whole maximum extent is one chunk.
+enum ChunkIndexPlan {
+    SingleChunk,
+    /// The grid and the number of array elements (chunks of the max extent).
+    FixedArray(ChunkGrid, usize),
+    ExtensibleArray(ChunkGrid),
+    BTreeV2,
+}
+
+impl ChunkIndexPlan {
+    fn new(
+        shape: &[u64],
+        maxshape: Option<&[u64]>,
+        chunk_dims: &[u64],
+    ) -> Result<Self, FormatError> {
+        let bad = |what: &str| FormatError::ChunkedReadError(format!("maxshape: {what}"));
+        if let Some(ms) = maxshape {
+            if ms.len() != shape.len() {
+                return Err(bad("rank differs from the shape"));
             }
+            if ms.iter().zip(shape).any(|(&m, &s)| m < s) {
+                return Err(bad("smaller than the shape"));
+            }
+        }
+        let max = maxshape.unwrap_or(shape);
+        let nunlim = max.iter().filter(|&&d| d == u64::MAX).count();
+        match nunlim {
+            0 => {
+                let nslots = max
+                    .iter()
+                    .zip(chunk_dims)
+                    .try_fold(1u64, |acc, (&m, &c)| acc.checked_mul(m.div_ceil(c.max(1))))
+                    .filter(|&n| n <= MAX_FIXED_ARRAY_SLOTS)
+                    .ok_or_else(|| {
+                        bad("too many chunks for a Fixed Array index; \
+                             use larger chunks or an unlimited dimension")
+                    })?;
+                // A Single Chunk index needs that one chunk to exist; an
+                // empty dataset gets an all-unallocated Fixed Array instead.
+                let empty = shape.contains(&0);
+                if nslots == 1 && !empty {
+                    Ok(Self::SingleChunk)
+                } else {
+                    let grid = ChunkGrid::fixed_array(shape, Some(max), chunk_dims)?;
+                    Ok(Self::FixedArray(grid, nslots as usize))
+                }
+            }
+            1 => Ok(Self::ExtensibleArray(ChunkGrid::extensible_array(
+                shape,
+                Some(max),
+                chunk_dims,
+            )?)),
+            _ => Ok(Self::BTreeV2),
+        }
+    }
+}
+
+/// Place each written chunk at its linear index in `grid`. `chunks` are in
+/// row-major order over the chunks of the current extent (`split_into_chunks`).
+/// `len` fixes the slot count (Fixed Array); otherwise it is one past the
+/// highest index used.
+fn index_slots(
+    grid: &ChunkGrid,
+    shape: &[u64],
+    chunk_dims: &[u64],
+    chunks: &[WrittenChunk],
+    len: Option<usize>,
+) -> Result<Vec<Option<WrittenChunk>>, FormatError> {
+    let mut placed: Vec<(usize, &WrittenChunk)> = Vec::with_capacity(chunks.len());
+    for (i, chunk) in chunks.iter().enumerate() {
+        let scaled = scaled_coords(shape, chunk_dims, i);
+        let idx = usize::try_from(grid.linear_index(&scaled))
+            .map_err(|_| FormatError::Overflow("chunk index slot".into()))?;
+        placed.push((idx, chunk));
+    }
+    let n = len.unwrap_or_else(|| placed.iter().map(|&(i, _)| i + 1).max().unwrap_or(0));
+    let mut slots = vec![None; n];
+    for (idx, chunk) in placed {
+        *slots
+            .get_mut(idx)
+            .ok_or_else(|| FormatError::Overflow("chunk index slot".into()))? = Some(chunk.clone());
+    }
+    Ok(slots)
+}
+
+/// Scaled coordinates (`offset / chunk_dim`) of the `i`-th chunk in the
+/// row-major order `split_into_chunks` produces over the current extent.
+fn scaled_coords(shape: &[u64], chunk_dims: &[u64], i: usize) -> Vec<u64> {
+    let rank = shape.len();
+    let mut scaled = vec![0u64; rank];
+    let mut rem = i as u64;
+    for d in (0..rank).rev() {
+        let n = shape[d].div_ceil(chunk_dims[d]);
+        scaled[d] = rem % n;
+        rem /= n;
+    }
+    scaled
+}
+
+/// Node size the library gives a chunk index B-tree (`H5D_BT2_NODE_SIZE`),
+/// with its split and merge percentages.
+const BT2_NODE_SIZE: u32 = 2048;
+const BT2_SPLIT_PERCENT: u8 = 100;
+const BT2_MERGE_PERCENT: u8 = 40;
+/// B-tree v2 record types for chunk indexes (`H5B2_CDSET_ID`,
+/// `H5B2_CDSET_FILT_ID`).
+const BT2_CHUNK_UNFILTERED: u8 = 10;
+const BT2_CHUNK_FILTERED: u8 = 11;
+
+/// Build a version-2 B-tree chunk index (the library's index for datasets
+/// with more than one unlimited dimension) at a known absolute address.
+///
+/// `records` are `(scaled coordinates, chunk)` in lexicographic order of the
+/// coordinates, which is the order the library's comparator
+/// (`H5VM_vector_cmp_u`) keeps them in. The tree is a single leaf: the
+/// library's 2048-byte node when the records fit, otherwise a leaf node
+/// sized to hold them all (the root's record count is 16-bit, so at most
+/// 65535 chunks). Returns the bytes and the node size the layout message
+/// must record.
+fn build_btree_v2_chunk_index_at(
+    rank: usize,
+    records: &[(Vec<u64>, &WrittenChunk)],
+    offset_size: u8,
+    length_size: u8,
+    has_filters: bool,
+    base_address: u64,
+) -> Result<(Vec<u8>, u32), FormatError> {
+    let os = offset_size as usize;
+    let nrec = u16::try_from(records.len()).map_err(|_| {
+        FormatError::ChunkedReadError(
+            "more than 65535 chunks with more than one unlimited dimension: \
+             use larger chunks"
+                .into(),
+        )
+    })?;
+    let chunk_size_bytes = has_filters.then(|| {
+        let slots: Vec<Option<WrittenChunk>> =
+            records.iter().map(|(_, c)| Some((*c).clone())).collect();
+        filtered_chunk_size_len(&slots)
+    });
+    let record_size = os + chunk_size_bytes.map_or(0, |n| n + 4) + 8 * rank;
+    // Leaf: signature, version, type, records, checksum.
+    let leaf_len = 4 + 1 + 1 + records.len() * record_size + 4;
+    let node_size = u32::try_from(leaf_len)
+        .map_err(|_| FormatError::Overflow("B-tree v2 leaf size".into()))?
+        .max(BT2_NODE_SIZE);
+    let tree_type = if has_filters {
+        BT2_CHUNK_FILTERED
+    } else {
+        BT2_CHUNK_UNFILTERED
+    };
+
+    let hdr_len = 4 + 1 + 1 + 4 + 2 + 2 + 1 + 1 + os + 2 + length_size as usize + 4;
+    let leaf_address = base_address + hdr_len as u64;
+
+    let mut out = Vec::with_capacity(hdr_len + node_size as usize);
+    out.extend_from_slice(b"BTHD");
+    out.push(0); // version
+    out.push(tree_type);
+    out.extend_from_slice(&node_size.to_le_bytes());
+    out.extend_from_slice(&(record_size as u16).to_le_bytes());
+    out.extend_from_slice(&0u16.to_le_bytes()); // depth
+    out.push(BT2_SPLIT_PERCENT);
+    out.push(BT2_MERGE_PERCENT);
+    if records.is_empty() {
+        out.extend(core::iter::repeat_n(0xFF, os));
+    } else {
+        push_addr(&mut out, leaf_address, offset_size);
+    }
+    out.extend_from_slice(&nrec.to_le_bytes());
+    match length_size {
+        4 => out.extend_from_slice(&(records.len() as u32).to_le_bytes()),
+        _ => out.extend_from_slice(&(records.len() as u64).to_le_bytes()),
+    }
+    let sum = jenkins_lookup3(&out);
+    out.extend_from_slice(&sum.to_le_bytes());
+    debug_assert_eq!(out.len(), hdr_len);
+    if records.is_empty() {
+        return Ok((out, node_size));
+    }
+
+    let leaf_start = out.len();
+    out.extend_from_slice(b"BTLF");
+    out.push(0); // version
+    out.push(tree_type);
+    for (scaled, chunk) in records {
+        push_index_element(&mut out, Some(chunk), offset_size, chunk_size_bytes);
+        for &c in scaled {
+            out.extend_from_slice(&c.to_le_bytes());
+        }
+    }
+    let sum = jenkins_lookup3(&out[leaf_start..]);
+    out.extend_from_slice(&sum.to_le_bytes());
+    // The library reads whole nodes; pad the leaf out to the node size.
+    out.resize(leaf_start + node_size as usize, 0);
+    Ok((out, node_size))
+}
+
+/// Serialize a v4 layout message for a version-2 B-tree chunk index.
+fn serialize_v4_btree_v2(
+    chunk_dims: &[u32],
+    btree_address: u64,
+    offset_size: u8,
+    element_size: u32,
+    node_size: u32,
+) -> Vec<u8> {
+    let mut buf = layout_v4_chunked_prefix(chunk_dims, element_size);
+    buf.push(5); // chunk index type = 5 (version-2 B-tree)
+    buf.extend_from_slice(&node_size.to_le_bytes());
+    buf.push(BT2_SPLIT_PERCENT);
+    buf.push(BT2_MERGE_PERCENT);
+    push_addr(&mut buf, btree_address, offset_size);
+    buf
 }
 
 /// Build chunked data with absolute addresses.
@@ -790,11 +1238,7 @@ pub fn build_chunked_data_at_ext(
     maxshape: Option<&[u64]>,
 ) -> Result<ChunkedDataResult, FormatError> {
     let pre = precompress_chunks(raw_data, shape, chunk_dims, element_size, options)?;
-    Ok(build_chunked_data_from_precompressed(
-        &pre,
-        base_address,
-        maxshape,
-    ))
+    build_chunked_data_from_precompressed(&pre, base_address, maxshape)
 }
 
 /// Write selected elements into an existing in-memory dataset buffer.
@@ -1273,6 +1717,35 @@ mod tests {
         assert_eq!(pl.filters[1].client_data, vec![3]);
     }
 
+    #[test]
+    fn chunk_options_pipeline_lzf() {
+        let options = ChunkOptions {
+            plugin: Some(PluginFilter::Lzf),
+            ..Default::default()
+        };
+        assert!(options.is_chunked());
+        let pl = options.build_pipeline_for_chunk(8, 800).unwrap();
+        assert_eq!(pl.filters.len(), 2);
+        assert_eq!(pl.filters[0].filter_id, FILTER_SHUFFLE);
+        assert_eq!(pl.filters[1].filter_id, FILTER_LZF);
+        assert_eq!(pl.filters[1].client_data, vec![4, 0x0105, 800]);
+    }
+
+    #[test]
+    fn chunk_options_pipeline_bitshuffle_has_no_auto_shuffle() {
+        let options = ChunkOptions {
+            plugin: Some(PluginFilter::Bitshuffle {
+                block_size: 0,
+                compression: BitshuffleCompression::Zstd { level: 5 },
+            }),
+            ..Default::default()
+        };
+        let pl = options.build_pipeline(4).unwrap();
+        assert_eq!(pl.filters.len(), 1);
+        assert_eq!(pl.filters[0].filter_id, FILTER_BITSHUFFLE);
+        assert_eq!(pl.filters[0].client_data, vec![0, 4, 4, 0, 3, 5]);
+    }
+
     #[test]
     fn chunk_options_zstd_priority_over_deflate() {
         let options = ChunkOptions {
@@ -1314,6 +1787,7 @@ mod tests {
                 chunk_index_type,
                 single_chunk_filtered_size,
                 single_chunk_filter_mask,
+                ..
             } => {
                 assert_eq!(version, 4);
                 assert_eq!(chunk_index_type, Some(1));
@@ -1382,7 +1856,8 @@ mod tests {
                 filter_mask: 0,
             },
         ];
-        let fa = build_fixed_array_at(&chunks, 8, 8, false, 0x2000);
+        let slots: Vec<_> = chunks.into_iter().map(Some).collect();
+        let fa = build_fixed_array_at(&slots, 8, 8, false, 0x2000);
         // Should start with FAHD
         assert_eq!(&fa[0..4], b"FAHD");
         // FAHD size = 4+1+1+1+1+8+8+4 = 28
@@ -1429,7 +1904,8 @@ mod tests {
                 filter_mask: 0,
             },
         ];
-        let ea = ea_writer::build_extensible_array_at(&chunks, 8, 8, false, 0x2000);
+        let slots: Vec<_> = chunks.into_iter().map(Some).collect();
+        let ea = ea_writer::build_extensible_array_at(&slots, 8, 8, false, 0x2000);
         assert_eq!(&ea[0..4], b"EAHD");
         // Find EAIB after EAHD: 12 fixed + 6*8 stats + 8 addr + 4 checksum = 72
         let aehd_size = 4 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 6 * 8 + 8 + 4;

crates/clawhdf5-format/src/data_layout.rs

@@ -1,7 +1,7 @@
 //! HDF5 Data Layout message parsing (message type 0x0008).
 
 #[cfg(not(feature = "std"))]
-use alloc::{string::String, vec::Vec};
+use alloc::{format, string::String, vec::Vec};
 
 #[cfg(feature = "std")]
 use std::string::String;
@@ -24,6 +24,34 @@ pub struct VdsMapping {
     pub virtual_selection: Vec<u8>,
 }
 
+/// Most dimensions a layout message can list (libhdf5 `H5O_LAYOUT_NDIMS`):
+/// 32 dataspace dimensions plus the element size.
+const MAX_LAYOUT_NDIMS: usize = 33;
+
+/// libhdf5's checks on a chunked layout message's dimensions
+/// (`H5O__layout_decode`): at most [`MAX_LAYOUT_NDIMS`], no dimension 0, and
+/// before version 4 at least one dataspace dimension plus the element size.
+/// A zero chunk dimension used to read the dataset as all fill values.
+fn check_chunk_dims(dims: Vec<u32>, layout_version: u8) -> Result<Vec<u32>, FormatError> {
+    if dims.len() > MAX_LAYOUT_NDIMS {
+        return Err(FormatError::InvalidChunkDimensions(
+            "dimensionality is too large".into(),
+        ));
+    }
+    if layout_version < 4 && dims.len() < 2 {
+        return Err(FormatError::InvalidChunkDimensions(
+            "bad dimensions for chunked storage".into(),
+        ));
+    }
+    if let Some(u) = dims.iter().position(|&d| d == 0) {
+        return Err(FormatError::InvalidChunkDimensions(format!(
+            "bad chunk dimension value when parsing layout message - chunk dimension must be \
+             positive: mesg->u.chunk.dim[{u}] = 0"
+        )));
+    }
+    Ok(dims)
+}
+
 /// Parsed HDF5 data layout message.
 #[derive(Debug, Clone, PartialEq)]
 pub enum DataLayout {
@@ -45,7 +73,9 @@ pub enum DataLayout {
         chunk_dimensions: Vec<u32>,
         /// B-tree address, or `None` if undefined.
         btree_address: Option<u64>,
-        /// Layout version (3 or 4).
+        /// Layout version (3 or 4). Version 1/2 messages (HDF5 1.4/1.6-era)
+        /// use the same version-1 B-tree chunk index as version 3 and are
+        /// reported as 3.
         version: u8,
         /// Chunk index type (v4 only).
         chunk_index_type: Option<u8>,
@@ -53,6 +83,11 @@ pub enum DataLayout {
         single_chunk_filtered_size: Option<u64>,
         /// Filter mask for v4 single chunk with filters.
         single_chunk_filter_mask: Option<u32>,
+        /// Layout v4 flag bit 0 (`H5D_CHUNK_DONT_FILTER_PARTIAL_CHUNKS`):
+        /// partial edge chunks — those extending past the dataset's current
+        /// extent in some dimension — are stored without the filter pipeline,
+        /// even though their filter mask is 0. Always `false` for v3.
+        dont_filter_partial_edge_chunks: bool,
     },
     /// Virtual dataset layout (v4 only).
     Virtual {
@@ -67,21 +102,33 @@ pub enum DataLayout {
     },
 }
 
+/// Version-1 VDS mapping flag: the source file name is stored by an earlier
+/// entry, whose index follows in place of the name.
+const VDS_SOURCE_FILE_SHARED: u8 = 0x01;
+/// Version-1 VDS mapping flag: likewise for the source dataset name.
+const VDS_SOURCE_DSET_SHARED: u8 = 0x02;
+/// Version-1 VDS mapping flag: the source is in the virtual file itself
+/// (`"."`); no file name is stored.
+const VDS_SOURCE_SAME_FILE: u8 = 0x04;
+const VDS_ALL_FLAGS: u8 = VDS_SOURCE_FILE_SHARED | VDS_SOURCE_DSET_SHARED | VDS_SOURCE_SAME_FILE;
+
 /// Parse VDS mappings from global-heap object data.
 ///
 /// The global-heap block holding a VDS mapping list is laid out as
-/// (reverse-engineered and validated against HDF5 2.0):
+/// (`H5D__virtual_store_layout` / `H5D__virtual_load_layout` in libhdf5):
 ///
 /// ```text
 /// version(1) · nused(length_size, LE) · entry[nused] · checksum(4)
 /// ```
 ///
 /// Each entry is:
-/// - source file name — a null-terminated string in **block version 0**; in
-///   **block version 1** a same-file reference is encoded as a single `0x04`
-///   marker byte (the source file is the virtual file itself) in place of the
-///   name;
-/// - source dataset name (null-terminated string);
+/// - **block version 1 only:** a flags byte. `0x04`: the source is in the
+///   virtual file itself and no file name is stored; `0x01`/`0x02`: the
+///   source file/dataset name is that of an earlier entry, whose index
+///   (`length_size` bytes) is stored instead of the name. libhdf5 2.0 writes
+///   version 1 when the file's low version bound is 2.0 and it saves space;
+/// - source file name (null-terminated string, unless flagged above);
+/// - source dataset name (null-terminated string, unless flagged above);
 /// - source selection (serialized `H5S` dataspace selection — self-describing
 ///   in length);
 /// - virtual selection (serialized `H5S` dataspace selection).
@@ -107,7 +154,7 @@ pub fn parse_vds_mappings(
     // `nused` is untrusted; don't pre-allocate from it. Each entry consumes at
     // least a few bytes, so the loop is naturally bounded by the heap data and
     // a bogus `nused` simply errors out on the first short read.
-    let mut mappings = Vec::new();
+    let mut mappings: Vec<VdsMapping> = Vec::new();
     // Reads one self-describing selection at `pos`, returning its raw bytes and
     // advancing past it — bounds-checked so a corrupt selection can't overrun.
     let read_selection = |heap_data: &[u8], pos: &mut usize| -> Result<Vec<u8>, FormatError> {
@@ -127,17 +174,57 @@ pub fn parse_vds_mappings(
         Ok(bytes)
     };
 
-    for _ in 0..nused {
-        // Source file name (with the version-1 same-file marker handled).
-        let source_file = if version >= 1 && heap_data.get(pos) == Some(&0x04) {
+    if version > 1 {
+        return Err(FormatError::ChunkedReadError(
+            "unsupported VDS mapping block version".into(),
+        ));
+    }
+    for i in 0..nused {
+        // Version 1 prefixes each entry with a flags byte; a name may then be
+        // omitted (same file) or replaced by the index of an earlier entry
+        // holding the same name (`H5D__virtual_load_layout`).
+        let flags = if version >= 1 {
+            let f = *heap_data.get(pos).ok_or(FormatError::UnexpectedEof {
+                expected: pos + 1,
+                available: heap_data.len(),
+            })?;
             pos += 1;
+            if f & !VDS_ALL_FLAGS != 0 {
+                return Err(FormatError::ChunkedReadError(
+                    "unknown VDS mapping flags".into(),
+                ));
+            }
+            f
+        } else {
+            0
+        };
+        // Index of an earlier entry, for a shared name.
+        let earlier = |pos: &mut usize| -> Result<usize, FormatError> {
+            let idx = read_length(heap_data, *pos, length_size)?;
+            *pos += ls;
+            if idx >= i {
+                return Err(FormatError::ChunkedReadError(
+                    "VDS mapping shares a name with a later entry".into(),
+                ));
+            }
+            Ok(idx as usize)
+        };
+
+        let source_file = if flags & VDS_SOURCE_SAME_FILE != 0 {
             String::from(".")
+        } else if flags & VDS_SOURCE_FILE_SHARED != 0 {
+            let idx = earlier(&mut pos)?;
+            mappings[idx].source_file.clone()
         } else {
             read_null_terminated_string(heap_data, &mut pos)?
         };
 
-        // Source dataset name.
-        let source_dataset = read_null_terminated_string(heap_data, &mut pos)?;
+        let source_dataset = if flags & VDS_SOURCE_DSET_SHARED != 0 {
+            let idx = earlier(&mut pos)?;
+            mappings[idx].source_dataset.clone()
+        } else {
+            read_null_terminated_string(heap_data, &mut pos)?
+        };
 
         // Source selection, then virtual selection (both self-describing length).
         let source_selection = read_selection(heap_data, &mut pos)?;
@@ -256,6 +343,7 @@ impl DataLayout {
         let layout_class = data[1];
 
         match version {
+            1 | 2 => Self::parse_v1_v2(data, offset_size),
             3 => Self::parse_v3(data, layout_class, offset_size, length_size),
             // v5 (emitted by HDF5 1.14+/2.0 with `libver=latest`) uses the same
             // message structure as v4 — only the version number was bumped.
@@ -264,6 +352,87 @@ impl DataLayout {
         }
     }
 
+    /// Layout message versions 1 and 2 (HDF5 before 1.6.3):
+    ///
+    /// ```text
+    /// version(1) · dimensionality(1) · layout class(1) · reserved(5)
+    /// · address(offset_size)      — contiguous and chunked only
+    /// · dimension sizes(4 × dimensionality)
+    /// · compact data size(4) · compact raw data — compact only
+    /// ```
+    ///
+    /// The dimension sizes are the dataset's (contiguous/compact) or the
+    /// chunk's (chunked) extent plus a trailing element-size dimension, as in
+    /// version 3's chunked form. libhdf5 ignores them for contiguous storage
+    /// and sizes the data from the dataspace; the product of the stored
+    /// dimensions is that same size, and a disagreement (a dimension that was
+    /// truncated to 32 bits) is caught by the reader's size check rather than
+    /// returning wrong data.
+    fn parse_v1_v2(data: &[u8], offset_size: u8) -> Result<DataLayout, FormatError> {
+        ensure_len(data, 0, 8)?;
+        let dimensionality = data[1] as usize;
+        let layout_class = data[2];
+        // H5O_LAYOUT_NDIMS: 32 dataspace dimensions + the element-size one.
+        if dimensionality > 33 {
+            return Err(FormatError::Overflow(format!(
+                "data layout dimensionality {dimensionality} exceeds 33"
+            )));
+        }
+        let mut p = 8;
+        let os = offset_size as usize;
+        let address = match layout_class {
+            1 | 2 => {
+                ensure_len(data, p, os)?;
+                let a = if is_undefined(data, p, offset_size) {
+                    None
+                } else {
+                    Some(read_offset(data, p, offset_size)?)
+                };
+                p += os;
+                a
+            }
+            0 => None,
+            _ => return Err(FormatError::InvalidLayoutClass(layout_class)),
+        };
+        ensure_len(data, p, dimensionality * 4)?;
+        let dims: Vec<u32> = data[p..p + dimensionality * 4]
+            .as_chunks::<4>()
+            .0
+            .iter()
+            .map(|c| u32::from_le_bytes(*c))
+            .collect();
+        p += dimensionality * 4;
+        match layout_class {
+            0 => {
+                ensure_len(data, p, 4)?;
+                let size =
+                    u32::from_le_bytes([data[p], data[p + 1], data[p + 2], data[p + 3]]) as usize;
+                ensure_len(data, p + 4, size)?;
+                Ok(DataLayout::Compact {
+                    data: data[p + 4..p + 4 + size].to_vec(),
+                })
+            }
+            1 => {
+                let size = dims
+                    .iter()
+                    .try_fold(1u64, |acc, &d| acc.checked_mul(d as u64))
+                    .ok_or_else(|| {
+                        FormatError::Overflow(format!("contiguous layout size {dims:?}"))
+                    })?;
+                Ok(DataLayout::Contiguous { address, size })
+            }
+            _ => Ok(DataLayout::Chunked {
+                chunk_dimensions: check_chunk_dims(dims, 2)?,
+                btree_address: address,
+                version: 3,
+                chunk_index_type: None,
+                single_chunk_filtered_size: None,
+                single_chunk_filter_mask: None,
+                dont_filter_partial_edge_chunks: false,
+            }),
+        }
+    }
+
     fn parse_v3(
         data: &[u8],
         layout_class: u8,
@@ -316,12 +485,13 @@ impl DataLayout {
                     p += 4;
                 }
                 Ok(DataLayout::Chunked {
-                    chunk_dimensions,
+                    chunk_dimensions: check_chunk_dims(chunk_dimensions, 3)?,
                     btree_address,
                     version: 3,
                     chunk_index_type: None,
                     single_chunk_filtered_size: None,
                     single_chunk_filter_mask: None,
+                    dont_filter_partial_edge_chunks: false,
                 })
             }
             _ => Err(FormatError::InvalidLayoutClass(layout_class)),
@@ -364,47 +534,40 @@ impl DataLayout {
                 let dimensionality = data[pos + 1] as usize;
                 let dim_size_encoded_length = data[pos + 2] as usize;
                 let mut p = pos + 3;
+                if dimensionality > MAX_LAYOUT_NDIMS {
+                    return Err(FormatError::InvalidChunkDimensions(
+                        "dimensionality is too large".into(),
+                    ));
+                }
 
-                // dimension sizes
+                // Each dimension takes 1 to 8 bytes (libhdf5 writes the
+                // fewest that hold the largest one, so 3, 5, 6 and 7 occur:
+                // a chunk dimension of 70 000 takes 3). libhdf5 refuses 0
+                // and more than 8.
+                if dim_size_encoded_length == 0 || dim_size_encoded_length > 8 {
+                    return Err(FormatError::InvalidChunkDimensions(
+                        "encoded chunk dimension size is too large".into(),
+                    ));
+                }
                 ensure_len(data, p, dimensionality * dim_size_encoded_length)?;
                 let mut chunk_dimensions = Vec::with_capacity(dimensionality);
                 for _ in 0..dimensionality {
-                    let val = match dim_size_encoded_length {
-                        1 => data[p] as u32,
-                        2 => u16::from_le_bytes([data[p], data[p + 1]]) as u32,
-                        4 => u32::from_le_bytes([data[p], data[p + 1], data[p + 2], data[p + 3]]),
-                        8 => {
-                            // V4 chunked encodes dimension sizes as 8 bytes, but
-                            // our ChunkedStorageV4 stores them as u32. We read only
-                            // the low 4 bytes (little-endian). This silently
-                            // truncates dimensions > 4 GiB, which are not expected
-                            // in practice (HDF5 chunk dimensions are always small).
-                            // If the high bytes are non-zero, the file is malformed
-                            // or uses dimensions we cannot represent.
-                            let high = u32::from_le_bytes([
-                                data[p + 4],
-                                data[p + 5],
-                                data[p + 6],
-                                data[p + 7],
-                            ]);
-                            if high != 0 {
-                                return Err(FormatError::UnexpectedEof {
-                                    expected: p + 8,
-                                    available: data.len(),
-                                });
-                            }
-                            u32::from_le_bytes([data[p], data[p + 1], data[p + 2], data[p + 3]])
-                        }
-                        _ => {
-                            return Err(FormatError::UnexpectedEof {
-                                expected: p + dim_size_encoded_length,
-                                available: data.len(),
-                            });
-                        }
-                    };
+                    let val = data[p..p + dim_size_encoded_length]
+                        .iter()
+                        .rev()
+                        .fold(0u64, |acc, &b| (acc << 8) | u64::from(b));
+                    // Chunk dimensions are held as u32; HDF5 2.0 can write
+                    // larger ones (layout version 5), which are refused
+                    // rather than truncated.
+                    let val = u32::try_from(val).map_err(|_| {
+                        FormatError::InvalidChunkDimensions(format!(
+                            "chunk dimension {val} is larger than 2^32 - 1, which is not supported"
+                        ))
+                    })?;
                     chunk_dimensions.push(val);
                     p += dim_size_encoded_length;
                 }
+                let chunk_dimensions = check_chunk_dims(chunk_dimensions, 4)?;
 
                 // chunk index type
                 ensure_len(data, p, 1)?;
@@ -505,6 +668,7 @@ impl DataLayout {
                     chunk_index_type: Some(chunk_index_type),
                     single_chunk_filtered_size,
                     single_chunk_filter_mask,
+                    dont_filter_partial_edge_chunks: flags & 0x01 != 0,
                 })
             }
             3 => {
@@ -539,6 +703,202 @@ impl DataLayout {
 mod tests {
     use super::*;
 
+    /// Version 1/2 header: version, dimensionality, class, reserved(5).
+    fn v1v2_header(version: u8, ndims: u8, class: u8) -> Vec<u8> {
+        vec![version, ndims, class, 0, 0, 0, 0, 0]
+    }
+
+    #[test]
+    fn v2_compact() {
+        let mut buf = v1v2_header(2, 2, 0);
+        // dims (3 elements of 2 bytes) — no address for compact
+        buf.extend_from_slice(&3u32.to_le_bytes());
+        buf.extend_from_slice(&2u32.to_le_bytes());
+        buf.extend_from_slice(&6u32.to_le_bytes()); // compact size (u32 in v1/v2)
+        buf.extend_from_slice(&[1, 0, 2, 0, 3, 0]);
+        assert_eq!(
+            DataLayout::parse(&buf, 8, 8).unwrap(),
+            DataLayout::Compact {
+                data: vec![1, 0, 2, 0, 3, 0]
+            }
+        );
+    }
+
+    #[test]
+    fn v1_contiguous_size_from_dimensions() {
+        let mut buf = v1v2_header(1, 3, 1);
+        buf.extend_from_slice(&0x800u32.to_le_bytes()); // 4-byte address
+        for d in [10u32, 20, 4] {
+            buf.extend_from_slice(&d.to_le_bytes());
+        }
+        assert_eq!(
+            DataLayout::parse(&buf, 4, 4).unwrap(),
+            DataLayout::Contiguous {
+                address: Some(0x800),
+                size: 800,
+            }
+        );
+    }
+
+    #[test]
+    fn v1_contiguous_undefined_address() {
+        let mut buf = v1v2_header(1, 2, 1);
+        buf.extend_from_slice(&[0xFF; 8]);
+        buf.extend_from_slice(&5u32.to_le_bytes());
+        buf.extend_from_slice(&8u32.to_le_bytes());
+        assert_eq!(
+            DataLayout::parse(&buf, 8, 8).unwrap(),
+            DataLayout::Contiguous {
+                address: None,
+                size: 40,
+            }
+        );
+    }
+
+    #[test]
+    fn v1_chunked_maps_to_btree_v1_index() {
+        let mut buf = v1v2_header(1, 3, 2);
+        buf.extend_from_slice(&0x1234u64.to_le_bytes());
+        for d in [50u32, 50, 4] {
+            buf.extend_from_slice(&d.to_le_bytes());
+        }
+        assert_eq!(
+            DataLayout::parse(&buf, 8, 8).unwrap(),
+            DataLayout::Chunked {
+                chunk_dimensions: vec![50, 50, 4],
+                btree_address: Some(0x1234),
+                version: 3,
+                chunk_index_type: None,
+                single_chunk_filtered_size: None,
+                single_chunk_filter_mask: None,
+                dont_filter_partial_edge_chunks: false,
+            }
+        );
+    }
+
+    /// A v3 chunked layout message with these dims (element size last).
+    fn v3_chunked_msg(dims: &[u32]) -> Vec<u8> {
+        let mut buf = vec![3u8, 2, dims.len() as u8];
+        buf.extend_from_slice(&0x1000u64.to_le_bytes());
+        for d in dims {
+            buf.extend_from_slice(&d.to_le_bytes());
+        }
+        buf
+    }
+
+    #[test]
+    fn chunk_dimensions_are_checked_when_the_layout_is_parsed() {
+        assert!(DataLayout::parse(&v3_chunked_msg(&[4, 4, 8]), 8, 8).is_ok());
+        // A zero chunk dimension used to read as all fill values.
+        let err = DataLayout::parse(&v3_chunked_msg(&[4, 0, 8]), 8, 8).unwrap_err();
+        assert!(
+            matches!(&err, FormatError::InvalidChunkDimensions(m) if m.contains("dim[1] = 0")),
+            "{err:?}"
+        );
+        // Only the element-size dimension: libhdf5 "bad dimensions".
+        assert_eq!(
+            DataLayout::parse(&v3_chunked_msg(&[8]), 8, 8).unwrap_err(),
+            FormatError::InvalidChunkDimensions("bad dimensions for chunked storage".into())
+        );
+        assert_eq!(
+            DataLayout::parse(&v3_chunked_msg(&[1; 34]), 8, 8).unwrap_err(),
+            FormatError::InvalidChunkDimensions("dimensionality is too large".into())
+        );
+        // v1/v2 and v4 messages get the zero check too.
+        let mut v1 = v1v2_header(1, 2, 2);
+        v1.extend_from_slice(&0x1000u64.to_le_bytes());
+        v1.extend_from_slice(&0u32.to_le_bytes());
+        v1.extend_from_slice(&8u32.to_le_bytes());
+        assert!(matches!(
+            DataLayout::parse(&v1, 8, 8),
+            Err(FormatError::InvalidChunkDimensions(_))
+        ));
+        let mut v4 = vec![4u8, 2, 0, 2, 4];
+        v4.extend_from_slice(&0u32.to_le_bytes());
+        v4.extend_from_slice(&8u32.to_le_bytes());
+        v4.push(3); // fixed array index
+        v4.push(0); // page bits
+        v4.extend_from_slice(&0x1000u64.to_le_bytes());
+        assert!(matches!(
+            DataLayout::parse(&v4, 8, 8),
+            Err(FormatError::InvalidChunkDimensions(_))
+        ));
+    }
+
+    /// A v4 chunked layout (fixed array index) whose `dims` are each
+    /// encoded in `width` bytes.
+    fn v4_chunked_msg(width: u8, dims: &[u64]) -> Vec<u8> {
+        let mut m = vec![4u8, 2, 0, dims.len() as u8, width];
+        for &d in dims {
+            m.extend_from_slice(&d.to_le_bytes()[..width.min(8) as usize]);
+        }
+        m.push(3); // fixed array index
+        m.push(0); // page bits
+        m.extend_from_slice(&0x1000u64.to_le_bytes());
+        m
+    }
+
+    #[test]
+    fn v4_chunk_dimensions_take_1_to_8_bytes() {
+        // libhdf5 encodes each dimension in the fewest bytes that hold the
+        // largest: a chunk dimension of 70 000 takes 3, and 3, 5, 6 and 7
+        // were refused ("UnexpectedEof").
+        for width in 1..=8u8 {
+            let dims = [if width >= 3 { 70_000 } else { 200 }, 8];
+            let layout = DataLayout::parse(&v4_chunked_msg(width, &dims), 8, 8)
+                .unwrap_or_else(|e| panic!("width {width}: {e:?}"));
+            assert!(
+                matches!(&layout, DataLayout::Chunked { chunk_dimensions, .. }
+                    if chunk_dimensions.iter().map(|&d| u64::from(d)).eq(dims)),
+                "width {width}: {layout:?}"
+            );
+        }
+        // libhdf5 refuses 0 and more than 8 bytes.
+        for width in [0u8, 9] {
+            assert_eq!(
+                DataLayout::parse(&v4_chunked_msg(width, &[4, 8]), 8, 8).unwrap_err(),
+                FormatError::InvalidChunkDimensions(
+                    "encoded chunk dimension size is too large".into()
+                )
+            );
+        }
+        // A dimension past u32 cannot be represented and is refused, not
+        // truncated.
+        assert!(matches!(
+            DataLayout::parse(&v4_chunked_msg(5, &[1 << 32, 8]), 8, 8),
+            Err(FormatError::InvalidChunkDimensions(m)) if m.contains("2^32")
+        ));
+    }
+
+    #[test]
+    fn v1v2_rejects_bad_class_dimensionality_and_truncation() {
+        assert_eq!(
+            DataLayout::parse(&v1v2_header(1, 1, 3), 8, 8).unwrap_err(),
+            FormatError::InvalidLayoutClass(3)
+        );
+        assert!(matches!(
+            DataLayout::parse(&v1v2_header(2, 34, 1), 8, 8).unwrap_err(),
+            FormatError::Overflow(_)
+        ));
+        // Chunked, dims cut short.
+        let mut buf = v1v2_header(1, 2, 2);
+        buf.extend_from_slice(&0x10u64.to_le_bytes());
+        buf.extend_from_slice(&7u32.to_le_bytes());
+        assert!(matches!(
+            DataLayout::parse(&buf, 8, 8).unwrap_err(),
+            FormatError::UnexpectedEof { .. }
+        ));
+        // Compact, raw data shorter than its declared size.
+        let mut buf = v1v2_header(2, 1, 0);
+        buf.extend_from_slice(&4u32.to_le_bytes());
+        buf.extend_from_slice(&100u32.to_le_bytes());
+        buf.extend_from_slice(&[0; 4]);
+        assert!(matches!(
+            DataLayout::parse(&buf, 8, 8).unwrap_err(),
+            FormatError::UnexpectedEof { .. }
+        ));
+    }
+
     #[test]
     fn v3_compact() {
         let mut buf = vec![3u8, 0]; // version=3, class=0 (compact)
@@ -602,6 +962,7 @@ mod tests {
                 chunk_index_type: None,
                 single_chunk_filtered_size: None,
                 single_chunk_filter_mask: None,
+                dont_filter_partial_edge_chunks: false,
             }
         );
     }
@@ -679,10 +1040,35 @@ mod tests {
                 chunk_index_type: Some(1),
                 single_chunk_filtered_size: None,
                 single_chunk_filter_mask: None,
+                dont_filter_partial_edge_chunks: false,
             }
         );
     }
 
+    #[test]
+    fn v4_chunked_dont_filter_partial_edge_chunks_flag() {
+        let mut buf = vec![4u8, 2]; // version=4, class=2
+        buf.push(0x01); // flags bit 0 = don't filter partial edge chunks
+        buf.push(2); // dimensionality=2
+        buf.push(4); // dim_size_encoded_length=4
+        buf.extend_from_slice(&5u32.to_le_bytes());
+        buf.extend_from_slice(&4u32.to_le_bytes());
+        buf.push(3); // Fixed Array
+        buf.push(10); // max_dblk_page_nelmts_bits
+        buf.extend_from_slice(&0x3000u64.to_le_bytes());
+        match DataLayout::parse(&buf, 8, 8).unwrap() {
+            DataLayout::Chunked {
+                dont_filter_partial_edge_chunks,
+                btree_address,
+                ..
+            } => {
+                assert!(dont_filter_partial_edge_chunks);
+                assert_eq!(btree_address, Some(0x3000));
+            }
+            other => panic!("expected Chunked, got {other:?}"),
+        }
+    }
+
     #[test]
     fn v4_chunked_single_chunk_with_filters() {
         let mut buf = vec![4u8, 2]; // version=4, class=2
@@ -705,6 +1091,7 @@ mod tests {
                 chunk_index_type: Some(1),
                 single_chunk_filtered_size: Some(1024),
                 single_chunk_filter_mask: Some(0),
+                dont_filter_partial_edge_chunks: false,
             }
         );
     }
@@ -815,6 +1202,62 @@ mod tests {
         assert_eq!(v1.iter_linear_1d(8).unwrap(), vec![4, 5, 6, 7]);
     }
 
+    #[test]
+    fn parse_vds_mappings_v1_shared_names() {
+        // Written by HDF5 2.0 (h5py, libver=("v200", "v200")) for three
+        // mappings from `a_rather_long_source_file.h5:a_rather_long_dataset_name`
+        // and one from the same file: the entries carry flags 0x00, 0x03, 0x03
+        // and 0x06, so names after the first are stored as entry indices.
+        let blob: &[u8] = &[
+            0x01, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x61, 0x5f, 0x72, 0x61,
+            0x74, 0x68, 0x65, 0x72, 0x5f, 0x6c, 0x6f, 0x6e, 0x67, 0x5f, 0x73, 0x6f, 0x75, 0x72,
+            0x63, 0x65, 0x5f, 0x66, 0x69, 0x6c, 0x65, 0x2e, 0x68, 0x35, 0x00, 0x61, 0x5f, 0x72,
+            0x61, 0x74, 0x68, 0x65, 0x72, 0x5f, 0x6c, 0x6f, 0x6e, 0x67, 0x5f, 0x64, 0x61, 0x74,
+            0x61, 0x73, 0x65, 0x74, 0x5f, 0x6e, 0x61, 0x6d, 0x65, 0x00, 0x02, 0x00, 0x00, 0x00,
+            0x03, 0x00, 0x00, 0x00, 0x01, 0x02, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
+            0x01, 0x00, 0x04, 0x00, 0x02, 0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x01, 0x02,
+            0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00,
+            0x01, 0x00, 0x01, 0x00, 0x04, 0x00, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x03,
+            0x00, 0x00, 0x00, 0x01, 0x02, 0x01, 0x00, 0x00, 0x00, 0x04, 0x00, 0x01, 0x00, 0x01,
+            0x00, 0x04, 0x00, 0x02, 0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x01, 0x02, 0x02,
+            0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01,
+            0x00, 0x01, 0x00, 0x04, 0x00, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x03, 0x00,
+            0x00, 0x00, 0x01, 0x02, 0x01, 0x00, 0x00, 0x00, 0x08, 0x00, 0x01, 0x00, 0x01, 0x00,
+            0x04, 0x00, 0x02, 0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x01, 0x02, 0x02, 0x00,
+            0x00, 0x00, 0x02, 0x00, 0x01, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00,
+            0x01, 0x00, 0x04, 0x00, 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02,
+            0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x01, 0x02, 0x01, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x01, 0x00, 0x01, 0x00, 0x04, 0x00, 0x02, 0x00, 0x00, 0x00, 0x03, 0x00, 0x00,
+            0x00, 0x01, 0x02, 0x02, 0x00, 0x00, 0x00, 0x03, 0x00, 0x01, 0x00, 0x01, 0x00, 0x01,
+            0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x04, 0x00, 0x8e, 0xa7, 0xea, 0x7a,
+        ];
+        let mappings = parse_vds_mappings(blob, 8).unwrap();
+        let names: Vec<(&str, &str)> = mappings
+            .iter()
+            .map(|m| (m.source_file.as_str(), m.source_dataset.as_str()))
+            .collect();
+        let (file, dset) = ("a_rather_long_source_file.h5", "a_rather_long_dataset_name");
+        assert_eq!(
+            names,
+            vec![(file, dset), (file, dset), (file, dset), (".", dset)]
+        );
+    }
+
+    #[test]
+    fn parse_vds_mappings_v1_forward_reference_is_error() {
+        // Entry 0 claiming to share entry 0's file name must not index past
+        // the entries decoded so far.
+        let mut blob = vec![0x01u8, 1, 0, 0, 0, 0, 0, 0, 0, 0x01];
+        blob.extend_from_slice(&[0u8; 8]);
+        blob.extend_from_slice(b"d\0");
+        assert!(parse_vds_mappings(&blob, 8).is_err());
+        // Unknown flag bits are refused.
+        let blob = [0x01u8, 1, 0, 0, 0, 0, 0, 0, 0, 0x08, b'd', 0];
+        assert!(parse_vds_mappings(&blob, 8).is_err());
+    }
+
     #[test]
     fn parse_vds_mappings_external_v0() {
         // Block version 0 with an explicit (external) source file name.

crates/clawhdf5-format/src/ea_writer.rs

@@ -7,7 +7,9 @@ extern crate alloc;
 use alloc::{vec, vec::Vec};
 
 use crate::checksum::jenkins_lookup3;
-use crate::chunked_write::WrittenChunk;
+use crate::chunked_write::{
+    WrittenChunk, filtered_chunk_size_len, push_addr, push_index_element, push_v4_chunk_dims,
+};
 
 /// Serialize a v4 Extensible Array layout message.
 pub(crate) fn serialize_v4_extensible_array(
@@ -24,45 +26,17 @@ pub(crate) fn serialize_v4_extensible_array(
     let ndims = chunk_dims.len() as u8 + 1;
     buf.push(ndims);
 
-    let max_dim = chunk_dims
-        .iter()
-        .map(|&d| d as u64)
-        .chain(core::iter::once(element_size as u64))
-        .max()
-        .unwrap_or(1);
-    let dim_encoded_len: u8 = if max_dim <= 0xFF {
-        1
-    } else if max_dim <= 0xFFFF {
-        2
-    } else {
-        4
-    };
-    buf.push(dim_encoded_len);
-
-    for &d in chunk_dims {
-        match dim_encoded_len {
-            1 => buf.push(d as u8),
-            2 => buf.extend_from_slice(&(d as u16).to_le_bytes()),
-            4 => buf.extend_from_slice(&d.to_le_bytes()),
-            _ => unreachable!("unexpected dim_encoded_len: {dim_encoded_len}"),
-        }
-    }
-    match dim_encoded_len {
-        1 => buf.push(element_size as u8),
-        2 => buf.extend_from_slice(&(element_size as u16).to_le_bytes()),
-        4 => buf.extend_from_slice(&element_size.to_le_bytes()),
-        _ => unreachable!("unexpected dim_encoded_len: {dim_encoded_len}"),
-    }
+    push_v4_chunk_dims(&mut buf, chunk_dims, element_size);
 
     // chunk index type = 4 (Extensible Array)
     buf.push(4);
 
     // EA creation parameters (must match AEHD and HDF5 C library defaults)
-    buf.push(32); // max_nelmts_bits
-    buf.push(4); // idx_blk_elmts
-    buf.push(4); // super_blk_min_data_ptrs
-    buf.push(16); // data_blk_min_elmts
-    buf.push(10); // max_dblk_page_nelmts_bits
+    buf.push(MAX_NELMTS_BITS);
+    buf.push(IDX_BLK_ELMTS);
+    buf.push(SUP_BLK_MIN_DATA_PTRS);
+    buf.push(DATA_BLK_MIN_ELMTS);
+    buf.push(MAX_DBLK_PAGE_NELMTS_BITS);
 
     // EA header address
     match offset_size {
@@ -74,304 +48,281 @@ pub(crate) fn serialize_v4_extensible_array(
     buf
 }
 
+// EA creation parameters — the HDF5 library's defaults for chunk indexes
+// (`H5D_EARRAY_*`); the layout message above and the header must agree.
+const MAX_NELMTS_BITS: u8 = 32;
+const IDX_BLK_ELMTS: u8 = 4;
+const SUP_BLK_MIN_DATA_PTRS: u8 = 4;
+const DATA_BLK_MIN_ELMTS: u8 = 16;
+const MAX_DBLK_PAGE_NELMTS_BITS: u8 = 10;
+
+/// One data block of the array: its first element (relative to the end of
+/// the index block's own elements), element count, and address when it is
+/// allocated.
+struct DataBlock {
+    start: usize,
+    nelmts: usize,
+    addr: Option<u64>,
+}
+
 /// Build a complete Extensible Array at a known absolute address.
 ///
-/// For simplicity, we put all elements inline in the index block when the
-/// number of chunks is small (up to idx_blk_elmts), otherwise use inline +
-/// direct data blocks.
+/// `slots[i]` is the element at linear index `i` (see `chunk_grid`); `None`
+/// marks an unallocated chunk. The first `IDX_BLK_ELMTS` elements live in
+/// the index block, the rest in data blocks grouped by super block level
+/// exactly as `H5EA__hdr_init` sizes them: level `u` has `2^(u/2)` data
+/// blocks of `DATA_BLK_MIN_ELMTS * 2^ceil(u/2)` elements. The data blocks of
+/// the first levels are addressed straight from the index block; later
+/// levels go through a super block (EASB). Data blocks larger than a page
+/// (`2^MAX_DBLK_PAGE_NELMTS_BITS` elements) are paged, with their page-init
+/// bits kept in the owning super block. Only blocks holding a defined element
+/// are allocated; the rest keep the undefined address, as in a file the
+/// library wrote.
 pub fn build_extensible_array_at(
-    chunks: &[WrittenChunk],
+    slots: &[Option<WrittenChunk>],
     offset_size: u8,
     length_size: u8,
     has_filters: bool,
     ea_base_address: u64,
 ) -> Vec<u8> {
     let os = offset_size as usize;
-    let num_elements = chunks.len();
-
-    // Compute element encoding size (same logic as Fixed Array)
-    let chunk_size_bytes: usize = if has_filters {
-        let max_raw = chunks.iter().map(|c| c.raw_size).max().unwrap_or(1);
-        let log2_val = if max_raw <= 1 {
-            0
-        } else {
-            63 - max_raw.leading_zeros()
-        };
-        let len = 1 + ((log2_val + 8) / 8) as usize;
-        len.min(8)
-    } else {
-        0
-    };
-
-    let elem_size = if has_filters {
-        os + chunk_size_bytes + 4
-    } else {
-        os
-    };
-
+    let chunk_size_bytes = has_filters.then(|| filtered_chunk_size_len(slots));
+    let elem_size = os + chunk_size_bytes.map_or(0, |n| n + 4);
     let client_id: u8 = if has_filters { 1 } else { 0 };
+    let arr_off_size = (MAX_NELMTS_BITS as usize).div_ceil(8);
+    let page_nelmts = 1usize << MAX_DBLK_PAGE_NELMTS_BITS;
+    let idx_blk = IDX_BLK_ELMTS as usize;
 
-    // EA creation parameters — must match HDF5 C library defaults exactly
-    let max_nelmts_bits: u8 = 32;
-    let idx_blk_elmts: u8 = 4;
-    let min_dblk_nelmts: u8 = 16;
-    let super_blk_min_nelmts: u8 = 4;
-    let max_dblk_nelmts_bits: u8 = 10;
+    // Elements past the last defined one are never realised
+    // (`max_idx_set` is one past the highest index ever set).
+    let max_idx_set = slots.iter().rposition(Option::is_some).map_or(0, |i| i + 1);
+    let slots = &slots[..max_idx_set];
+    let defined_in = |start: usize, n: usize| -> bool {
+        let lo = idx_blk.saturating_add(start).min(slots.len());
+        let hi = idx_blk
+            .saturating_add(start)
+            .saturating_add(n)
+            .min(slots.len());
+        slots[lo..hi].iter().any(Option::is_some)
+    };
 
-    // EAHD size: fixed(12) + 6 stats(6*length_size) + addr(offset_size) + checksum(4)
+    // Super block levels: (ndblks, dblk_nelmts, first element).
+    let log2_dmin = (DATA_BLK_MIN_ELMTS as u32).trailing_zeros() as usize;
+    let nsblks = 1 + MAX_NELMTS_BITS as usize - log2_dmin;
+    let ndblk_addrs = 2 * (SUP_BLK_MIN_DATA_PTRS as usize - 1);
+    let mut levels: Vec<(usize, usize, usize)> = Vec::with_capacity(nsblks);
+    let mut start = 0usize;
+    for u in 0..nsblks {
+        let ndblks = 1usize << (u / 2);
+        let nelmts = (DATA_BLK_MIN_ELMTS as usize) << u.div_ceil(2);
+        levels.push((ndblks, nelmts, start));
+        // Saturate: on 32-bit targets the last levels only need to compare
+        // as "beyond the end".
+        start = start.saturating_add(ndblks.saturating_mul(nelmts));
+    }
+    // Levels whose data blocks the index block addresses directly.
+    let mut direct_levels = 0;
+    let mut n = 0;
+    while n < ndblk_addrs {
+        n += levels[direct_levels].0;
+        direct_levels += 1;
+    }
+    let nsblk_addrs = nsblks - direct_levels;
+
+    let dblk_size = |nelmts: usize| -> usize {
+        let prefix = 4 + 1 + 1 + os + arr_off_size + 4;
+        if nelmts > page_nelmts {
+            prefix + (nelmts / page_nelmts) * (page_nelmts * elem_size + 4)
+        } else {
+            prefix + nelmts * elem_size
+        }
+    };
+    let sblk_bitmap_len = |ndblks: usize, nelmts: usize| -> usize {
+        if nelmts > page_nelmts {
+            ndblks * (nelmts / page_nelmts).div_ceil(8)
+        } else {
+            0
+        }
+    };
+
+    // Plan addresses: header, index block, the direct data blocks, then each
+    // allocated super block followed by its allocated data blocks.
     let aehd_size = 4 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 6 * length_size as usize + os + 4;
     let aeib_address = ea_base_address + aehd_size as u64;
+    let aeib_size = 4 + 1 + 1 + os + idx_blk * elem_size + ndblk_addrs * os + nsblk_addrs * os + 4;
+    let mut cursor = aeib_address + aeib_size as u64;
 
-    // Determine how many elements go inline vs data blocks
-    let n_inline = (idx_blk_elmts as usize).min(num_elements);
-    let remaining_after_inline = num_elements.saturating_sub(n_inline);
+    let mut ndata_blks = 0u64;
+    let mut data_blk_size = 0u64;
+    let mut nsuper_blks = 0u64;
+    let mut super_blk_size = 0u64;
+    let mut realized = idx_blk as u64;
 
-    // Compute super block layout per HDF5 spec
-    let sblk_min = super_blk_min_nelmts as usize;
-    let log2_dblk_min = if min_dblk_nelmts <= 1 {
-        0
-    } else {
-        (min_dblk_nelmts as u32).trailing_zeros() as usize
-    };
-    let nsblks = (max_nelmts_bits as usize).saturating_sub(log2_dblk_min) + 1;
-
-    // Direct data block addresses (from super blocks 0..sblk_min-1)
-    let mut dblk_sizes: Vec<usize> = Vec::new();
-    for sblk_idx in 0..sblk_min.min(nsblks) {
-        let ndblks = 1usize << (sblk_idx / 2);
-        let dblk_nelmts = (min_dblk_nelmts as usize) * (1 << sblk_idx.div_ceil(2));
-        for _ in 0..ndblks {
-            dblk_sizes.push(dblk_nelmts);
+    let mut plan_dblk = |cursor: &mut u64, start: usize, nelmts: usize| -> DataBlock {
+        let addr = defined_in(start, nelmts).then(|| {
+            let a = *cursor;
+            let size = dblk_size(nelmts) as u64;
+            *cursor += size;
+            ndata_blks += 1;
+            data_blk_size += size;
+            realized += nelmts as u64;
+            a
+        });
+        DataBlock {
+            start,
+            nelmts,
+            addr,
         }
-    }
-    let n_direct_dblks = dblk_sizes.len();
-
-    // Super block addresses (for super blocks sblk_min..nsblks-1)
-    let n_sblk_addrs = nsblks.saturating_sub(sblk_min);
-
-    // EAIB size
-    let aeib_size = 4
-        + 1
-        + 1
-        + os
-        + idx_blk_elmts as usize * elem_size
-        + n_direct_dblks * os
-        + n_sblk_addrs * os
-        + 4;
-
-    // Build AEHD
-    let mut aehd = Vec::with_capacity(aehd_size);
-    aehd.extend_from_slice(b"EAHD");
-    aehd.push(0); // version
-    aehd.push(client_id);
-    aehd.push(elem_size as u8);
-    aehd.push(max_nelmts_bits);
-    aehd.push(idx_blk_elmts);
-    aehd.push(min_dblk_nelmts);
-    aehd.push(super_blk_min_nelmts);
-    aehd.push(max_dblk_nelmts_bits);
-
-    // Count data blocks that will have chunks
-    let n_active_dblks: u64 = if remaining_after_inline > 0 {
-        let mut count = 0u64;
-        let mut ci = n_inline;
-        for &sz in &dblk_sizes {
-            if ci < num_elements {
-                count += 1;
-                ci += sz;
-            }
-        }
-        count
-    } else {
-        0
-    };
-    let blk_off_size = (max_nelmts_bits as usize).div_ceil(8);
-    let aedb_header_overhead = 4 + 1 + 1 + os + blk_off_size + 4;
-    let data_blk_total_size: u64 = if remaining_after_inline > 0 {
-        let mut total = 0u64;
-        let mut ci = n_inline;
-        for &sz in &dblk_sizes {
-            if ci < num_elements {
-                total += (aedb_header_overhead + sz * elem_size) as u64;
-                ci += sz;
-            }
-        }
-        total
-    } else {
-        0
-    };
-    let max_idx_set: u64 = if remaining_after_inline > 0 {
-        let mut max_set = idx_blk_elmts as u64;
-        let mut ci = n_inline;
-        for &sz in &dblk_sizes {
-            if ci < num_elements {
-                max_set += sz as u64;
-                ci += sz;
-            }
-        }
-        max_set
-    } else {
-        idx_blk_elmts as u64
     };
 
+    let mut direct: Vec<DataBlock> = Vec::with_capacity(ndblk_addrs);
+    for &(ndblks, nelmts, first) in &levels[..direct_levels] {
+        for k in 0..ndblks {
+            direct.push(plan_dblk(&mut cursor, first + k * nelmts, nelmts));
+        }
+    }
+    // (super block address, level, its data blocks)
+    let mut supers: Vec<(Option<u64>, usize, Vec<DataBlock>)> = Vec::with_capacity(nsblk_addrs);
+    for (u, &(ndblks, nelmts, first)) in levels.iter().enumerate().skip(direct_levels) {
+        if !defined_in(first, ndblks.saturating_mul(nelmts)) {
+            supers.push((None, u, Vec::new()));
+            continue;
+        }
+        let sb_size =
+            4 + 1 + 1 + os + arr_off_size + sblk_bitmap_len(ndblks, nelmts) + ndblks * os + 4;
+        let sb_addr = cursor;
+        cursor += sb_size as u64;
+        nsuper_blks += 1;
+        super_blk_size += sb_size as u64;
+        let dblks = (0..ndblks)
+            .map(|k| plan_dblk(&mut cursor, first + k * nelmts, nelmts))
+            .collect();
+        supers.push((Some(sb_addr), u, dblks));
+    }
+
+    let slot = |i: usize| slots.get(i).and_then(Option::as_ref);
     let write_length = |buf: &mut Vec<u8>, val: u64| match length_size {
         4 => buf.extend_from_slice(&(val as u32).to_le_bytes()),
         _ => buf.extend_from_slice(&val.to_le_bytes()),
     };
-    let write_addr = |buf: &mut Vec<u8>, val: u64| match offset_size {
-        4 => buf.extend_from_slice(&(val as u32).to_le_bytes()),
-        _ => buf.extend_from_slice(&val.to_le_bytes()),
+    let write_addr_opt = |buf: &mut Vec<u8>, addr: Option<u64>| match addr {
+        Some(a) => push_addr(buf, a, offset_size),
+        None => buf.extend(core::iter::repeat_n(0xFF, os)),
+    };
+    let block_prefix = |buf: &mut Vec<u8>, sig: &[u8; 4], block_off: usize| {
+        buf.extend_from_slice(sig);
+        buf.push(0); // version
+        buf.push(client_id);
+        push_addr(buf, ea_base_address, offset_size);
+        buf.extend_from_slice(&(block_off as u64).to_le_bytes()[..arr_off_size]);
+    };
+    // Serialise one data block (paged or not) onto `out`.
+    let write_dblk = |out: &mut Vec<u8>, db: &DataBlock| {
+        let at = out.len();
+        block_prefix(out, b"EADB", db.start);
+        let first = idx_blk + db.start;
+        if db.nelmts > page_nelmts {
+            // Paged: the prefix carries only its own checksum; each page
+            // follows with one of its own.
+            let sum = jenkins_lookup3(&out[at..]);
+            out.extend_from_slice(&sum.to_le_bytes());
+            for p in 0..db.nelmts / page_nelmts {
+                let page_at = out.len();
+                for e in 0..page_nelmts {
+                    let i = first + p * page_nelmts + e;
+                    push_index_element(out, slot(i), offset_size, chunk_size_bytes);
+                }
+                let sum = jenkins_lookup3(&out[page_at..]);
+                out.extend_from_slice(&sum.to_le_bytes());
+            }
+        } else {
+            for i in first..first + db.nelmts {
+                push_index_element(out, slot(i), offset_size, chunk_size_bytes);
+            }
+            let sum = jenkins_lookup3(&out[at..]);
+            out.extend_from_slice(&sum.to_le_bytes());
+        }
+        debug_assert_eq!(out.len() - at, dblk_size(db.nelmts));
     };
 
-    write_length(&mut aehd, 0);
-    write_length(&mut aehd, 0);
-    write_length(&mut aehd, n_active_dblks);
-    write_length(&mut aehd, data_blk_total_size);
-    write_length(&mut aehd, num_elements as u64);
-    write_length(&mut aehd, max_idx_set);
+    // Header (EAHD). The six statistics are, in order: super blocks, their
+    // bytes, data blocks, their bytes, max index set, elements realised.
+    let mut out = Vec::with_capacity((cursor - ea_base_address) as usize);
+    out.extend_from_slice(b"EAHD");
+    out.push(0); // version
+    out.push(client_id);
+    out.push(elem_size as u8);
+    out.push(MAX_NELMTS_BITS);
+    out.push(IDX_BLK_ELMTS);
+    out.push(DATA_BLK_MIN_ELMTS);
+    out.push(SUP_BLK_MIN_DATA_PTRS);
+    out.push(MAX_DBLK_PAGE_NELMTS_BITS);
+    write_length(&mut out, nsuper_blks);
+    write_length(&mut out, super_blk_size);
+    write_length(&mut out, ndata_blks);
+    write_length(&mut out, data_blk_size);
+    write_length(&mut out, max_idx_set as u64);
+    write_length(&mut out, realized);
+    push_addr(&mut out, aeib_address, offset_size);
+    let sum = jenkins_lookup3(&out);
+    out.extend_from_slice(&sum.to_le_bytes());
+    debug_assert_eq!(out.len(), aehd_size);
 
-    write_addr(&mut aehd, aeib_address);
-
-    let aehd_checksum = jenkins_lookup3(&aehd);
-    aehd.extend_from_slice(&aehd_checksum.to_le_bytes());
-    debug_assert_eq!(aehd.len(), aehd_size);
-
-    // Build AEIB
-    let mut aeib = Vec::with_capacity(aeib_size);
-    aeib.extend_from_slice(b"EAIB");
-    aeib.push(0);
-    aeib.push(client_id);
-
-    match offset_size {
-        4 => aeib.extend_from_slice(&(ea_base_address as u32).to_le_bytes()),
-        8 => aeib.extend_from_slice(&ea_base_address.to_le_bytes()),
-        _ => aeib.extend_from_slice(&ea_base_address.to_le_bytes()),
+    // Index block (EAIB): inline elements, data block and super block
+    // addresses.
+    let ib_start = out.len();
+    out.extend_from_slice(b"EAIB");
+    out.push(0);
+    out.push(client_id);
+    push_addr(&mut out, ea_base_address, offset_size);
+    for i in 0..idx_blk {
+        push_index_element(&mut out, slot(i), offset_size, chunk_size_bytes);
     }
-
-    // Inline elements
-    #[allow(clippy::needless_range_loop)]
-    for i in 0..idx_blk_elmts as usize {
-        if i < n_inline {
-            write_chunk_element(
-                &mut aeib,
-                &chunks[i],
-                offset_size,
-                has_filters,
-                chunk_size_bytes,
-            );
-        } else {
-            write_undefined_element(&mut aeib, offset_size, has_filters, chunk_size_bytes);
+    for db in &direct {
+        write_addr_opt(&mut out, db.addr);
     }
+    for (sb_addr, _, _) in &supers {
+        write_addr_opt(&mut out, *sb_addr);
     }
+    let sum = jenkins_lookup3(&out[ib_start..]);
+    out.extend_from_slice(&sum.to_le_bytes());
+    debug_assert_eq!(out.len() - ib_start, aeib_size);
 
-    // Data block addresses + build data blocks
-    let mut data_blocks_buf = Vec::new();
-    let dblks_base = aeib_address + aeib_size as u64;
-    let mut dblk_cursor = dblks_base;
-    let mut chunk_idx = n_inline;
-
-    for &nelmts in &dblk_sizes {
-        if chunk_idx >= num_elements {
-            match offset_size {
-                4 => aeib.extend_from_slice(&u32::MAX.to_le_bytes()),
-                8 => aeib.extend_from_slice(&u64::MAX.to_le_bytes()),
-                _ => aeib.extend_from_slice(&u64::MAX.to_le_bytes()),
+    for db in direct.iter().filter(|d| d.addr.is_some()) {
+        write_dblk(&mut out, db);
     }
+    for (sb_addr, u, dblks) in &supers {
+        if sb_addr.is_none() {
             continue;
         }
-
-        match offset_size {
-            4 => aeib.extend_from_slice(&(dblk_cursor as u32).to_le_bytes()),
-            8 => aeib.extend_from_slice(&dblk_cursor.to_le_bytes()),
-            _ => aeib.extend_from_slice(&dblk_cursor.to_le_bytes()),
-        }
-
-        // Build EADB
-        let mut aedb = Vec::new();
-        aedb.extend_from_slice(b"EADB");
-        aedb.push(0);
-        aedb.push(client_id);
-        match offset_size {
-            4 => aedb.extend_from_slice(&(ea_base_address as u32).to_le_bytes()),
-            8 => aedb.extend_from_slice(&ea_base_address.to_le_bytes()),
-            _ => aedb.extend_from_slice(&ea_base_address.to_le_bytes()),
-        }
-
-        let blk_off_size = (max_nelmts_bits as usize).div_ceil(8);
-        let blk_off_val = (chunk_idx - n_inline) as u64;
-        aedb.extend_from_slice(&blk_off_val.to_le_bytes()[..blk_off_size]);
-
-        for slot in 0..nelmts {
-            if chunk_idx + slot < num_elements {
-                write_chunk_element(
-                    &mut aedb,
-                    &chunks[chunk_idx + slot],
-                    offset_size,
-                    has_filters,
-                    chunk_size_bytes,
-                );
-            } else {
-                write_undefined_element(&mut aedb, offset_size, has_filters, chunk_size_bytes);
+        let (ndblks, nelmts, first) = levels[*u];
+        let sb_start = out.len();
+        block_prefix(&mut out, b"EASB", first);
+        if nelmts > page_nelmts {
+            // Page-init bits, `npages` per data block, packed MSB-first
+            // (`H5VM_bit_set`): every page of an allocated data block is
+            // written.
+            let npages = nelmts / page_nelmts;
+            let mut bitmap = vec![0u8; sblk_bitmap_len(ndblks, nelmts)];
+            for (k, db) in dblks.iter().enumerate() {
+                if db.addr.is_some() {
+                    for p in 0..npages {
+                        let bit = k * npages + p;
+                        bitmap[bit / 8] |= 0x80 >> (bit % 8);
                     }
                 }
-
-        let aedb_checksum = jenkins_lookup3(&aedb);
-        aedb.extend_from_slice(&aedb_checksum.to_le_bytes());
-
-        dblk_cursor += aedb.len() as u64;
-        data_blocks_buf.extend_from_slice(&aedb);
-        chunk_idx += nelmts;
             }
-
-    // Super block addresses (all undefined)
-    for _ in 0..n_sblk_addrs {
-        match offset_size {
-            4 => aeib.extend_from_slice(&u32::MAX.to_le_bytes()),
-            8 => aeib.extend_from_slice(&u64::MAX.to_le_bytes()),
-            _ => aeib.extend_from_slice(&u64::MAX.to_le_bytes()),
+            out.extend_from_slice(&bitmap);
+        }
+        for db in dblks {
+            write_addr_opt(&mut out, db.addr);
+        }
+        let sum = jenkins_lookup3(&out[sb_start..]);
+        out.extend_from_slice(&sum.to_le_bytes());
+        for db in dblks.iter().filter(|d| d.addr.is_some()) {
+            write_dblk(&mut out, db);
         }
     }
-
-    let aeib_checksum = jenkins_lookup3(&aeib);
-    aeib.extend_from_slice(&aeib_checksum.to_le_bytes());
-    debug_assert_eq!(aeib.len(), aeib_size);
-
-    let mut combined = aehd;
-    combined.extend_from_slice(&aeib);
-    combined.extend_from_slice(&data_blocks_buf);
-    combined
-}
-
-fn write_chunk_element(
-    buf: &mut Vec<u8>,
-    chunk: &WrittenChunk,
-    offset_size: u8,
-    has_filters: bool,
-    chunk_size_bytes: usize,
-) {
-    match offset_size {
-        4 => buf.extend_from_slice(&(chunk.address as u32).to_le_bytes()),
-        8 => buf.extend_from_slice(&chunk.address.to_le_bytes()),
-        _ => buf.extend_from_slice(&chunk.address.to_le_bytes()),
-    }
-    if has_filters {
-        let cs_bytes = chunk.compressed_size.to_le_bytes();
-        buf.extend_from_slice(&cs_bytes[..chunk_size_bytes]);
-        buf.extend_from_slice(&chunk.filter_mask.to_le_bytes());
-    }
-}
-
-fn write_undefined_element(
-    buf: &mut Vec<u8>,
-    offset_size: u8,
-    has_filters: bool,
-    chunk_size_bytes: usize,
-) {
-    let os = offset_size as usize;
-    // Use extend with repeat to avoid heap-allocating a temporary Vec on each call.
-    buf.extend(core::iter::repeat_n(0xFF, os));
-    if has_filters {
-        buf.extend(core::iter::repeat_n(0x00, chunk_size_bytes));
-        buf.extend_from_slice(&0u32.to_le_bytes());
-    }
+    debug_assert_eq!(out.len() as u64, cursor - ea_base_address);
+    out
 }

crates/clawhdf5-format/src/error.rs

@@ -80,6 +80,9 @@ pub enum FormatError {
     InvalidLocalHeapSignature,
     /// Invalid local heap version.
     InvalidLocalHeapVersion(u8),
+    /// A local heap's free list points outside its data segment (libhdf5:
+    /// "bad heap free list").
+    InvalidLocalHeapFreeList,
     /// Invalid B-tree v1 signature.
     InvalidBTreeSignature,
     /// Invalid B-tree node type.
@@ -117,6 +120,14 @@ pub enum FormatError {
     /// A message is marked shared but was parsed without access to the file,
     /// so the reference to the real message could not be followed.
     UnresolvedSharedMessage,
+    /// A shared-message reference points at an object header that holds no
+    /// (unshared) message of the referenced type (raw message type id).
+    SharedMessageTargetMissing(u16),
+    /// A superblock was parsed at a non-zero offset of the buffer (the file
+    /// has a user block of this many bytes). HDF5 addresses are relative to
+    /// the superblock, so the buffer must start there: see
+    /// `signature::split_user_block`.
+    UserBlockNotStripped(u64),
     /// A selection does not fit the dataset it was applied to (wrong rank, or
     /// it reaches past a dimension's extent).
     SelectionOutOfBounds(String),
@@ -190,6 +201,28 @@ pub enum FormatError {
     DuplicateDatasetName(String),
     /// Integer overflow in size computation (malformed data protection).
     Overflow(String),
+    /// An object header that libhdf5 refuses to load (the reason is
+    /// libhdf5's own error text): a misaligned or overrunning message, a
+    /// wrong message count, contradictory message flags, a message of a
+    /// class that cannot be shared flagged shareable, …
+    InvalidObjectHeader(&'static str),
+    /// A datatype message libhdf5 refuses to decode (the reason is
+    /// libhdf5's own error text): size 0, bit fields outside the type,
+    /// an empty enum name, a compound member outside its compound, …
+    InvalidDatatype(String),
+    /// A chunked layout whose chunk dimensions libhdf5 refuses: a zero
+    /// dimension, a rank that does not match the dataspace, an element size
+    /// that is not the datatype's, or a chunk of 4 GiB or more indexed by a
+    /// version-1 B-tree.
+    InvalidChunkDimensions(String),
+    /// The superblock's end-of-file address lies past the end of the file:
+    /// the file was truncated (libhdf5 refuses to open it).
+    TruncatedFile {
+        /// End of file recorded in the superblock (relative to byte 0).
+        stored_eof: u64,
+        /// The file's actual length in bytes.
+        actual_len: u64,
+    },
 }
 
 impl fmt::Display for FormatError {
@@ -270,6 +303,9 @@ impl fmt::Display for FormatError {
             FormatError::InvalidLocalHeapSignature => {
                 write!(f, "invalid local heap signature")
             }
+            FormatError::InvalidLocalHeapFreeList => {
+                write!(f, "bad local heap free list")
+            }
             FormatError::InvalidLocalHeapVersion(v) => {
                 write!(f, "invalid local heap version: {v}")
             }
@@ -339,6 +375,16 @@ impl fmt::Display for FormatError {
             FormatError::SelectionOutOfBounds(msg) => {
                 write!(f, "selection out of bounds: {msg}")
             }
+            FormatError::UserBlockNotStripped(n) => write!(
+                f,
+                "file has a {n}-byte user block: parse the bytes from the superblock on \
+                 (signature::split_user_block)"
+            ),
+            FormatError::SharedMessageTargetMissing(t) => write!(
+                f,
+                "shared message reference points at an object header with no message of type \
+                 {t:#06x}"
+            ),
             FormatError::UnresolvedSharedMessage => write!(
                 f,
                 "message is shared but no file data was available to resolve it"
@@ -382,9 +428,17 @@ impl fmt::Display for FormatError {
             FormatError::InvalidFilterPipelineVersion(v) => {
                 write!(f, "invalid filter pipeline version: {v}")
             }
-            FormatError::UnsupportedFilter(id) => {
-                write!(f, "unsupported filter: {id}")
-            }
+            FormatError::UnsupportedFilter(id) => match crate::filter_registry::known_filter(*id) {
+                Some((name, Some(feature))) => write!(
+                    f,
+                    "unsupported filter: {id} ({name}; this build lacks the `{feature}` feature)"
+                ),
+                Some((name, None)) => write!(
+                    f,
+                    "unsupported filter: {id} ({name}, not implemented by clawhdf5)"
+                ),
+                None => write!(f, "unsupported filter: {id}"),
+            },
             FormatError::FilterError(msg) => {
                 write!(f, "filter error: {msg}")
             }
@@ -421,6 +475,25 @@ impl fmt::Display for FormatError {
             FormatError::Overflow(msg) => {
                 write!(f, "integer overflow: {msg}")
             }
+            FormatError::InvalidObjectHeader(why) => {
+                write!(f, "corrupt object header: {why}")
+            }
+            FormatError::InvalidDatatype(why) => {
+                write!(f, "invalid datatype: {why}")
+            }
+            FormatError::InvalidChunkDimensions(why) => {
+                write!(f, "invalid chunk dimensions: {why}")
+            }
+            FormatError::TruncatedFile {
+                stored_eof,
+                actual_len,
+            } => {
+                write!(
+                    f,
+                    "truncated file: the superblock records end of file {stored_eof}, \
+                     but the file is {actual_len} bytes"
+                )
+            }
         }
     }
 }

crates/clawhdf5-format/src/extensible_array.rs

@@ -9,9 +9,35 @@ extern crate alloc;
 #[cfg(not(feature = "std"))]
 use alloc::{format, vec, vec::Vec};
 
+use crate::chunk_grid::ChunkGrid;
 use crate::chunked_read::ChunkInfo;
 use crate::error::FormatError;
 
+/// Verify the Jenkins lookup3 checksum stored immediately after
+/// `data[start..end]`, as every Extensible Array structure carries one.
+///
+/// A corrupt chunk index yields addresses pointing at the wrong bytes, so a
+/// mismatch is an error: otherwise the damage surfaces as plausible data read
+/// from the wrong chunk.
+#[cfg(feature = "checksum")]
+fn verify_checksum(data: &[u8], start: usize, end: usize) -> Result<(), FormatError> {
+    ensure_len(data, end, 4)?;
+    let stored = u32::from_le_bytes([data[end], data[end + 1], data[end + 2], data[end + 3]]);
+    let computed = crate::checksum::jenkins_lookup3(&data[start..end]);
+    if computed != stored {
+        return Err(FormatError::ChecksumMismatch {
+            expected: stored,
+            computed,
+        });
+    }
+    Ok(())
+}
+
+#[cfg(not(feature = "checksum"))]
+fn verify_checksum(_data: &[u8], _start: usize, _end: usize) -> Result<(), FormatError> {
+    Ok(())
+}
+
 /// Parsed Extensible Array header (AEHD).
 #[derive(Debug, Clone)]
 pub struct ExtensibleArrayHeader {
@@ -145,6 +171,8 @@ impl ExtensibleArrayHeader {
         pos += ls; // skip nelmts
         pos += ls; // skip max_idx_set (6th stats field)
         let index_block_address = read_offset(d, pos, offset_size)?;
+        pos += offset_size as usize;
+        verify_checksum(file_data, offset, offset + pos)?;
 
         Ok(ExtensibleArrayHeader {
             client_id,
@@ -176,8 +204,7 @@ fn read_element(
     offset_size: u8,
     chunk_byte_size: u64,
     linear_index: usize,
-    num_chunks_per_dim: &[u64],
-    chunk_dimensions: &[u32],
+    grid: &ChunkGrid,
 ) -> Result<(Option<ChunkInfo>, usize), FormatError> {
     let os = offset_size as usize;
 
@@ -193,7 +220,10 @@ fn read_element(
             return Ok((None, os));
         }
         let address = read_offset(data, pos, offset_size)?;
-        let offsets = index_to_chunk_offsets(linear_index, num_chunks_per_dim, chunk_dimensions);
+        // A slot beyond the current extent is ignored, as the library does.
+        let Some(offsets) = grid.offsets(linear_index as u64) else {
+            return Ok((None, os));
+        };
         Ok((
             Some(ChunkInfo {
                 chunk_size: chunk_byte_size as u32,
@@ -234,7 +264,9 @@ fn read_element(
             data[fm_off + 2],
             data[fm_off + 3],
         ]);
-        let offsets = index_to_chunk_offsets(linear_index, num_chunks_per_dim, chunk_dimensions);
+        let Some(offsets) = grid.offsets(linear_index as u64) else {
+            return Ok((None, elem_total));
+        };
         Ok((
             Some(ChunkInfo {
                 chunk_size: chunk_size as u32,
@@ -247,28 +279,41 @@ fn read_element(
     }
 }
 
-/// Convert a linear chunk index to N-dimensional chunk offsets in dataset space.
-fn index_to_chunk_offsets(
-    index: usize,
-    num_chunks_per_dim: &[u64],
-    chunk_dimensions: &[u32],
-) -> Vec<u64> {
-    let rank = num_chunks_per_dim.len();
-    let mut offsets = vec![0u64; rank];
-    let mut remaining = index as u64;
-    for d in (0..rank).rev() {
-        let nchunks = num_chunks_per_dim[d];
-        if nchunks == 0 {
-            continue;
-        }
-        let chunk_idx = remaining % nchunks;
-        remaining /= nchunks;
-        offsets[d] = chunk_idx * chunk_dimensions[d] as u64;
-    }
-    offsets
+/// Collect elements from a data block at the given offset.
+#[allow(clippy::too_many_arguments)]
+/// Layout of super block `u`, per the HDF5 spec: the number of data blocks it
+/// owns and how many elements each of them holds.
+///
+/// `ndblks` and `dblk_nelmts` each double every *other* level, a half-step
+/// apart, so the blocks grow as 1x16, 1x32, 2x32, 2x64, 4x64 ... for a
+/// 16-element minimum. Treating either as doubling every level (the previous
+/// implementation) puts every element after the first data block at the wrong
+/// index.
+fn sblk_info(u: usize, data_blk_min_elmts: usize) -> Option<(usize, usize)> {
+    let ndblks = 1usize.checked_shl((u / 2) as u32)?;
+    let dblk_nelmts = 1usize
+        .checked_shl(u.div_ceil(2) as u32)?
+        .checked_mul(data_blk_min_elmts)?;
+    Some((ndblks, dblk_nelmts))
 }
 
-/// Collect elements from a data block at the given offset.
+/// Width of the "offset of the block in the array" field carried by super and
+/// data blocks (`hdr->arr_off_size`).
+fn arr_off_size(header: &ExtensibleArrayHeader) -> usize {
+    (header.max_nelmts_bits as usize).div_ceil(8)
+}
+
+/// Elements per data block page, once a data block is large enough to be paged.
+fn page_nelmts(header: &ExtensibleArrayHeader) -> Option<usize> {
+    1usize.checked_shl(u32::from(header.max_dblk_nelmts_bits))
+}
+
+/// Read the elements of one data block (EADB).
+///
+/// `page_init` is the owning super block's page-init bitmap and `first_page`
+/// this block's first bit in it; both are only consulted when the block is
+/// paged. The bitmap lives in the super block, not here — a paged data block
+/// stores only its prefix, then one slot per page.
 #[allow(clippy::too_many_arguments)]
 fn read_data_block_elements(
     file_data: &[u8],
@@ -278,119 +323,101 @@ fn read_data_block_elements(
     offset_size: u8,
     chunk_byte_size: u64,
     start_index: usize,
-    num_chunks_per_dim: &[u64],
-    chunk_dimensions: &[u32],
+    grid: &ChunkGrid,
+    page_init: &[u8],
+    first_page: usize,
 ) -> Result<Vec<ChunkInfo>, FormatError> {
-    // AEDB: signature(4) + version(1) + client_id(1) + header_address(offset_size)
-    let db_header_size = 4 + 1 + 1 + offset_size as usize;
+    // EADB: signature(4) + version(1) + client_id(1) + header_address(offset_size)
+    //       + block offset(arr_off_size)
+    let db_header_size = 4 + 1 + 1 + offset_size as usize + arr_off_size(header);
     ensure_len(file_data, db_offset, db_header_size)?;
 
-    let d = &file_data[db_offset..];
-    if &d[0..4] != b"EADB" {
+    if &file_data[db_offset..db_offset + 4] != b"EADB" {
         return Err(FormatError::ChunkedReadError(
             "invalid Extensible Array data block signature".into(),
         ));
     }
-    // Skip version(1) + client_id(1) + header_address(offset_size) + block_offset
-    // Block offset is encoded in ceil(max_nelmts_bits/8) bytes
-    let blk_off_size = (header.max_nelmts_bits as usize).div_ceil(8);
-    let mut pos = db_offset + db_header_size + blk_off_size;
 
-    // Check if paged
-    if header.max_nelmts_bits >= usize::BITS as u8 {
-        return Err(FormatError::Overflow(
-            "max_nelmts_bits exceeds usize bit width".into(),
-        ));
-    }
-    let page_nelmts = 1usize << header.max_nelmts_bits;
-    let is_paged = nelmts > page_nelmts;
+    let mut pos = db_offset + db_header_size;
+    let page = page_nelmts(header).ok_or_else(|| {
+        FormatError::Overflow("Extensible Array page element count overflows usize".into())
+    })?;
 
     let mut chunks = Vec::new();
-
-    if !is_paged {
-        for i in 0..nelmts {
+    let read_run = |from: usize,
+                    count: usize,
+                    first_index: usize,
+                    chunks: &mut Vec<ChunkInfo>|
+     -> Result<usize, FormatError> {
+        let mut p = from;
+        for i in 0..count {
             let (info, consumed) = read_element(
                 file_data,
-                pos,
+                p,
                 header.client_id,
                 header.element_size,
                 offset_size,
                 chunk_byte_size,
-                start_index + i,
-                num_chunks_per_dim,
-                chunk_dimensions,
+                first_index + i,
+                grid,
             )?;
             if let Some(ci) = info {
                 chunks.push(ci);
             }
-            pos += consumed;
+            p += consumed;
         }
-    } else {
-        // Paged: elements are split into pages of page_nelmts.
-        // After the data block header comes a page bitmap, then each page
-        // has page_nelmts elements followed by a 4-byte checksum.
-        let npages = nelmts.div_ceil(page_nelmts);
-        // Page bitmap: ceil(npages / 8) bytes
-        let bitmap_size = npages.div_ceil(8);
-        // Read bitmap
-        if pos + bitmap_size > file_data.len() {
-            return Err(FormatError::UnexpectedEof {
-                expected: pos + bitmap_size,
-                available: file_data.len(),
-            });
-        }
-        let bitmap = &file_data[pos..pos + bitmap_size];
-        pos += bitmap_size;
+        Ok(p)
+    };
 
+    if nelmts <= page {
+        // Prefix and elements are covered by one checksum.
         let elem_bytes = if header.client_id == 0 {
             offset_size as usize
         } else {
             header.element_size as usize
         };
-
-        let mut global_idx = start_index;
-        for page_idx in 0..npages {
-            let byte_idx = page_idx / 8;
-            let bit_idx = page_idx % 8;
-            let page_has_data = (bitmap[byte_idx] >> bit_idx) & 1 != 0;
-
-            let elems_this_page = if page_idx == npages - 1 {
-                let remainder = nelmts % page_nelmts;
-                if remainder == 0 {
-                    page_nelmts
-                } else {
-                    remainder
+        let end = nelmts
+            .checked_mul(elem_bytes)
+            .and_then(|b| pos.checked_add(b))
+            .ok_or_else(|| FormatError::Overflow("Extensible Array data block span".into()))?;
+        verify_checksum(file_data, db_offset, end)?;
+        read_run(pos, nelmts, start_index, &mut chunks)?;
+        return Ok(chunks);
     }
-            } else {
-                page_nelmts
-            };
 
-            if page_has_data {
-                for i in 0..elems_this_page {
-                    let (info, consumed) = read_element(
-                        file_data,
-                        pos,
-                        header.client_id,
-                        header.element_size,
-                        offset_size,
-                        chunk_byte_size,
-                        global_idx + i,
-                        num_chunks_per_dim,
-                        chunk_dimensions,
-                    )?;
-                    if let Some(ci) = info {
-                        chunks.push(ci);
-                    }
-                    pos += consumed;
-                }
-                // Skip page checksum (4 bytes)
+    // Paged: the prefix ends with its own checksum, then one slot per page,
+    // each holding `page` elements followed by a checksum. Pages whose bit is
+    // clear were never written; their slot still occupies the file, so stride
+    // over it rather than reading zeros as addresses.
+    verify_checksum(file_data, db_offset, pos)?;
     pos += 4;
+    let elem_bytes = if header.client_id == 0 {
+        offset_size as usize
     } else {
-                // Empty page: skip all elements + checksum
-                pos += elems_this_page * elem_bytes + 4;
-            }
-            global_idx += elems_this_page;
+        header.element_size as usize
+    };
+    let page_stride = page
+        .checked_mul(elem_bytes)
+        .and_then(|b| b.checked_add(4))
+        .ok_or_else(|| FormatError::Overflow("Extensible Array page stride".into()))?;
+    let npages = nelmts.div_ceil(page);
+    for p in 0..npages {
+        // One bit per page across the whole super block, packed contiguously
+        // and MSB-first within each byte, as H5VM_bit_get reads it.
+        let bit = first_page + p;
+        let initialised = page_init
+            .get(bit / 8)
+            .is_some_and(|byte| byte & (0x80 >> (bit % 8)) != 0);
+        if initialised {
+            let count = core::cmp::min(page, nelmts - p * page);
+            // Each page carries its own checksum, over a full page's worth of
+            // slots even when the last one holds fewer live elements.
+            verify_checksum(file_data, pos, pos + page * elem_bytes)?;
+            read_run(pos, count, start_index + p * page, &mut chunks)?;
         }
+        pos = pos
+            .checked_add(page_stride)
+            .ok_or_else(|| FormatError::Overflow("Extensible Array page offset".into()))?;
     }
 
     Ok(chunks)
@@ -404,53 +431,100 @@ pub fn read_extensible_array_chunks(
     file_data: &[u8],
     header: &ExtensibleArrayHeader,
     dataset_dims: &[u64],
+    max_dims: Option<&[u64]>,
     chunk_dimensions: &[u32],
     element_size: u32,
     offset_size: u8,
     _length_size: u8,
 ) -> Result<Vec<ChunkInfo>, FormatError> {
-    let rank = chunk_dimensions.len();
     let os = offset_size as usize;
 
-    let mut num_chunks_per_dim = Vec::with_capacity(rank);
-    for d in 0..rank {
-        let ch_dim = chunk_dimensions[d] as u64;
-        if ch_dim == 0 {
-            return Err(FormatError::ChunkedReadError(
-                "chunk dimension is zero".into(),
-            ));
-        }
-        let ds_dim = dataset_dims[d];
-        num_chunks_per_dim.push(ds_dim.div_ceil(ch_dim));
-    }
+    // Linear indexes follow the maximum dimensions, with the unlimited
+    // dimension swizzled to the slowest position (see `chunk_grid`).
+    let dims_u64: Vec<u64> = chunk_dimensions.iter().map(|&d| d as u64).collect();
+    let grid = ChunkGrid::extensible_array(dataset_dims, max_dims, &dims_u64)?;
+    let grid = &grid;
 
     let chunk_byte_size: u64 =
         chunk_dimensions.iter().map(|&d| d as u64).product::<u64>() * element_size as u64;
 
-    // Parse index block (AEIB)
+    // Parse index block (EAIB): signature(4) + version(1) + client_id(1)
+    // + header address(offset_size), then the inline elements, then the
+    // direct data block addresses, then the super block addresses.
     let ib_offset = header.index_block_address as usize;
-    let ib_header_size = 4 + 1 + 1 + offset_size as usize; // sig + ver + client + hdr_addr
+    let ib_header_size = 4 + 1 + 1 + os;
     ensure_len(file_data, ib_offset, ib_header_size)?;
 
-    let ib = &file_data[ib_offset..];
-    if &ib[0..4] != b"EAIB" {
+    if &file_data[ib_offset..ib_offset + 4] != b"EAIB" {
         return Err(FormatError::ChunkedReadError(
             "invalid Extensible Array index block signature".into(),
         ));
     }
-    // Skip version(1) + client_id(1) + header_address(offset_size)
     let mut pos = ib_offset + ib_header_size;
 
     let mut chunks = Vec::new();
-    let mut global_index = 0usize;
     let total_elements = header.num_elements as usize;
 
-    // 1. Read inline elements in index block
-    let n_inline = header.idx_blk_elmts as usize;
-    for i in 0..n_inline {
-        if global_index + i >= total_elements {
-            break;
+    let dmin = header.min_dblk_nelmts as usize;
+    if dmin == 0 || !dmin.is_power_of_two() {
+        return Err(FormatError::ChunkedReadError(
+            "Extensible Array data block minimum is not a power of two".into(),
+        ));
     }
+    // nsblks = 1 + (max_nelmts_bits - log2(data_blk_min_elmts)), and the index
+    // block holds 2 * (sup_blk_min_data_ptrs - 1) data block addresses.
+    let log2_dmin = dmin.trailing_zeros() as usize;
+    let nsblks = 1 + (header.max_nelmts_bits as usize).saturating_sub(log2_dmin);
+    let ndblk_addrs = 2 * (header.super_blk_min_nelmts as usize).saturating_sub(1);
+
+    // The data blocks listed directly in the index block are the first
+    // `ndblk_addrs` in super-block order, each sized by the level it belongs
+    // to; the super block addresses that follow resume at the next level.
+    let mut direct: Vec<usize> = Vec::with_capacity(ndblk_addrs);
+    let mut level = 0usize;
+    while direct.len() < ndblk_addrs {
+        if level >= nsblks {
+            return Err(FormatError::ChunkedReadError(
+                "Extensible Array index block claims more data blocks than the array has".into(),
+            ));
+        }
+        let (ndblks, dblk_nelmts) = sblk_info(level, dmin).ok_or_else(|| {
+            FormatError::Overflow("Extensible Array super block layout overflows usize".into())
+        })?;
+        for _ in 0..ndblks {
+            direct.push(dblk_nelmts);
+        }
+        level += 1;
+    }
+    if direct.len() != ndblk_addrs {
+        // A partial level in the index block is not a layout HDF5 produces,
+        // and guessing where the super blocks resume would misplace elements.
+        return Err(FormatError::ChunkedReadError(
+            "Extensible Array index block ends mid super block".into(),
+        ));
+    }
+
+    // One checksum covers the prefix, every inline element slot, and every
+    // data block and super block address.
+    let elem_bytes = if header.client_id == 0 {
+        os
+    } else {
+        header.element_size as usize
+    };
+    let ib_end = (header.idx_blk_elmts as usize)
+        .checked_mul(elem_bytes)
+        .and_then(|b| pos.checked_add(b))
+        .and_then(|p| {
+            ndblk_addrs
+                .checked_add(nsblks - level)
+                .and_then(|n| n.checked_mul(os).and_then(|b| p.checked_add(b)))
+        })
+        .ok_or_else(|| FormatError::Overflow("Extensible Array index block span".into()))?;
+    verify_checksum(file_data, ib_offset, ib_end)?;
+
+    // 1. Elements stored inline in the index block.
+    let n_inline = (header.idx_blk_elmts as usize).min(total_elements);
+    for i in 0..n_inline {
         let (info, consumed) = read_element(
             file_data,
             pos,
@@ -458,174 +532,104 @@ pub fn read_extensible_array_chunks(
             header.element_size,
             offset_size,
             chunk_byte_size,
-            global_index + i,
-            &num_chunks_per_dim,
-            chunk_dimensions,
+            i,
+            grid,
         )?;
         if let Some(ci) = info {
             chunks.push(ci);
         }
         pos += consumed;
     }
-    global_index += n_inline.min(total_elements);
-
-    // If all elements were inline, we're done
+    let mut global_index = n_inline;
     if global_index >= total_elements {
         return Ok(chunks);
     }
 
-    // Compute data block and super block counts
-    let min_dblk = header.min_dblk_nelmts as usize;
-    let sblk_min = header.super_blk_min_nelmts as usize;
-
-    // The first sblk_min super block levels have their data blocks listed directly
-    // in the index block. Compute their sizes.
-    let mut n_direct_dblks = 0usize;
-    let mut dblk_sizes: Vec<usize> = Vec::new();
-    {
-        let mut nelmts = min_dblk;
-        for sb_level in 0..sblk_min {
-            if sb_level >= usize::BITS as usize {
-                return Err(FormatError::Overflow(
-                    "sb_level exceeds usize bit width".into(),
+    // 2. Data blocks listed directly in the index block.
+    for &dblk_nelmts in &direct {
+        if global_index >= total_elements {
+            return Ok(chunks);
+        }
+        ensure_len(file_data, pos, os)?;
+        let addr = read_offset(file_data, pos, offset_size)?;
+        pos += os;
+        if !is_undefined_addr(addr, offset_size) {
+            if dblk_nelmts > page_nelmts(header).unwrap_or(usize::MAX) {
+                // Would need a page-init bitmap, which only a super block
+                // carries. HDF5 never pages these small early blocks.
+                return Err(FormatError::ChunkedReadError(
+                    "Extensible Array index block references a paged data block".into(),
                 ));
             }
-            let ndblks = 1usize << sb_level;
-            for _ in 0..ndblks {
-                dblk_sizes.push(nelmts);
-                n_direct_dblks += 1;
-            }
-            if sb_level > 0 {
-                nelmts *= 2;
-            }
-        }
-    }
-
-    // Read direct data block addresses from index block
-    let mut dblk_addrs: Vec<u64> = Vec::with_capacity(n_direct_dblks);
-    for _ in 0..n_direct_dblks {
-        if pos + os > file_data.len() {
-            break;
-        }
-        let addr = read_offset(file_data, pos, offset_size)?;
-        dblk_addrs.push(addr);
-        pos += os;
-    }
-
-    // Read elements from direct data blocks
-    for (i, &addr) in dblk_addrs.iter().enumerate() {
-        if i >= dblk_sizes.len() {
-            break;
-        }
-        let nelmts = dblk_sizes[i];
-        if is_undefined_addr(addr, offset_size) {
-            global_index += nelmts;
-            continue;
-        }
-        let block_chunks = read_data_block_elements(
+            chunks.extend(read_data_block_elements(
                 file_data,
                 addr as usize,
-            nelmts,
+                dblk_nelmts,
                 header,
                 offset_size,
                 chunk_byte_size,
                 global_index,
-            &num_chunks_per_dim,
-            chunk_dimensions,
-        )?;
-        chunks.extend(block_chunks);
-        global_index += nelmts;
+                grid,
+                &[],
+                0,
+            )?);
+        }
+        global_index += dblk_nelmts;
     }
 
-    // Remaining elements are in super blocks
-    let total_in_ib_and_direct: usize = n_inline + dblk_sizes.iter().sum::<usize>();
-    if total_elements <= total_in_ib_and_direct {
-        return Ok(chunks);
-    }
-    let remaining_elements = total_elements - total_in_ib_and_direct;
-
-    // Compute super block layout
-    let mut sb_addrs: Vec<u64> = Vec::new();
-    let mut sb_infos: Vec<(usize, usize)> = Vec::new();
-    {
-        let mut covered = 0usize;
-        let mut sb_level = sblk_min;
-        let mut nelmts_per_dblk = min_dblk;
-        for lev in 0..sblk_min {
-            if lev > 0 {
-                nelmts_per_dblk *= 2;
-            }
-        }
-
-        while covered < remaining_elements {
-            if sb_level >= usize::BITS as usize {
-                return Err(FormatError::Overflow(
-                    "sb_level exceeds usize bit width".into(),
-                ));
-            }
-            let ndblks = 1usize << sb_level;
-            nelmts_per_dblk *= 2;
-            let total_in_sb = ndblks * nelmts_per_dblk;
-            sb_infos.push((ndblks, nelmts_per_dblk));
-            covered += total_in_sb;
-            sb_level += 1;
-        }
-    }
-
-    // Read super block addresses from index block
-    for _ in 0..sb_infos.len() {
-        if pos + os > file_data.len() {
+    // 3. Everything else lives in super blocks, one address per remaining
+    //    level, starting at the level after the direct data blocks.
+    for u in level..nsblks {
+        if global_index >= total_elements {
             break;
         }
-        let addr = read_offset(file_data, pos, offset_size)?;
-        sb_addrs.push(addr);
+        ensure_len(file_data, pos, os)?;
+        let sb_addr = read_offset(file_data, pos, offset_size)?;
         pos += os;
-    }
-
-    // Process each super block
-    for (sb_idx, &sb_addr) in sb_addrs.iter().enumerate() {
-        let (ndblks, nelmts_per_dblk) = sb_infos[sb_idx];
-        if is_undefined_addr(sb_addr, offset_size) {
-            global_index += ndblks * nelmts_per_dblk;
-            continue;
-        }
-        let sb_chunks = read_super_block(
+        let (ndblks, dblk_nelmts) = sblk_info(u, dmin).ok_or_else(|| {
+            FormatError::Overflow("Extensible Array super block layout overflows usize".into())
+        })?;
+        if !is_undefined_addr(sb_addr, offset_size) {
+            chunks.extend(read_super_block(
                 file_data,
                 sb_addr as usize,
                 ndblks,
-            nelmts_per_dblk,
+                dblk_nelmts,
                 header,
                 offset_size,
                 chunk_byte_size,
                 global_index,
-            &num_chunks_per_dim,
-            chunk_dimensions,
-        )?;
-        chunks.extend(sb_chunks);
-        global_index += ndblks * nelmts_per_dblk;
+                grid,
+            )?);
+        }
+        global_index =
+            global_index.saturating_add(ndblks.checked_mul(dblk_nelmts).ok_or_else(|| {
+                FormatError::Overflow("Extensible Array super block span".into())
+            })?);
     }
 
     Ok(chunks)
 }
 
-/// Read a super block (AESB) and its data blocks.
+/// Read a super block (EASB) and the data blocks it owns.
+///
+/// On disk: signature(4) + version(1) + client_id(1) + header address
+/// + block offset + the page-init bitmap for every data block it owns
+/// + one address per data block + checksum.
 #[allow(clippy::too_many_arguments)]
 fn read_super_block(
     file_data: &[u8],
     sb_offset: usize,
     ndblks: usize,
-    nelmts_per_dblk: usize,
+    dblk_nelmts: usize,
     header: &ExtensibleArrayHeader,
     offset_size: u8,
     chunk_byte_size: u64,
     start_index: usize,
-    num_chunks_per_dim: &[u64],
-    chunk_dimensions: &[u32],
+    grid: &ChunkGrid,
 ) -> Result<Vec<ChunkInfo>, FormatError> {
     let os = offset_size as usize;
-
-    // AESB: signature(4) + version(1) + client_id(1) + header_address(offset_size)
-    let sb_header_size = 4 + 1 + 1 + os;
+    let sb_header_size = 4 + 1 + 1 + os + arr_off_size(header);
     ensure_len(file_data, sb_offset, sb_header_size)?;
 
     if &file_data[sb_offset..sb_offset + 4] != b"EASB" {
@@ -634,43 +638,56 @@ fn read_super_block(
         ));
     }
 
-    let mut pos = sb_offset + sb_header_size;
-
-    // Read data block addresses
-    let mut dblk_addrs: Vec<u64> = Vec::with_capacity(ndblks);
-    for _ in 0..ndblks {
-        if pos + os > file_data.len() {
-            return Err(FormatError::UnexpectedEof {
-                expected: pos + os,
-                available: file_data.len(),
-            });
-        }
-        let addr = read_offset(file_data, pos, offset_size)?;
-        dblk_addrs.push(addr);
-        pos += os;
-    }
+    // Page-init bitmap: one bit per page, `npages` bits per data block, packed
+    // contiguously. HDF5 sizes the buffer `ndblks * ceil(npages / 8)`, which
+    // is bigger than the bits need when `npages` is not a multiple of eight.
+    // Zero-sized unless this level's data blocks are paged.
+    let page = page_nelmts(header).ok_or_else(|| {
+        FormatError::Overflow("Extensible Array page element count overflows usize".into())
+    })?;
+    let npages = if dblk_nelmts > page {
+        dblk_nelmts / page
+    } else {
+        0
+    };
+    let per_dblk_bitmap = npages.div_ceil(8);
+    let bitmap_bytes = per_dblk_bitmap
+        .checked_mul(ndblks)
+        .ok_or_else(|| FormatError::Overflow("Extensible Array page bitmap size".into()))?;
+    let bitmap_start = sb_offset + sb_header_size;
+    ensure_len(file_data, bitmap_start, bitmap_bytes)?;
+    let bitmap = &file_data[bitmap_start..bitmap_start + bitmap_bytes];
 
+    let mut pos = bitmap_start + bitmap_bytes;
     let mut chunks = Vec::new();
     let mut global_idx = start_index;
 
-    for &addr in &dblk_addrs {
-        if is_undefined_addr(addr, offset_size) {
-            global_idx += nelmts_per_dblk;
-            continue;
-        }
-        let block_chunks = read_data_block_elements(
+    // One checksum covers the prefix, the bitmap and every data block address.
+    let sb_end = ndblks
+        .checked_mul(os)
+        .and_then(|b| pos.checked_add(b))
+        .ok_or_else(|| FormatError::Overflow("Extensible Array super block span".into()))?;
+    verify_checksum(file_data, sb_offset, sb_end)?;
+
+    for i in 0..ndblks {
+        ensure_len(file_data, pos, os)?;
+        let addr = read_offset(file_data, pos, offset_size)?;
+        pos += os;
+        if !is_undefined_addr(addr, offset_size) {
+            chunks.extend(read_data_block_elements(
                 file_data,
                 addr as usize,
-            nelmts_per_dblk,
+                dblk_nelmts,
                 header,
                 offset_size,
                 chunk_byte_size,
                 global_idx,
-            num_chunks_per_dim,
-            chunk_dimensions,
-        )?;
-        chunks.extend(block_chunks);
-        global_idx += nelmts_per_dblk;
+                grid,
+                bitmap,
+                i * npages,
+            )?);
+        }
+        global_idx += dblk_nelmts;
     }
 
     Ok(chunks)
@@ -679,37 +696,28 @@ fn read_super_block(
 #[cfg(test)]
 mod tests {
     use super::*;
+
+    /// Stamp the Jenkins checksum a real file would carry over
+    /// `data[start..end]`, writing it at `end`. Hand-built fixtures need this
+    /// now that the reader validates it, exactly as HDF5 writes it.
+    fn stamp_checksum(data: &mut [u8], start: usize, end: usize) {
+        let sum = crate::checksum::jenkins_lookup3(&data[start..end]);
+        data[end..end + 4].copy_from_slice(&sum.to_le_bytes());
+    }
     #[test]
     fn index_to_offsets_1d() {
-        let num_chunks = vec![5u64];
-        let chunk_dims = vec![20u32];
-        assert_eq!(index_to_chunk_offsets(0, &num_chunks, &chunk_dims), vec![0]);
-        assert_eq!(
-            index_to_chunk_offsets(1, &num_chunks, &chunk_dims),
-            vec![20]
-        );
-        assert_eq!(
-            index_to_chunk_offsets(4, &num_chunks, &chunk_dims),
-            vec![80]
-        );
+        let g = ChunkGrid::fixed_array(&[100], None, &[20]).unwrap();
+        assert_eq!(g.offsets(0).unwrap(), vec![0]);
+        assert_eq!(g.offsets(1).unwrap(), vec![20]);
+        assert_eq!(g.offsets(4).unwrap(), vec![80]);
     }
 
     #[test]
     fn index_to_offsets_2d() {
-        let num_chunks = vec![3u64, 2];
-        let chunk_dims = vec![4u32, 3];
-        assert_eq!(
-            index_to_chunk_offsets(0, &num_chunks, &chunk_dims),
-            vec![0, 0]
-        );
-        assert_eq!(
-            index_to_chunk_offsets(1, &num_chunks, &chunk_dims),
-            vec![0, 3]
-        );
-        assert_eq!(
-            index_to_chunk_offsets(2, &num_chunks, &chunk_dims),
-            vec![4, 0]
-        );
+        let g = ChunkGrid::fixed_array(&[10, 6], None, &[4, 3]).unwrap();
+        assert_eq!(g.offsets(0).unwrap(), vec![0, 0]);
+        assert_eq!(g.offsets(1).unwrap(), vec![0, 3]);
+        assert_eq!(g.offsets(2).unwrap(), vec![4, 0]);
     }
 
     #[test]
@@ -734,6 +742,7 @@ mod tests {
         buf[44..52].copy_from_slice(&5u64.to_le_bytes()); // stat[4] = num_elements
         buf[52..60].copy_from_slice(&0u64.to_le_bytes()); // stat[5]
         buf[60..68].copy_from_slice(&0x1000u64.to_le_bytes()); // index_block_address
+        stamp_checksum(&mut buf, 0, 68);
 
         let hdr = ExtensibleArrayHeader::parse(&buf, 0, os, ls).unwrap();
         assert_eq!(hdr.client_id, 0);
@@ -775,7 +784,7 @@ mod tests {
             index_block_address: (usize::MAX - 4) as u64,
         };
         let buf = vec![0u8; 64];
-        let r = read_extensible_array_chunks(&buf, &header, &[100], &[20], 8, 8, 8);
+        let r = read_extensible_array_chunks(&buf, &header, &[100], None, &[20], 8, 8, 8);
         assert!(r.is_err());
     }
 
@@ -819,6 +828,7 @@ mod tests {
             .copy_from_slice(&(num_chunks as u64).to_le_bytes());
         file_data[aehd_offset + 60..aehd_offset + 68]
             .copy_from_slice(&(aeib_offset as u64).to_le_bytes());
+        stamp_checksum(&mut file_data, aehd_offset, aehd_offset + 68);
         // checksum (4 bytes at +68) — not validated
 
         // Build AEIB at aeib_offset
@@ -836,12 +846,37 @@ mod tests {
             let p = elem_start + i * osv;
             file_data[p..p + osv].copy_from_slice(&addr.to_le_bytes());
         }
+        // The index block's checksum covers its prefix, every inline element
+        // slot, and every data block and super block address slot:
+        // ndblk_addrs = 2 * (sup_blk_min_data_ptrs - 1), and the super block
+        // pointers make up the rest of nsblks levels.
+        let sup_ptrs = file_data[aehd_offset + 10] as usize;
+        let dmin = file_data[aehd_offset + 9] as usize;
+        let nsblks = 1 + 10 - dmin.trailing_zeros() as usize;
+        let ndblk_addrs = 2 * (sup_ptrs - 1);
+        // Levels consumed by those direct data blocks (1, 1, 2, 2, ... per level).
+        let mut consumed = 0usize;
+        let mut levels = 0usize;
+        while consumed < ndblk_addrs {
+            consumed += 1 << (levels / 2);
+            levels += 1;
+        }
+        let ib_end = elem_start + num_chunks * osv + (ndblk_addrs + nsblks - levels) * osv;
+        stamp_checksum(&mut file_data, aeib_offset, ib_end);
 
         let header = ExtensibleArrayHeader::parse(&file_data, aehd_offset, os, ls).unwrap();
         let ds_dims = vec![40u64]; // 2 chunks × 20 elements
         let chunk_dims = vec![20u32];
-        let chunks =
-            read_extensible_array_chunks(&file_data, &header, &ds_dims, &chunk_dims, 8, os, ls)
+        let chunks = read_extensible_array_chunks(
+            &file_data,
+            &header,
+            &ds_dims,
+            None,
+            &chunk_dims,
+            8,
+            os,
+            ls,
+        )
         .unwrap();
 
         assert_eq!(chunks.len(), 2);
@@ -885,6 +920,7 @@ mod tests {
         // idx_blk_addr at offset 12 + 6*8 = 60
         file_data[aehd_offset + 60..aehd_offset + 68]
             .copy_from_slice(&(aeib_offset as u64).to_le_bytes());
+        stamp_checksum(&mut file_data, aehd_offset, aehd_offset + 68);
 
         // AEIB
         file_data[aeib_offset..aeib_offset + 4].copy_from_slice(b"EAIB");
@@ -903,48 +939,62 @@ mod tests {
             pos += osv;
         }
 
-        // Direct data block addresses: first sb_level=0 has 1 dblk, sb_level=1 has 1 dblk
-        // Total direct dblks for sblk_min=2: 2^0 + 2^1 = 1 + 2 = 3 (oops)
-        // Actually: sblk_min levels. level 0: 2^0=1 dblk, level 1: 2^1=2 dblks => 3 dblks
-        // But we only have 2 remaining elements.
-        // dblk sizes: level 0: 1 dblk of min_dblk=2; level 1: 2 dblks of 2 each (nelmts doubles at level > 0)
-        // Wait, re-reading the code: at level 0, nelmts=min_dblk=2, 1 dblk.
-        // At level 1, 1 dblk, nelmts still 2 (doubles only at level > 0... but the code says
-        // `if sb_level > 0 { nelmts *= 2 }` after pushing). Let me re-check.
-        // After push at level 0: nelmts=2. Then if 0>0 false, no double. Push 1 dblk of 2.
-        // Level 1: ndblks=2. Push 2 dblks of 2. Then 1>0 true, nelmts=4.
-        // Total: 3 dblks with sizes [2, 2, 2]. Total = 6.
-        // We only need 2 more elements. So only the first dblk has data.
-        let n_direct_dblks = 3;
+        // Direct data block addresses. With sup_blk_min_data_ptrs = 2 the index
+        // block holds 2 * (2 - 1) = 2 of them, which are the data blocks of
+        // super block levels 0 and 1: one of `min_dblk_nelmts` elements, then
+        // one of twice that (ndblks = 2^(u/2), dblk_nelmts = 2^((u+1)/2) * min).
+        // Only the first is allocated here; the rest of the array is empty.
+        let ndblk_addrs = 2 * (sblk_min as usize - 1);
         file_data[pos..pos + osv].copy_from_slice(&(aedb_offset as u64).to_le_bytes());
         pos += osv;
-        // 2 more dblk addresses - undefined
-        for _ in 1..n_direct_dblks {
+        for _ in 1..ndblk_addrs {
             file_data[pos..pos + osv].copy_from_slice(&u64::MAX.to_le_bytes());
             pos += osv;
         }
+        // Super block addresses fill the remaining levels; all unallocated.
+        let nsblks = 1 + 10 - (min_dblk_nelmts as usize).trailing_zeros() as usize;
+        let mut consumed = 0usize;
+        let mut levels = 0usize;
+        while consumed < ndblk_addrs {
+            consumed += 1 << (levels / 2);
+            levels += 1;
+        }
+        for _ in 0..(nsblks - levels) {
+            file_data[pos..pos + osv].copy_from_slice(&u64::MAX.to_le_bytes());
+            pos += osv;
+        }
+        stamp_checksum(&mut file_data, aeib_offset, pos);
 
-        // EADB at aedb_offset (min_dblk_nelmts elements)
+        // EADB holding the first data block's `min_dblk_nelmts` elements.
         file_data[aedb_offset..aedb_offset + 4].copy_from_slice(b"EADB");
         file_data[aedb_offset + 4] = 0;
         file_data[aedb_offset + 5] = 0;
         file_data[aedb_offset + 6..aedb_offset + 14]
             .copy_from_slice(&(aehd_offset as u64).to_le_bytes());
-        // block_offset: ceil(max_nelmts_bits/8) = ceil(10/8) = 2 bytes
-        // block_offset = 0 for first data block
-        let blk_off_size = (10usize).div_ceil(8); // max_nelmts_bits=10
-        let mut dbpos = aedb_offset + 6 + osv + blk_off_size;
+        // Block offset field: ceil(max_nelmts_bits / 8) bytes, zero here.
+        let blk_off_size = (10usize).div_ceil(8);
+        let db_elems = aedb_offset + 6 + osv + blk_off_size;
+        let mut dbpos = db_elems;
         for i in 0..min_dblk_nelmts as usize {
             let addr = base_addr + (idx_blk_elmts as u64 + i as u64) * chunk_byte_size;
             file_data[dbpos..dbpos + osv].copy_from_slice(&addr.to_le_bytes());
             dbpos += osv;
         }
+        stamp_checksum(&mut file_data, aedb_offset, dbpos);
 
         let header = ExtensibleArrayHeader::parse(&file_data, aehd_offset, os, ls).unwrap();
         let ds_dims = vec![40u64];
         let chunk_dims = vec![10u32];
-        let chunks =
-            read_extensible_array_chunks(&file_data, &header, &ds_dims, &chunk_dims, 8, os, ls)
+        let chunks = read_extensible_array_chunks(
+            &file_data,
+            &header,
+            &ds_dims,
+            None,
+            &chunk_dims,
+            8,
+            os,
+            ls,
+        )
         .unwrap();
 
         assert_eq!(chunks.len(), 4);
@@ -967,10 +1017,8 @@ mod tests {
     #[test]
     fn read_element_unallocated() {
         let data = vec![0xFFu8; 16];
-        let num_chunks = vec![5u64];
-        let chunk_dims = vec![10u32];
-        let (info, consumed) =
-            read_element(&data, 0, 0, 8, 8, 80, 0, &num_chunks, &chunk_dims).unwrap();
+        let grid = ChunkGrid::fixed_array(&[50], None, &[10]).unwrap();
+        let (info, consumed) = read_element(&data, 0, 0, 8, 8, 80, 0, &grid).unwrap();
         assert!(info.is_none());
         assert_eq!(consumed, 8);
     }
@@ -989,20 +1037,9 @@ mod tests {
         // Filter mask
         data[12..16].copy_from_slice(&0u32.to_le_bytes());
 
-        let num_chunks = vec![5u64];
-        let chunk_dims = vec![10u32];
-        let (info, consumed) = read_element(
-            &data,
-            0,
-            1,
-            elem_size as u8,
-            os,
-            80,
-            2,
-            &num_chunks,
-            &chunk_dims,
-        )
-        .unwrap();
+        let grid = ChunkGrid::fixed_array(&[50], None, &[10]).unwrap();
+        let (info, consumed) =
+            read_element(&data, 0, 1, elem_size as u8, os, 80, 2, &grid).unwrap();
         let ci = info.unwrap();
         assert_eq!(ci.address, 0x2000);
         assert_eq!(ci.chunk_size, 120);

crates/clawhdf5-format/src/fill_value.rs

@@ -98,15 +98,50 @@ pub fn parse_fill_value(msg: &HeaderMessage) -> Result<Option<Vec<u8>>, FormatEr
 
 /// The fill value that applies to a dataset given its header messages. The new
 /// message wins over the old one when both are present.
+///
+/// A *shared* fill value message holds only a reference to the real message,
+/// which cannot be followed without the file: this returns
+/// [`FormatError::UnresolvedSharedMessage`] for one (it used to answer "zeros").
+/// Use [`dataset_fill_value_in`] when the file bytes are at hand.
 pub fn dataset_fill_value(messages: &[HeaderMessage]) -> Result<Option<Vec<u8>>, FormatError> {
+    fill_value_from(messages, |_| Err(FormatError::UnresolvedSharedMessage))
+}
+
+/// [`dataset_fill_value`] for a dataset in `file_data`, following a shared
+/// fill value message to where it lives: another object header, or the
+/// file's shared-message (SOHM) heap, as libhdf5 writes it when the file has
+/// a SOHM index for fill values.
+pub fn dataset_fill_value_in(
+    file_data: &[u8],
+    messages: &[HeaderMessage],
+    offset_size: u8,
+    length_size: u8,
+) -> Result<Option<Vec<u8>>, FormatError> {
+    fill_value_from(messages, |msg| {
+        crate::shared_message::message_data_with_sohm(file_data, msg, offset_size, length_size)
+            .map(|data| data.into_owned())
+    })
+}
+
+fn fill_value_from(
+    messages: &[HeaderMessage],
+    resolve_shared: impl Fn(&HeaderMessage) -> Result<Vec<u8>, FormatError>,
+) -> Result<Option<Vec<u8>>, FormatError> {
     for wanted in [MessageType::FillValue, MessageType::FillValueOld] {
         if let Some(msg) = messages.iter().find(|m| m.msg_type == wanted) {
-            if crate::shared_message::is_shared(msg.flags) {
-                // A shared fill value is legal but vanishingly rare; treat it
-                // as the default rather than misparsing the reference.
-                return Ok(None);
-            }
-            if let Some(value) = parse_fill_value(msg)? {
+            let value = if crate::shared_message::is_shared(msg.flags) {
+                let data = resolve_shared(msg)?;
+                parse_fill_value(&HeaderMessage {
+                    msg_type: msg.msg_type,
+                    size: data.len(),
+                    flags: msg.flags & !0x02,
+                    creation_order: msg.creation_order,
+                    data,
+                })?
+            } else {
+                parse_fill_value(msg)?
+            };
+            if let Some(value) = value {
                 return Ok(Some(value));
             }
         }
@@ -174,7 +209,7 @@ pub fn read_full_with_fill<E: From<FormatError>>(
     {
         return Err(FormatError::ExternalDataFilesUnsupported.into());
     }
-    let fill = dataset_fill_value(messages)?;
+    let fill = dataset_fill_value_in(file_data, messages, offset_size, length_size)?;
     if !has_storage(layout) {
         return Ok(filled_dataset(dataspace, elem_size, fill.as_deref())?);
     }

crates/clawhdf5-format/src/filter_pipeline.rs

@@ -19,8 +19,35 @@ pub const FILTER_SCALEOFFSET: u16 = 6;
 pub const FILTER_LZ4: u16 = 32004;
 /// Zstandard compression.
 pub const FILTER_ZSTD: u16 = 32015;
-/// Pcodec lossless numerical codec (clawhdf5 internal; not yet HDF5-registered).
-pub const FILTER_PCODEC: u16 = 32023;
+/// bzip2 (registered by PyTables; hdf5plugin's `BZip2`).
+pub const FILTER_BZIP2: u16 = 307;
+/// LZF — h5py's built-in `compression="lzf"`.
+pub const FILTER_LZF: u16 = 32000;
+/// Blosc 1 (hdf5-blosc; hdf5plugin's `Blosc`).
+pub const FILTER_BLOSC: u16 = 32001;
+/// Bitshuffle, optionally with LZ4 or Zstandard (hdf5plugin's `Bitshuffle`).
+pub const FILTER_BITSHUFFLE: u16 = 32008;
+/// ZFP lossy floating-point compression (hdf5plugin's `Zfp`). Not supported.
+pub const FILTER_ZFP: u16 = 32013;
+/// Blosc 2 (hdf5plugin's `Blosc2`).
+pub const FILTER_BLOSC2: u16 = 32026;
+/// Pcodec lossless numerical codec — a **private, unregistered** clawhdf5
+/// filter. Pcodec has no ID in the HDF Group's filter registry (checked
+/// 2026-09-25, `hdf5_plugins/docs/RegisteredFilterPlugins.md`), so it uses an
+/// ID from the registry's testing/private range (256–511). No libhdf5 plugin
+/// decodes it: h5py/libhdf5 report the filter as unavailable. Only clawhdf5
+/// (with the `pcodec` feature) reads these datasets.
+pub const FILTER_PCODEC: u16 = 480;
+/// Filter name written with [`FILTER_PCODEC`].
+pub const FILTER_PCODEC_NAME: &str = "pcodec (clawhdf5 private)";
+/// The ID clawhdf5 up to 2.7.0 wrote pcodec under. It is registered to
+/// Granular BitRound (GBR), whose decode is a pass-through, so libhdf5 with
+/// that plugin would have returned the compressed bytes as data. Read as
+/// pcodec only when the filter is named exactly [`FILTER_PCODEC_LEGACY_NAME`],
+/// the name those versions wrote; never written.
+pub const FILTER_PCODEC_LEGACY: u16 = 32023;
+/// The filter name clawhdf5 up to 2.7.0 wrote with [`FILTER_PCODEC_LEGACY`].
+pub const FILTER_PCODEC_LEGACY_NAME: &str = "pcodec";
 
 /// Description of a single filter in a pipeline.
 #[derive(Debug, Clone, PartialEq)]

crates/clawhdf5-format/src/filter_registry.rs

@@ -0,0 +1,477 @@
+//! Filter registry: every filter is looked up here by its HDF5 filter ID.
+//!
+//! Two tiers:
+//!
+//! * **Built-in filters** — a static table of the filters compiled into this
+//!   build: the HDF5 standard filters (deflate, shuffle, Fletcher32, szip,
+//!   N-Bit, scale-offset) and the plugin filters whose cargo features are
+//!   enabled (LZ4, Zstandard, pcodec, LZF, bitshuffle, bzip2, blosc).
+//!   [`builtin_filters`] lists them.
+//! * **Registered filters** (`std` only) — codecs the application supplies
+//!   for any other ID with [`register_filter`] (a [`FilterCodec`], or just a
+//!   decoding closure). A registered codec cannot shadow a built-in one,
+//!   except under 32023: that ID belongs to Granular BitRound, and the
+//!   built-in entry there only reads the pcodec chunks clawhdf5 <= 2.7.0
+//!   wrote (filter name `"pcodec"`), so a codec registered for 32023 handles
+//!   every other chunk with that ID, and writes.
+//!
+//! An ID in neither tier fails with [`FormatError::UnsupportedFilter`], as it
+//! always has.
+//!
+//! ```
+//! # #[cfg(feature = "std")] {
+//! use clawhdf5_format::filter_registry::{self, FilterContext};
+//! use clawhdf5_format::error::FormatError;
+//!
+//! // A toy filter in the private-use range: every byte XORed with 0x5A.
+//! filter_registry::register_filter(300, |input: &[u8], _ctx: &FilterContext<'_>| {
+//!     Ok::<_, FormatError>(input.iter().map(|b| b ^ 0x5A).collect())
+//! })
+//! .unwrap();
+//! assert!(filter_registry::is_filter_available(300));
+//! filter_registry::unregister_filter(300);
+//! # }
+//! ```
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
+#[cfg(not(feature = "std"))]
+use alloc::vec::Vec;
+
+use crate::error::FormatError;
+use crate::filter_pipeline::FilterDescription;
+
+/// What a codec is told about the filter it is applying.
+#[derive(Debug, Clone, Copy)]
+pub struct FilterContext<'a> {
+    /// The filter as recorded in the dataset's filter pipeline: its ID, name,
+    /// flags and client data (`cd_values`).
+    pub filter: &'a FilterDescription,
+    /// Size in bytes of one dataset element (the datatype's size).
+    pub element_size: usize,
+    /// Decoding only: the most bytes this stage may produce — what entered
+    /// the filter when the chunk was written. 0 means unknown; a decoder then
+    /// falls back to a fixed ceiling. Always 0 when encoding.
+    pub max_output: usize,
+}
+
+impl FilterContext<'_> {
+    /// The filter's client data (`cd_values`).
+    pub fn client_data(&self) -> &[u32] {
+        &self.filter.client_data
+    }
+
+    /// The largest output a decoder should allow: [`Self::max_output`], or
+    /// 256 MiB when that is unknown.
+    pub fn output_limit(&self) -> usize {
+        if self.max_output != 0 {
+            self.max_output
+        } else {
+            crate::filters::MAX_DECOMPRESS_SIZE
+        }
+    }
+}
+
+/// A filter implementation.
+///
+/// `decode` undoes the filter (the read direction). `encode` applies it (the
+/// write direction); the default refuses with
+/// [`FormatError::UnsupportedFilter`], which is right for a read-only codec.
+pub trait FilterCodec: Send + Sync {
+    /// Undo the filter on one chunk. The output must not exceed
+    /// [`FilterContext::output_limit`]; the pipeline rejects a larger one.
+    fn decode(&self, input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError>;
+
+    /// Apply the filter to one chunk.
+    fn encode(&self, input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+        let _ = input;
+        Err(FormatError::UnsupportedFilter(ctx.filter.filter_id))
+    }
+}
+
+/// Any `Fn(&[u8], &FilterContext) -> Result<Vec<u8>, FormatError>` is a
+/// decode-only codec.
+impl<F> FilterCodec for F
+where
+    F: Fn(&[u8], &FilterContext<'_>) -> Result<Vec<u8>, FormatError> + Send + Sync,
+{
+    fn decode(&self, input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+        self(input, ctx)
+    }
+}
+
+/// Signature of a built-in filter's decoder or encoder.
+pub type BuiltinFn = fn(&[u8], &FilterContext<'_>) -> Result<Vec<u8>, FormatError>;
+
+/// A filter compiled into this build.
+#[derive(Debug, Clone, Copy)]
+pub struct BuiltinFilter {
+    /// HDF5 filter ID.
+    pub id: u16,
+    /// Human-readable name.
+    pub name: &'static str,
+    /// Decoder.
+    pub(crate) decode: BuiltinFn,
+    /// Encoder, if this build can write the filter.
+    pub(crate) encode: Option<BuiltinFn>,
+}
+
+impl BuiltinFilter {
+    /// Whether this build can write the filter as well as read it.
+    pub fn can_encode(&self) -> bool {
+        self.encode.is_some()
+    }
+
+    /// Whether the built-in entry only borrows its ID for some chunks, so a
+    /// registered codec may take the rest: the legacy pcodec entry under
+    /// Granular BitRound's 32023, which claims only chunks named `"pcodec"`.
+    fn is_shared(&self) -> bool {
+        self.id == crate::filter_pipeline::FILTER_PCODEC_LEGACY
+    }
+
+    /// Whether this entry decodes chunks written with `filter`.
+    fn claims(&self, filter: &crate::filter_pipeline::FilterDescription) -> bool {
+        !self.is_shared()
+            || filter.name.as_deref() == Some(crate::filter_pipeline::FILTER_PCODEC_LEGACY_NAME)
+    }
+}
+
+/// The filters compiled into this build, in ID order.
+pub fn builtin_filters() -> &'static [BuiltinFilter] {
+    crate::filters::BUILTIN_FILTERS
+}
+
+/// The built-in filter with this ID, if it is compiled in.
+pub fn builtin_filter(id: u16) -> Option<&'static BuiltinFilter> {
+    builtin_filters().iter().find(|f| f.id == id)
+}
+
+/// Why a filter ID may be missing from this build: the filter's name, and
+/// the cargo feature that provides it (`None`: clawhdf5 does not implement
+/// it — register a codec for it with [`register_filter`]). `None` for an ID
+/// clawhdf5 knows nothing about.
+pub fn known_filter(id: u16) -> Option<(&'static str, Option<&'static str>)> {
+    Some(match id {
+        1 => ("deflate", Some("deflate")),
+        4 => ("SZIP", Some("szip")),
+        307 => ("bzip2", Some("bzip2")),
+        480 => ("pcodec", Some("pcodec")),
+        32000 => ("LZF", Some("lzf")),
+        32001 => ("Blosc", Some("blosc")),
+        32004 => ("LZ4", Some("lz4")),
+        32008 => ("bitshuffle", Some("bitshuffle")),
+        32013 => ("ZFP", None),
+        32015 => ("Zstandard", Some("zstd")),
+        32019 => ("JPEG", None),
+        32022 => ("BitGroom", None),
+        32023 => ("Granular BitRound", None),
+        32026 => ("Blosc2", None),
+        _ => return None,
+    })
+}
+
+/// Whether a chunk filtered with `id` can be decoded: a built-in filter or a
+/// registered one.
+pub fn is_filter_available(id: u16) -> bool {
+    if builtin_filter(id).is_some() {
+        return true;
+    }
+    #[cfg(feature = "std")]
+    {
+        registered(id).is_some()
+    }
+    #[cfg(not(feature = "std"))]
+    {
+        false
+    }
+}
+
+#[cfg(feature = "std")]
+mod custom {
+    use super::FilterCodec;
+    use std::collections::BTreeMap;
+    use std::sync::{Arc, PoisonError, RwLock};
+
+    pub(super) type Registry = BTreeMap<u16, Arc<dyn FilterCodec>>;
+
+    static REGISTRY: RwLock<Registry> = RwLock::new(BTreeMap::new());
+
+    pub(super) fn with_read<R>(f: impl FnOnce(&Registry) -> R) -> R {
+        // A panic while holding the lock cannot leave the map half-updated
+        // (every update is a single insert/remove), so poisoning is ignored.
+        f(&REGISTRY.read().unwrap_or_else(PoisonError::into_inner))
+    }
+
+    pub(super) fn with_write<R>(f: impl FnOnce(&mut Registry) -> R) -> R {
+        f(&mut REGISTRY.write().unwrap_or_else(PoisonError::into_inner))
+    }
+}
+
+/// Register a codec for filter `id`, process-wide. It is used for every
+/// chunk read (and, if it implements [`FilterCodec::encode`], written) with
+/// that filter ID, by every file.
+///
+/// A plain closure `Fn(&[u8], &FilterContext) -> Result<Vec<u8>, FormatError>`
+/// registers a decoder. Replaces (and returns) an earlier registration for
+/// the same ID. Fails with [`FormatError::FilterError`] if `id` is a built-in
+/// filter of this build: those cannot be overridden. The exception is 32023
+/// (Granular BitRound): with the `pcodec` feature the built-in entry there
+/// reads only chunks whose filter is named `"pcodec"` (clawhdf5 <= 2.7.0's
+/// files); a codec registered for 32023 decodes every other chunk with that
+/// ID and does all the writing.
+#[cfg(feature = "std")]
+pub fn register_filter<C>(
+    id: u16,
+    codec: C,
+) -> Result<Option<std::sync::Arc<dyn FilterCodec>>, FormatError>
+where
+    C: FilterCodec + 'static,
+{
+    if let Some(builtin) = builtin_filter(id).filter(|b| !b.is_shared()) {
+        return Err(FormatError::FilterError(format!(
+            "filter {id} ({}) is built in and cannot be re-registered",
+            builtin.name
+        )));
+    }
+    let codec: std::sync::Arc<dyn FilterCodec> = std::sync::Arc::new(codec);
+    Ok(custom::with_write(|r| r.insert(id, codec)))
+}
+
+/// Remove the codec registered for `id`. Returns whether one was registered.
+#[cfg(feature = "std")]
+pub fn unregister_filter(id: u16) -> bool {
+    custom::with_write(|r| r.remove(&id).is_some())
+}
+
+/// The codec registered for `id`, if any.
+#[cfg(feature = "std")]
+pub fn registered(id: u16) -> Option<std::sync::Arc<dyn FilterCodec>> {
+    custom::with_read(|r| r.get(&id).cloned())
+}
+
+/// Undo filter `ctx.filter` on `input`: the built-in decoder if there is one
+/// that claims the chunk, else a registered one, else the built-in decoder's
+/// own refusal or [`FormatError::UnsupportedFilter`].
+pub(crate) fn decode(input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    let id = ctx.filter.filter_id;
+    let builtin = builtin_filter(id);
+    if let Some(builtin) = builtin.filter(|b| b.claims(ctx.filter)) {
+        return (builtin.decode)(input, ctx);
+    }
+    #[cfg(feature = "std")]
+    if let Some(codec) = registered(id) {
+        let out = codec.decode(input, ctx)?;
+        // A registered codec is outside our control: hold it to the same
+        // bound the built-in decoders enforce.
+        if out.len() > ctx.output_limit() {
+            return Err(FormatError::DecompressionError(format!(
+                "filter {id}: decoded {} bytes, more than the {} the chunk can hold",
+                out.len(),
+                ctx.output_limit()
+            )));
+        }
+        return Ok(out);
+    }
+    match builtin {
+        Some(builtin) => (builtin.decode)(input, ctx),
+        None => Err(FormatError::UnsupportedFilter(id)),
+    }
+}
+
+/// Apply filter `ctx.filter` to `input`.
+pub(crate) fn encode(input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    let id = ctx.filter.filter_id;
+    #[cfg(feature = "std")]
+    if builtin_filter(id).is_some_and(|b| b.is_shared())
+        && let Some(codec) = registered(id)
+    {
+        return codec.encode(input, ctx);
+    }
+    if let Some(builtin) = builtin_filter(id) {
+        return match builtin.encode {
+            Some(encode) => encode(input, ctx),
+            None => Err(FormatError::UnsupportedFilter(id)),
+        };
+    }
+    #[cfg(feature = "std")]
+    if let Some(codec) = registered(id) {
+        return codec.encode(input, ctx);
+    }
+    Err(FormatError::UnsupportedFilter(id))
+}
+
+#[cfg(all(test, feature = "std"))]
+pub(crate) mod tests {
+    use super::*;
+    use crate::filter_pipeline::{FILTER_FLETCHER32, FILTER_SHUFFLE, FilterPipeline};
+    use crate::filters::{compress_chunk, decompress_chunk};
+
+    fn pipeline(id: u16) -> FilterPipeline {
+        FilterPipeline {
+            version: 2,
+            filters: vec![FilterDescription {
+                filter_id: id,
+                name: Some("test".into()),
+                flags: 0,
+                client_data: vec![7],
+            }],
+        }
+    }
+
+    struct Xor;
+    impl FilterCodec for Xor {
+        fn decode(&self, input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+            let k = ctx.client_data()[0] as u8;
+            Ok(input.iter().map(|b| b ^ k).collect())
+        }
+        fn encode(&self, input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+            self.decode(input, ctx)
+        }
+    }
+
+    // Each test uses its own ID: the registry is process-wide and tests run
+    // in parallel.
+
+    #[test]
+    fn unknown_filter_keeps_its_error() {
+        let err = decompress_chunk(b"abc", &pipeline(311), 3, 1).unwrap_err();
+        assert_eq!(err, FormatError::UnsupportedFilter(311));
+        let err = compress_chunk(b"abc", &pipeline(311), 1).unwrap_err();
+        assert_eq!(err, FormatError::UnsupportedFilter(311));
+    }
+
+    #[test]
+    fn registered_codec_round_trips_through_the_pipeline() {
+        assert!(!is_filter_available(312));
+        assert!(register_filter(312, Xor).unwrap().is_none());
+        assert!(is_filter_available(312));
+        let data = b"hello, registry".to_vec();
+        let enc = compress_chunk(&data, &pipeline(312), 1).unwrap();
+        assert_ne!(enc, data);
+        assert_eq!(
+            decompress_chunk(&enc, &pipeline(312), data.len(), 1).unwrap(),
+            data
+        );
+        assert!(unregister_filter(312));
+        assert!(!unregister_filter(312));
+        assert_eq!(
+            decompress_chunk(&enc, &pipeline(312), data.len(), 1).unwrap_err(),
+            FormatError::UnsupportedFilter(312)
+        );
+    }
+
+    #[test]
+    fn closure_registers_a_decoder_only() {
+        register_filter(313, |input: &[u8], _ctx: &FilterContext<'_>| {
+            Ok(input.iter().rev().copied().collect())
+        })
+        .unwrap();
+        assert_eq!(
+            decompress_chunk(b"abc", &pipeline(313), 3, 1).unwrap(),
+            b"cba"
+        );
+        assert_eq!(
+            compress_chunk(b"abc", &pipeline(313), 1).unwrap_err(),
+            FormatError::UnsupportedFilter(313)
+        );
+        unregister_filter(313);
+    }
+
+    #[test]
+    fn registered_decoder_output_is_bounded() {
+        register_filter(314, |_input: &[u8], _ctx: &FilterContext<'_>| {
+            Ok(vec![0u8; 1000])
+        })
+        .unwrap();
+        let err = decompress_chunk(b"abc", &pipeline(314), 10, 1).unwrap_err();
+        assert!(matches!(err, FormatError::DecompressionError(_)), "{err:?}");
+        unregister_filter(314);
+    }
+
+    #[test]
+    fn builtins_cannot_be_overridden() {
+        for id in [FILTER_SHUFFLE, FILTER_FLETCHER32] {
+            let Err(err) = register_filter(id, Xor) else {
+                panic!("built-in filter {id} was re-registered");
+            };
+            assert!(matches!(err, FormatError::FilterError(_)), "{err:?}");
+        }
+        assert!(builtin_filter(FILTER_SHUFFLE).is_some());
+    }
+
+    /// Serialises the tests that register or read filter 32023 (the
+    /// registry is process-wide).
+    pub(crate) static ID_32023: std::sync::Mutex<()> = std::sync::Mutex::new(());
+
+    /// 32023 is Granular BitRound's ID; the `pcodec` build's built-in entry
+    /// there reads only clawhdf5 <= 2.7.0's pcodec chunks (named "pcodec"),
+    /// so a codec can be registered for the rest, and writes with it.
+    #[test]
+    fn a_codec_can_be_registered_for_granular_bitround() {
+        let _guard = ID_32023
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner);
+        let named = |name: Option<&str>| FilterPipeline {
+            version: 2,
+            filters: vec![FilterDescription {
+                filter_id: 32023,
+                name: name.map(Into::into),
+                flags: 0,
+                client_data: vec![7],
+            }],
+        };
+        let prev = register_filter(32023, Xor).expect("32023 must be registrable");
+        assert!(prev.is_none());
+        let data = b"granular bitround".to_vec();
+        for name in [None, Some("granular_bitround"), Some("test")] {
+            let pl = named(name);
+            let enc = compress_chunk(&data, &pl, 1).unwrap();
+            assert_ne!(enc, data);
+            assert_eq!(decompress_chunk(&enc, &pl, data.len(), 1).unwrap(), data);
+        }
+        // clawhdf5 <= 2.7.0's pcodec chunks still go to the built-in reader.
+        #[cfg(feature = "pcodec")]
+        {
+            let raw: Vec<u8> = (0..64)
+                .flat_map(|i| (f64::from(i) * 0.5).to_le_bytes())
+                .collect();
+            let comp = crate::filters::pcodec_compress(&raw, 8).unwrap();
+            let mut pl = named(Some("pcodec"));
+            pl.filters[0].client_data = vec![8];
+            assert_eq!(decompress_chunk(&comp, &pl, raw.len(), 8).unwrap(), raw);
+        }
+        assert!(unregister_filter(32023));
+        let pl = named(None);
+        assert!(matches!(
+            decompress_chunk(&data, &pl, data.len(), 1),
+            Err(FormatError::UnsupportedFilter(32023))
+        ));
+    }
+
+    #[test]
+    fn unsupported_filter_error_names_the_filter() {
+        let msg = FormatError::UnsupportedFilter(32026).to_string();
+        assert!(
+            msg.contains("Blosc2") && msg.contains("not implemented"),
+            "{msg}"
+        );
+        let msg = FormatError::UnsupportedFilter(32013).to_string();
+        assert!(msg.contains("ZFP"), "{msg}");
+        let msg = FormatError::UnsupportedFilter(32000).to_string();
+        assert!(msg.contains("LZF") && msg.contains("`lzf`"), "{msg}");
+        assert_eq!(
+            FormatError::UnsupportedFilter(399).to_string(),
+            "unsupported filter: 399"
+        );
+    }
+
+    #[test]
+    fn builtin_table_is_sorted_and_unique() {
+        let ids: Vec<u16> = builtin_filters().iter().map(|f| f.id).collect();
+        let mut sorted = ids.clone();
+        sorted.sort_unstable();
+        sorted.dedup();
+        assert_eq!(ids, sorted);
+    }
+}

crates/clawhdf5-format/src/filters_bitshuffle.rs

@@ -0,0 +1,438 @@
+//! Bitshuffle (HDF5 filter 32008) and the bit transpose it shares with blosc.
+//!
+//! **The transform.** A block of `n` elements (`n` a multiple of 8) of
+//! `es` bytes each is viewed as an `n × 8·es` bit matrix — row *i* is
+//! element *i*, column `8·j + k` is bit *k* (LSB first) of its byte *j* — and
+//! transposed: the output is `8·es` rows of `n` bits, row `8·j + k` holding
+//! bit *k* of byte *j* of every element in order, packed LSB first. That is
+//! what `bshuf_trans_bit_elem` produces (checked against hdf5plugin's
+//! library bit for bit).
+//!
+//! **The filter** (`bshuf_h5filter.c`). `cd_values`: `[0..2]` bitshuffle
+//! version, `[2]` element size, `[3]` block size in elements (0 = default:
+//! 8192 bytes' worth, rounded down to a multiple of 8, at least 128),
+//! `[4]` compression (0 none, 2 LZ4, 3 Zstandard), `[5]` Zstandard level.
+//! The chunk is cut into blocks of `block size` elements; the tail shorter
+//! than a block is transposed as one block rounded down to a multiple of 8
+//! elements, and the last `n mod 8` elements are stored as they are.
+//! Uncompressed, that is the whole chunk. Compressed, the chunk starts with a
+//! 12-byte header — the decoded size (u64 big-endian) and the block size in
+//! bytes (u32 big-endian) — and each transposed block is stored as a u32
+//! big-endian length and an LZ4 block / Zstandard frame; the untransposed
+//! tail follows the last block.
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+#[cfg(not(feature = "std"))]
+use alloc::{format, vec, vec::Vec};
+
+use crate::error::FormatError;
+#[cfg(feature = "bitshuffle")]
+use crate::filter_registry::FilterContext;
+
+/// Transpose an 8×8 bit matrix packed in a u64 (byte *r* = row *r*, bit *c*
+/// of that byte = column *c*). An involution.
+#[inline]
+fn transpose8(mut x: u64) -> u64 {
+    let t = (x ^ (x >> 7)) & 0x00AA_00AA_00AA_00AA;
+    x = x ^ t ^ (t << 7);
+    let t = (x ^ (x >> 14)) & 0x0000_CCCC_0000_CCCC;
+    x = x ^ t ^ (t << 14);
+    let t = (x ^ (x >> 28)) & 0x0000_0000_F0F0_F0F0;
+    x ^ t ^ (t << 28)
+}
+
+/// Bit-transpose one block: `input` and `out` are `n * es` bytes, `n` a
+/// multiple of 8.
+pub(crate) fn bitshuffle_block(input: &[u8], out: &mut [u8], n: usize, es: usize) {
+    debug_assert!(n.is_multiple_of(8) && input.len() == n * es && out.len() == n * es);
+    let row = n / 8;
+    for j in 0..es {
+        for g in 0..row {
+            let mut x = 0u64;
+            for t in 0..8 {
+                x |= u64::from(input[(8 * g + t) * es + j]) << (8 * t);
+            }
+            let y = transpose8(x);
+            for k in 0..8 {
+                out[(8 * j + k) * row + g] = (y >> (8 * k)) as u8;
+            }
+        }
+    }
+}
+
+/// Undo [`bitshuffle_block`].
+pub(crate) fn bitunshuffle_block(input: &[u8], out: &mut [u8], n: usize, es: usize) {
+    debug_assert!(n.is_multiple_of(8) && input.len() == n * es && out.len() == n * es);
+    let row = n / 8;
+    for j in 0..es {
+        for g in 0..row {
+            let mut y = 0u64;
+            for k in 0..8 {
+                y |= u64::from(input[(8 * j + k) * row + g]) << (8 * k);
+            }
+            let x = transpose8(y);
+            for t in 0..8 {
+                out[(8 * g + t) * es + j] = (x >> (8 * t)) as u8;
+            }
+        }
+    }
+}
+
+/// `bshuf_default_block_size`: 8 KiB of elements, a multiple of 8, >= 128.
+#[cfg(feature = "bitshuffle")]
+fn default_block_size(es: usize) -> usize {
+    ((8192 / es) / 8 * 8).max(128)
+}
+
+#[cfg(feature = "bitshuffle")]
+fn err(msg: &str) -> FormatError {
+    FormatError::DecompressionError(format!("bitshuffle: {msg}"))
+}
+
+/// `cd_values[4]`: the compression bitshuffle applies after the transpose.
+#[cfg(feature = "bitshuffle")]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Codec {
+    None,
+    Lz4,
+    Zstd,
+}
+
+#[cfg(feature = "bitshuffle")]
+fn codec(cd: &[u32]) -> Result<Codec, FormatError> {
+    match cd.get(4).copied().unwrap_or(0) {
+        0 => Ok(Codec::None),
+        2 => Ok(Codec::Lz4),
+        3 => Ok(Codec::Zstd),
+        other => Err(FormatError::FilterError(format!(
+            "bitshuffle: unknown compression {other}"
+        ))),
+    }
+}
+
+/// The element counts of the transposed blocks for `size` elements.
+#[cfg(feature = "bitshuffle")]
+fn blocks(size: usize, block: usize) -> impl Iterator<Item = usize> {
+    let full = size / block;
+    let last = (size % block) / 8 * 8;
+    core::iter::repeat_n(block, full).chain((last > 0).then_some(last))
+}
+
+/// Decode a bitshuffle-filtered chunk.
+#[cfg(feature = "bitshuffle")]
+pub(crate) fn bitshuffle_decode(
+    input: &[u8],
+    ctx: &FilterContext<'_>,
+) -> Result<Vec<u8>, FormatError> {
+    let cd = ctx.client_data();
+    let es = match cd.get(2) {
+        Some(&e) if e != 0 => e as usize,
+        _ => return Err(err("missing element size")),
+    };
+    let codec = codec(cd)?;
+    let limit = ctx.output_limit();
+    if codec == Codec::None {
+        if input.len() > limit {
+            return Err(err("output exceeds the chunk size"));
+        }
+        let block = match cd.get(3) {
+            Some(&b) if b != 0 => b as usize,
+            _ => default_block_size(es),
+        };
+        if !block.is_multiple_of(8) {
+            return Err(err("block size is not a multiple of 8"));
+        }
+        if !input.len().is_multiple_of(es) {
+            return Err(err("chunk is not a whole number of elements"));
+        }
+        let size = input.len() / es;
+        let mut out = vec![0u8; input.len()];
+        let mut pos = 0;
+        for n in blocks(size, block) {
+            let bytes = n * es;
+            bitunshuffle_block(&input[pos..pos + bytes], &mut out[pos..pos + bytes], n, es);
+            pos += bytes;
+        }
+        out[pos..].copy_from_slice(&input[pos..]);
+        return Ok(out);
+    }
+
+    let header = input.get(..12).ok_or_else(|| err("truncated header"))?;
+    let total = u64::from_be_bytes(header[..8].try_into().unwrap());
+    let block_bytes = u32::from_be_bytes(header[8..12].try_into().unwrap()) as usize;
+    let total = usize::try_from(total)
+        .ok()
+        .filter(|&t| t <= limit)
+        .ok_or_else(|| err("decoded size exceeds the chunk size"))?;
+    if !total.is_multiple_of(es) {
+        return Err(err("chunk is not a whole number of elements"));
+    }
+    if block_bytes == 0 || !block_bytes.is_multiple_of(es) {
+        return Err(err("bad block size"));
+    }
+    let block = block_bytes / es;
+    if !block.is_multiple_of(8) {
+        return Err(err("block size is not a multiple of 8"));
+    }
+    let size = total / es;
+    let mut out = vec![0u8; total];
+    let mut tmp = vec![0u8; block_bytes.min(total)];
+    let mut ip = 12usize;
+    let mut op = 0usize;
+    let mut zstd = None;
+    for n in blocks(size, block) {
+        let bytes = n * es;
+        let len = input
+            .get(ip..ip + 4)
+            .map(|b| u32::from_be_bytes(b.try_into().unwrap()) as usize)
+            .ok_or_else(|| err("truncated block header"))?;
+        ip += 4;
+        let comp = input
+            .get(ip..ip.saturating_add(len))
+            .ok_or_else(|| err("truncated block"))?;
+        ip += len;
+        let dst = &mut tmp[..bytes];
+        let got = match codec {
+            Codec::Lz4 => lz4_flex::block::decompress_into(comp, dst)
+                .map_err(|e| err(&format!("lz4: {e}")))?,
+            Codec::Zstd => zstd_decode_into(
+                zstd.get_or_insert_with(ruzstd::decoding::FrameDecoder::new),
+                comp,
+                dst,
+            )?,
+            Codec::None => unreachable!(),
+        };
+        if got != bytes {
+            return Err(err("block decoded to the wrong size"));
+        }
+        bitunshuffle_block(dst, &mut out[op..op + bytes], n, es);
+        op += bytes;
+    }
+    let tail = total - op;
+    let rest = input
+        .get(ip..ip + tail)
+        .ok_or_else(|| err("truncated trailing elements"))?;
+    out[op..].copy_from_slice(rest);
+    Ok(out)
+}
+
+/// Decode Zstandard frames into exactly `dst`, failing if they hold more.
+#[cfg(any(feature = "bitshuffle", feature = "blosc"))]
+pub(crate) fn zstd_decode_into(
+    decoder: &mut ruzstd::decoding::FrameDecoder,
+    frames: &[u8],
+    dst: &mut [u8],
+) -> Result<usize, FormatError> {
+    decoder
+        .decode_all(frames, dst)
+        .map_err(|e| FormatError::DecompressionError(format!("zstd: {e}")))
+}
+
+/// Compress with ruzstd. It implements one level (roughly zstd's level 1),
+/// so the requested level only matters to other encoders.
+#[cfg(any(feature = "bitshuffle", feature = "blosc"))]
+pub(crate) fn zstd_encode(data: &[u8]) -> Vec<u8> {
+    ruzstd::encoding::compress_to_vec(data, ruzstd::encoding::CompressionLevel::Fastest)
+}
+
+/// Encode a chunk with the bitshuffle filter.
+#[cfg(feature = "bitshuffle")]
+pub(crate) fn bitshuffle_encode(
+    input: &[u8],
+    ctx: &FilterContext<'_>,
+) -> Result<Vec<u8>, FormatError> {
+    let cd = ctx.client_data();
+    let es = match cd.get(2) {
+        Some(&e) if e != 0 => e as usize,
+        _ => ctx.element_size.max(1),
+    };
+    let codec = codec(cd)?;
+    let block = match cd.get(3) {
+        Some(&b) if b != 0 => b as usize,
+        _ => default_block_size(es),
+    };
+    let cerr = |m: &str| FormatError::CompressionError(format!("bitshuffle: {m}"));
+    if !block.is_multiple_of(8) {
+        return Err(cerr("block size is not a multiple of 8"));
+    }
+    if !input.len().is_multiple_of(es) {
+        return Err(cerr("chunk is not a whole number of elements"));
+    }
+    let size = input.len() / es;
+    let mut out = Vec::with_capacity(input.len() + 12 + input.len() / 64);
+    if codec != Codec::None {
+        out.extend_from_slice(&(input.len() as u64).to_be_bytes());
+        let block_bytes =
+            u32::try_from(block * es).map_err(|_| cerr("block size does not fit in 32 bits"))?;
+        out.extend_from_slice(&block_bytes.to_be_bytes());
+    }
+    let mut tmp = vec![0u8; (block * es).min(input.len())];
+    let mut pos = 0;
+    for n in blocks(size, block) {
+        let bytes = n * es;
+        let dst = &mut tmp[..bytes];
+        bitshuffle_block(&input[pos..pos + bytes], dst, n, es);
+        match codec {
+            Codec::None => out.extend_from_slice(dst),
+            Codec::Lz4 | Codec::Zstd => {
+                let comp = if codec == Codec::Lz4 {
+                    lz4_flex::block::compress(dst)
+                } else {
+                    zstd_encode(dst)
+                };
+                out.extend_from_slice(&(comp.len() as u32).to_be_bytes());
+                out.extend_from_slice(&comp);
+            }
+        }
+        pos += bytes;
+    }
+    out.extend_from_slice(&input[pos..]);
+    Ok(out)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// The definition, one bit at a time.
+    fn naive(input: &[u8], n: usize, es: usize) -> Vec<u8> {
+        let mut out = vec![0u8; n * es];
+        for i in 0..n {
+            for j in 0..es {
+                for k in 0..8 {
+                    if input[i * es + j] >> k & 1 == 1 {
+                        let p = (8 * j + k) * n + i;
+                        out[p / 8] |= 1 << (p % 8);
+                    }
+                }
+            }
+        }
+        out
+    }
+
+    #[test]
+    fn transpose_matches_the_definition_and_inverts() {
+        for (n, es) in [(8, 1), (16, 2), (24, 4), (128, 8), (64, 3), (8, 16)] {
+            let input: Vec<u8> = (0..n * es)
+                .map(|i| (i as u32).wrapping_mul(2_654_435_761).rotate_left(7) as u8)
+                .collect();
+            let mut out = vec![0u8; n * es];
+            bitshuffle_block(&input, &mut out, n, es);
+            assert_eq!(out, naive(&input, n, es), "n={n} es={es}");
+            let mut back = vec![0u8; n * es];
+            bitunshuffle_block(&out, &mut back, n, es);
+            assert_eq!(back, input);
+        }
+    }
+
+    #[cfg(feature = "bitshuffle")]
+    fn ctx_for(cd: Vec<u32>) -> crate::filter_pipeline::FilterDescription {
+        crate::filter_pipeline::FilterDescription {
+            filter_id: crate::filter_pipeline::FILTER_BITSHUFFLE,
+            name: None,
+            flags: 0,
+            client_data: cd,
+        }
+    }
+
+    #[cfg(feature = "bitshuffle")]
+    #[test]
+    fn filter_round_trips_every_mode() {
+        for es in [1usize, 2, 4, 8] {
+            for n in [0usize, 1, 7, 8, 100, 1000, 5003] {
+                let data: Vec<u8> = (0..n * es)
+                    .map(|i| (i % 97) as u8 ^ (i / 300) as u8)
+                    .collect();
+                for (comp, block) in [(0, 0), (0, 16), (2, 0), (2, 64), (3, 0), (3, 1024)] {
+                    let f = ctx_for(vec![0, 4, es as u32, block, comp]);
+                    let ctx = FilterContext {
+                        filter: &f,
+                        element_size: es,
+                        max_output: data.len(),
+                    };
+                    let enc = bitshuffle_encode(&data, &ctx).unwrap();
+                    let dec = bitshuffle_decode(&enc, &ctx).unwrap();
+                    assert_eq!(dec, data, "es={es} n={n} comp={comp} block={block}");
+                }
+            }
+        }
+    }
+
+    #[cfg(feature = "bitshuffle")]
+    #[test]
+    fn rejects_oversized_and_truncated_chunks() {
+        let data = vec![5u8; 4096];
+        let f = ctx_for(vec![0, 4, 4, 0, 2]);
+        let mut ctx = FilterContext {
+            filter: &f,
+            element_size: 4,
+            max_output: data.len(),
+        };
+        let enc = bitshuffle_encode(&data, &ctx).unwrap();
+        assert!(bitshuffle_decode(&enc[..enc.len() - 1], &ctx).is_err());
+        ctx.max_output = 100;
+        assert!(bitshuffle_decode(&enc, &ctx).is_err());
+    }
+
+    /// Random and mutated chunks, in every mode, and hostile `cd_values`:
+    /// errors are fine, panics are not.
+    #[cfg(feature = "bitshuffle")]
+    #[test]
+    fn fuzzed_chunks_never_panic() {
+        use crate::test_fuzz::{Rng, fuzz_decoder};
+        let data: Vec<u8> = (0..3001u32)
+            .flat_map(|i| ((i / 7) as u16).to_le_bytes())
+            .collect();
+        for (comp, block) in [(0, 0), (0, 16), (2, 0), (2, 64), (3, 0), (3, 1024)] {
+            let f = ctx_for(vec![0, 4, 2, block, comp]);
+            let ctx = FilterContext {
+                filter: &f,
+                element_size: 2,
+                max_output: data.len(),
+            };
+            let seeds = vec![
+                bitshuffle_encode(&data, &ctx).unwrap(),
+                bitshuffle_encode(&data[..34], &ctx).unwrap(),
+                bitshuffle_encode(&data[..512], &ctx).unwrap(),
+            ];
+            fuzz_decoder(
+                0xb5 + comp as u64 * 7 + block as u64,
+                &seeds,
+                4_000,
+                data.len(),
+                |s| bitshuffle_decode(s, &ctx),
+            );
+        }
+        // Hostile filter parameters on a valid chunk.
+        let mut rng = Rng::new(0xcd);
+        let good = ctx_for(vec![0, 4, 2, 0, 2]);
+        let enc = bitshuffle_encode(
+            &data,
+            &FilterContext {
+                filter: &good,
+                element_size: 2,
+                max_output: data.len(),
+            },
+        )
+        .unwrap();
+        for _ in 0..3_000 {
+            let cd: Vec<u32> = (0..rng.below(7))
+                .map(|_| match rng.below(4) {
+                    0 => rng.below(5) as u32,
+                    1 => u32::MAX - rng.below(4) as u32,
+                    2 => 1 << rng.below(32),
+                    _ => rng.next_u64() as u32,
+                })
+                .collect();
+            let f = ctx_for(cd);
+            let ctx = FilterContext {
+                filter: &f,
+                element_size: 2,
+                max_output: data.len(),
+            };
+            let _ = bitshuffle_decode(&enc, &ctx);
+            let _ = bitshuffle_decode(&data, &ctx);
+        }
+    }
+}

crates/clawhdf5-format/src/filters_blosc.rs

@@ -0,0 +1,711 @@
+//! Blosc 1 (HDF5 filter 32001, `hdf5-blosc`, hdf5plugin's `Blosc`), in pure
+//! Rust: the Blosc 1 frame, its byte shuffle and bit shuffle, and the
+//! BloscLZ, LZ4/LZ4HC, Snappy, Zlib and Zstandard codecs inside it.
+//!
+//! **Frame** (c-blosc 1.x, format version 2). A 16-byte header — version
+//! (2), codec format version (1), flags, type size, then little-endian `u32`
+//! decoded size, block size and frame size. Flags: bit 0 byte shuffle, bit
+//! 1 stored raw ("memcpyed": the data follows the header), bit 2 bit
+//! shuffle, bit 4 "do not split", bits 5-7 the codec (0 BloscLZ, 1 LZ4 and
+//! LZ4HC, 2 Snappy, 3 Zlib, 4 Zstandard). Unless stored raw, a table of
+//! `u32` block offsets follows, one per block of `block size` bytes (the
+//! last one may be shorter). A block is one stream, or — when the "do not
+//! split" flag is clear, the type size is at most 16, the block holds at
+//! least 128 elements, and it is not the short last block — `type size`
+//! streams, one per byte plane. Each stream is a `u32` length and the
+//! codec's output; a length equal to the stream's decoded size means the
+//! bytes are stored raw. The decoded block is then unshuffled (byte shuffle
+//! for type size > 1; bit shuffle when the block holds a multiple of 8
+//! elements, the trailing partial element copied as is).
+//!
+//! **Filter** (`blosc_filter.c`) `cd_values`: `[0]` filter revision, `[1]`
+//! Blosc format version, `[2]` type size, `[3]` chunk size in bytes, `[4]`
+//! compression level, `[5]` shuffle (0 none, 1 byte, 2 bit), `[6]`
+//! compressor (0 blosclz, 1 lz4, 2 lz4hc, 3 snappy, 4 zlib, 5 zstd). The
+//! decoder needs only the frame.
+
+use crate::error::FormatError;
+use crate::filter_registry::FilterContext;
+use crate::filters_bitshuffle::{bitshuffle_block, bitunshuffle_block};
+
+const HEADER: usize = 16;
+const FLAG_SHUFFLE: u8 = 0x01;
+const FLAG_MEMCPYED: u8 = 0x02;
+const FLAG_BITSHUFFLE: u8 = 0x04;
+const FLAG_FUTURE: u8 = 0x08;
+const FLAG_DONT_SPLIT: u8 = 0x10;
+const MAX_SPLITS: usize = 16;
+const MIN_BUFFERSIZE: usize = 128;
+
+fn err(msg: &str) -> FormatError {
+    FormatError::DecompressionError(format!("blosc: {msg}"))
+}
+
+fn le32(b: &[u8], at: usize) -> Result<usize, FormatError> {
+    b.get(at..at + 4)
+        .map(|s| u32::from_le_bytes(s.try_into().unwrap()) as usize)
+        .ok_or_else(|| err("truncated frame"))
+}
+
+/// The codec inside a Blosc frame (flags bits 5-7).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Codec {
+    BloscLz,
+    Lz4,
+    Snappy,
+    Zlib,
+    Zstd,
+}
+
+impl Codec {
+    fn from_flags(flags: u8) -> Result<Codec, FormatError> {
+        match flags >> 5 {
+            0 => Ok(Codec::BloscLz),
+            1 => Ok(Codec::Lz4),
+            2 => Ok(Codec::Snappy),
+            3 => Ok(Codec::Zlib),
+            4 => Ok(Codec::Zstd),
+            other => Err(err(&format!("unknown codec {other}"))),
+        }
+    }
+}
+
+/// Decode one codec stream into exactly `dst`.
+fn decode_stream(
+    codec: Codec,
+    src: &[u8],
+    dst: &mut [u8],
+    zstd: &mut Option<ruzstd::decoding::FrameDecoder>,
+) -> Result<(), FormatError> {
+    let n = match codec {
+        Codec::BloscLz => blosclz_decompress(src, dst),
+        Codec::Lz4 => {
+            lz4_flex::block::decompress_into(src, dst).map_err(|e| err(&format!("lz4: {e}")))?
+        }
+        Codec::Snappy => {
+            let len = snap::raw::decompress_len(src).map_err(|e| err(&format!("snappy: {e}")))?;
+            if len != dst.len() {
+                return Err(err("snappy stream has the wrong size"));
+            }
+            snap::raw::Decoder::new()
+                .decompress(src, dst)
+                .map_err(|e| err(&format!("snappy: {e}")))?
+        }
+        Codec::Zlib => {
+            let out = crate::filters::inflate_bounded(src, dst.len(), dst.len())
+                .map_err(|e| err(&format!("zlib: {e}")))?;
+            let n = out.len();
+            if n == dst.len() {
+                dst.copy_from_slice(&out);
+            }
+            n
+        }
+        Codec::Zstd => crate::filters_bitshuffle::zstd_decode_into(
+            zstd.get_or_insert_with(ruzstd::decoding::FrameDecoder::new),
+            src,
+            dst,
+        )?,
+    };
+    if n != dst.len() {
+        return Err(err("stream decoded to the wrong size"));
+    }
+    Ok(())
+}
+
+/// Decode a Blosc-filtered chunk: one Blosc 1 frame.
+///
+/// An HDF5 chunk is never empty, so a frame that decodes to nothing where
+/// the chunk size is known is corrupt (libhdf5's filter fails it too).
+pub(crate) fn blosc_decode(input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    let out = blosc_decompress(input, ctx.output_limit())?;
+    if out.is_empty() && ctx.max_output != 0 {
+        return Err(err("empty frame for a non-empty chunk"));
+    }
+    Ok(out)
+}
+
+/// Decompress a Blosc 1 frame, refusing more than `limit` bytes of output.
+pub fn blosc_decompress(input: &[u8], limit: usize) -> Result<Vec<u8>, FormatError> {
+    if input.len() < HEADER {
+        return Err(err("truncated header"));
+    }
+    let version = input[0];
+    let codec_version = input[1];
+    let flags = input[2];
+    let typesize = input[3] as usize;
+    let nbytes = le32(input, 4)?;
+    let blocksize = le32(input, 8)?;
+    let cbytes = le32(input, 12)?;
+    if version != 1 && version != 2 {
+        return Err(err(&format!(
+            "frame format version {version} is not Blosc 1 (a Blosc 2 chunk?)"
+        )));
+    }
+    if flags & FLAG_FUTURE != 0 {
+        return Err(err("unknown header flags"));
+    }
+    if nbytes > limit {
+        return Err(err("decoded size exceeds the chunk size"));
+    }
+    if cbytes > input.len() {
+        return Err(err("frame is longer than the chunk"));
+    }
+    if cbytes < HEADER {
+        return Err(err("truncated frame"));
+    }
+    let src = &input[..cbytes];
+    if nbytes == 0 {
+        return Ok(Vec::new());
+    }
+    if blocksize == 0 || typesize == 0 {
+        return Err(err("bad block or type size"));
+    }
+    let mut out = vec![0u8; nbytes];
+    if flags & FLAG_MEMCPYED != 0 {
+        if cbytes != nbytes + HEADER {
+            return Err(err("stored frame has the wrong size"));
+        }
+        out.copy_from_slice(&src[HEADER..]);
+        return Ok(out);
+    }
+    let codec = Codec::from_flags(flags)?;
+    if codec_version != 1 {
+        return Err(err(&format!(
+            "unsupported {codec:?} format version {codec_version}"
+        )));
+    }
+    let nblocks = nbytes.div_ceil(blocksize);
+    let leftover = nbytes % blocksize;
+    if nblocks > (cbytes - HEADER) / 4 {
+        return Err(err("block table is truncated"));
+    }
+    let block_len = blocksize.min(nbytes);
+    let mut tmp = vec![0u8; block_len];
+    let mut zstd = None;
+    let dont_split = flags & FLAG_DONT_SPLIT != 0;
+    for j in 0..nblocks {
+        let is_leftover = j == nblocks - 1 && leftover > 0;
+        let bsize = if is_leftover { leftover } else { blocksize };
+        let nsplits = if !dont_split
+            && typesize <= MAX_SPLITS
+            && bsize / typesize >= MIN_BUFFERSIZE
+            && !is_leftover
+        {
+            typesize
+        } else {
+            1
+        };
+        let neblock = bsize / nsplits;
+        let mut pos = le32(src, HEADER + 4 * j)?;
+        let tmp = &mut tmp[..bsize];
+        for s in 0..nsplits {
+            let clen = src
+                .get(pos..)
+                .and_then(|rest| rest.get(..4))
+                .map(|b| u32::from_le_bytes(b.try_into().unwrap()) as usize)
+                .ok_or_else(|| err("block offset out of range"))?;
+            pos += 4;
+            let stream = src
+                .get(pos..pos.saturating_add(clen))
+                .ok_or_else(|| err("stream runs past the frame"))?;
+            let dst = &mut tmp[s * neblock..(s + 1) * neblock];
+            if clen == neblock {
+                dst.copy_from_slice(stream);
+            } else {
+                decode_stream(codec, stream, dst, &mut zstd)?;
+            }
+            pos += clen;
+        }
+        // `bsize` is a whole number of splits by construction (`nsplits` > 1
+        // only for full blocks, and c-blosc sizes those in whole elements).
+        if nsplits * neblock != bsize {
+            return Err(err("block is not a whole number of streams"));
+        }
+        let dest = &mut out[j * blocksize..j * blocksize + bsize];
+        unshuffle_block(flags, typesize, tmp, dest);
+    }
+    Ok(out)
+}
+
+/// Undo the frame's shuffle on one decoded block.
+fn unshuffle_block(flags: u8, typesize: usize, src: &[u8], dest: &mut [u8]) {
+    let bsize = src.len();
+    if flags & FLAG_SHUFFLE != 0 && typesize > 1 {
+        let n = bsize / typesize;
+        for i in 0..n {
+            for b in 0..typesize {
+                dest[i * typesize + b] = src[b * n + i];
+            }
+        }
+        dest[n * typesize..].copy_from_slice(&src[n * typesize..]);
+    } else if flags & FLAG_BITSHUFFLE != 0 && bsize >= typesize {
+        let n = bsize / typesize;
+        if n.is_multiple_of(8) {
+            let body = n * typesize;
+            bitunshuffle_block(&src[..body], &mut dest[..body], n, typesize);
+            dest[body..].copy_from_slice(&src[body..]);
+        } else {
+            dest.copy_from_slice(src);
+        }
+    } else {
+        dest.copy_from_slice(src);
+    }
+}
+
+/// BloscLZ decompression (c-blosc 1.21 `blosclz_decompress`): returns the
+/// number of bytes written, or 0 on malformed input — exactly as the C
+/// decoder, including stopping before a match that ends the stream, so a
+/// stream libblosc rejects is rejected here too.
+///
+/// Instructions: a control byte `ctrl`. Below 32, a literal run of
+/// `ctrl + 1` bytes. Otherwise a match: length `(ctrl >> 5) + 2`, extended
+/// by following bytes while they are 255 when the top three bits are all
+/// set; distance `((ctrl & 31) << 8) + next byte + 1`, or — when that byte
+/// is 255 and the high bits are 31 — a 16-bit big-endian distance plus 8192.
+/// The first instruction is always a literal.
+pub(crate) fn blosclz_decompress(input: &[u8], out: &mut [u8]) -> usize {
+    const MAX_DISTANCE: usize = 8191;
+    let limit = input.len();
+    if limit == 0 {
+        return 0;
+    }
+    let mut ip = 1usize;
+    let mut op = 0usize;
+    let mut ctrl = (input[0] & 31) as usize;
+    loop {
+        if ctrl >= 32 {
+            let mut len = (ctrl >> 5) - 1;
+            let ofs = (ctrl & 31) << 8;
+            if len == 6 {
+                loop {
+                    if ip + 1 >= limit {
+                        return 0;
+                    }
+                    let code = input[ip] as usize;
+                    ip += 1;
+                    len += code;
+                    if code != 255 {
+                        break;
+                    }
+                }
+            } else if ip + 1 >= limit {
+                return 0;
+            }
+            let code = input[ip] as usize;
+            ip += 1;
+            len += 3;
+            // The copy source is `distance` bytes back.
+            let mut distance = ofs + code + 1;
+            if code == 255 && ofs == 31 << 8 {
+                if ip + 1 >= limit {
+                    return 0;
+                }
+                let far = ((input[ip] as usize) << 8) + input[ip + 1] as usize;
+                ip += 2;
+                distance = far + MAX_DISTANCE + 1;
+            }
+            if op + len > out.len() {
+                return 0;
+            }
+            if distance > op {
+                return 0;
+            }
+            if ip >= limit {
+                break;
+            }
+            ctrl = input[ip] as usize;
+            ip += 1;
+            let start = op - distance;
+            if distance >= len {
+                out.copy_within(start..start + len, op);
+            } else {
+                for k in 0..len {
+                    out[op + k] = out[start + k];
+                }
+            }
+            op += len;
+        } else {
+            let run = ctrl + 1;
+            if op + run > out.len() || ip + run > limit {
+                return 0;
+            }
+            out[op..op + run].copy_from_slice(&input[ip..ip + run]);
+            op += run;
+            ip += run;
+            if ip >= limit {
+                break;
+            }
+            ctrl = input[ip] as usize;
+            ip += 1;
+        }
+    }
+    op
+}
+
+/// The codec our encoder puts inside the frame.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum EncodeCodec {
+    Lz4,
+    Snappy,
+    Zlib,
+    Zstd,
+}
+
+impl EncodeCodec {
+    /// From the filter's `cd_values[6]` compressor code.
+    fn from_cd(code: u32) -> Result<EncodeCodec, FormatError> {
+        match code {
+            1 | 2 => Ok(EncodeCodec::Lz4),
+            3 => Ok(EncodeCodec::Snappy),
+            4 => Ok(EncodeCodec::Zlib),
+            5 => Ok(EncodeCodec::Zstd),
+            0 => Err(FormatError::CompressionError(
+                "blosc: clawhdf5 cannot write BloscLZ; choose lz4, snappy, zlib or zstd".into(),
+            )),
+            other => Err(FormatError::CompressionError(format!(
+                "blosc: unknown compressor {other}"
+            ))),
+        }
+    }
+
+    fn flags(self) -> u8 {
+        (match self {
+            EncodeCodec::Lz4 => 1,
+            EncodeCodec::Snappy => 2,
+            EncodeCodec::Zlib => 3,
+            EncodeCodec::Zstd => 4,
+        }) << 5
+    }
+
+    fn encode(self, data: &[u8], level: u32) -> Result<Vec<u8>, FormatError> {
+        match self {
+            EncodeCodec::Lz4 => Ok(lz4_flex::block::compress(data)),
+            EncodeCodec::Snappy => snap::raw::Encoder::new()
+                .compress_vec(data)
+                .map_err(|e| FormatError::CompressionError(format!("blosc: snappy: {e}"))),
+            EncodeCodec::Zlib => crate::filters::deflate_bounded(data, level.min(9))
+                .map_err(|e| FormatError::CompressionError(format!("blosc: zlib: {e}"))),
+            EncodeCodec::Zstd => Ok(crate::filters_bitshuffle::zstd_encode(data)),
+        }
+    }
+}
+
+/// Block size our encoder uses: at most 256 KiB, a whole number of
+/// elements (and, for bit shuffle, of 8-element groups).
+fn encode_block_size(nbytes: usize, typesize: usize, bitshuffle: bool) -> usize {
+    let unit = if bitshuffle { 8 * typesize } else { typesize };
+    let target = (256 * 1024).min(nbytes);
+    if target < unit {
+        return nbytes.max(1);
+    }
+    target / unit * unit
+}
+
+/// Encode a chunk as one Blosc 1 frame. `cd_values` as hdf5-blosc:
+/// `[2]` type size, `[4]` level (0 = store), `[5]` shuffle, `[6]` codec.
+pub(crate) fn blosc_encode(input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    let cd = ctx.client_data();
+    let cerr = |m: &str| FormatError::CompressionError(format!("blosc: {m}"));
+    let typesize = match cd.get(2) {
+        Some(&t) if t != 0 => t as usize,
+        _ => ctx.element_size.max(1),
+    };
+    // Blosc records the type size in one byte; c-blosc treats larger types
+    // as bytes.
+    let typesize = if typesize > 255 { 1 } else { typesize };
+    let level = cd.get(4).copied().unwrap_or(5);
+    let shuffle = cd.get(5).copied().unwrap_or(1);
+    let codec = EncodeCodec::from_cd(cd.get(6).copied().unwrap_or(1))?;
+    let nbytes = input.len();
+    if nbytes > i32::MAX as usize - HEADER {
+        return Err(cerr("chunk too large for a Blosc frame"));
+    }
+    let mut flags = codec.flags();
+    match shuffle {
+        0 => {}
+        1 => flags |= FLAG_SHUFFLE,
+        2 => flags |= FLAG_BITSHUFFLE,
+        other => return Err(cerr(&format!("unknown shuffle mode {other}"))),
+    }
+    let blocksize = encode_block_size(nbytes, typesize, shuffle == 2);
+    let header = |flags: u8, blocksize: usize, cbytes: usize| {
+        let mut h = Vec::with_capacity(HEADER);
+        h.extend_from_slice(&[2, 1, flags, typesize as u8]);
+        h.extend_from_slice(&(nbytes as u32).to_le_bytes());
+        h.extend_from_slice(&(blocksize as u32).to_le_bytes());
+        h.extend_from_slice(&(cbytes as u32).to_le_bytes());
+        h
+    };
+    let stored = || {
+        let mut out = header(
+            FLAG_MEMCPYED | (flags & !(FLAG_SHUFFLE | FLAG_BITSHUFFLE)),
+            blocksize,
+            nbytes + HEADER,
+        );
+        out.extend_from_slice(input);
+        out
+    };
+    if level == 0 || nbytes == 0 {
+        return Ok(stored());
+    }
+
+    let nblocks = nbytes.div_ceil(blocksize);
+    let leftover = nbytes % blocksize;
+    let mut body = Vec::with_capacity(nbytes / 2);
+    let mut starts = Vec::with_capacity(nblocks);
+    let table_end = HEADER + 4 * nblocks;
+    let mut shuffled = vec![0u8; blocksize];
+    for j in 0..nblocks {
+        let is_leftover = j == nblocks - 1 && leftover > 0;
+        let bsize = if is_leftover { leftover } else { blocksize };
+        let block = &input[j * blocksize..j * blocksize + bsize];
+        let sh = &mut shuffled[..bsize];
+        shuffle_block(flags, typesize, block, sh);
+        starts.push(table_end + body.len());
+        let nsplits = if typesize <= MAX_SPLITS
+            && bsize / typesize >= MIN_BUFFERSIZE
+            && !is_leftover
+            && bsize.is_multiple_of(typesize)
+        {
+            typesize
+        } else {
+            1
+        };
+        let neblock = bsize / nsplits;
+        for s in 0..nsplits {
+            let part = &sh[s * neblock..(s + 1) * neblock];
+            let comp = codec.encode(part, level)?;
+            if comp.len() < neblock {
+                body.extend_from_slice(&(comp.len() as u32).to_le_bytes());
+                body.extend_from_slice(&comp);
+            } else {
+                body.extend_from_slice(&(neblock as u32).to_le_bytes());
+                body.extend_from_slice(part);
+            }
+        }
+        if table_end + body.len() >= nbytes + HEADER {
+            // Incompressible: store instead, as c-blosc does.
+            return Ok(stored());
+        }
+    }
+    // A split block must decode as split: the decoder infers splitting from
+    // the same rule, which requires a whole number of elements per block.
+    let cbytes = table_end + body.len();
+    let mut out = header(flags, blocksize, cbytes);
+    for s in starts {
+        out.extend_from_slice(&(s as u32).to_le_bytes());
+    }
+    out.extend_from_slice(&body);
+    Ok(out)
+}
+
+/// Apply the frame's shuffle to one block (the inverse of
+/// [`unshuffle_block`]).
+fn shuffle_block(flags: u8, typesize: usize, src: &[u8], dest: &mut [u8]) {
+    let bsize = src.len();
+    if flags & FLAG_SHUFFLE != 0 && typesize > 1 {
+        let n = bsize / typesize;
+        for i in 0..n {
+            for b in 0..typesize {
+                dest[b * n + i] = src[i * typesize + b];
+            }
+        }
+        dest[n * typesize..].copy_from_slice(&src[n * typesize..]);
+    } else if flags & FLAG_BITSHUFFLE != 0 && bsize >= typesize {
+        let n = bsize / typesize;
+        if n.is_multiple_of(8) {
+            let body = n * typesize;
+            bitshuffle_block(&src[..body], &mut dest[..body], n, typesize);
+            dest[body..].copy_from_slice(&src[body..]);
+        } else {
+            dest.copy_from_slice(src);
+        }
+    } else {
+        dest.copy_from_slice(src);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::filter_pipeline::{FILTER_BLOSC, FilterDescription};
+
+    /// A blosclz stream: literal "abc", then a 9-byte match 3 back (a run
+    /// of "abc"), then literal "Z".
+    #[test]
+    fn blosclz_decodes_literals_and_overlapping_matches() {
+        // Match: length (ctrl >> 5) + 2 = 8, distance ofs + code + 1 = 3.
+        let stream = [2, b'a', b'b', b'c', (6 << 5), 2, 0, b'Z'];
+        let mut out = [0u8; 12];
+        assert_eq!(blosclz_decompress(&stream, &mut out), 12);
+        assert_eq!(&out, b"abcabcabcabZ");
+        // A stream cut inside a match is malformed.
+        let mut out = [0u8; 11];
+        assert_eq!(blosclz_decompress(&stream[..6], &mut out), 0);
+        // A match before the start of the output is malformed.
+        assert_eq!(blosclz_decompress(&[0, b'a', 32, 5, 0, b'x'], &mut out), 0);
+    }
+
+    fn desc(cd: Vec<u32>) -> FilterDescription {
+        FilterDescription {
+            filter_id: FILTER_BLOSC,
+            name: None,
+            flags: 0,
+            client_data: cd,
+        }
+    }
+
+    #[test]
+    fn frame_round_trips_every_codec_and_shuffle() {
+        for ts in [1usize, 2, 4, 8, 3, 32] {
+            for n in [0usize, 5, 100, 1000, 70_000, 300_001] {
+                if n * ts > 1 << 20 && ts > 1 {
+                    continue;
+                }
+                let data: Vec<u8> = (0..n * ts)
+                    .map(|i| ((i / ts) % 200) as u8 ^ (i % ts) as u8)
+                    .collect();
+                for codec in [1u32, 3, 4, 5] {
+                    for shuffle in [0u32, 1, 2] {
+                        for level in [0u32, 5] {
+                            let f = desc(vec![2, 2, ts as u32, 0, level, shuffle, codec]);
+                            let ctx = FilterContext {
+                                filter: &f,
+                                element_size: ts,
+                                max_output: data.len(),
+                            };
+                            let enc = blosc_encode(&data, &ctx).unwrap();
+                            let dec = blosc_decode(&enc, &ctx).unwrap_or_else(|e| {
+                                panic!("ts={ts} n={n} codec={codec} shuffle={shuffle}: {e}")
+                            });
+                            assert!(
+                                dec == data,
+                                "ts={ts} n={n} codec={codec} shuffle={shuffle} level={level}"
+                            );
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn rejects_bad_frames() {
+        let data = vec![9u8; 50_000];
+        let f = desc(vec![2, 2, 4, 0, 5, 1, 1]);
+        let ctx = FilterContext {
+            filter: &f,
+            element_size: 4,
+            max_output: data.len(),
+        };
+        let enc = blosc_encode(&data, &ctx).unwrap();
+        assert!(blosc_decode(&enc[..enc.len() - 3], &ctx).is_err());
+        let small = FilterContext {
+            max_output: 49_999,
+            ..ctx
+        };
+        assert!(blosc_decode(&enc, &small).is_err());
+        let mut v3 = enc.clone();
+        v3[0] = 3;
+        assert!(blosc_decode(&v3, &ctx).is_err());
+        let f0 = desc(vec![2, 2, 4, 0, 5, 1, 0]);
+        let ctx0 = FilterContext { filter: &f0, ..ctx };
+        assert!(blosc_encode(&data, &ctx0).is_err());
+    }
+
+    /// A frame that declares no data, for a chunk that has some.
+    #[test]
+    fn empty_frame_for_a_non_empty_chunk_is_an_error() {
+        let mut frame = vec![2u8, 1, 0x20, 4];
+        for v in [0u32, 64, 16] {
+            frame.extend_from_slice(&v.to_le_bytes());
+        }
+        assert_eq!(blosc_decompress(&frame, 64).unwrap(), b"");
+        let f = desc(vec![2, 2, 4, 64, 5, 1, 1]);
+        let ctx = FilterContext {
+            filter: &f,
+            element_size: 4,
+            max_output: 64,
+        };
+        assert!(blosc_decode(&frame, &ctx).is_err());
+    }
+
+    /// A frame whose header claims a compressed size smaller than the
+    /// header itself, not stored raw: an error, not an arithmetic overflow
+    /// (it panicked in debug builds).
+    #[test]
+    fn frame_size_below_the_header_is_an_error() {
+        let mut frame = vec![2u8, 1, 1 << 5, 4];
+        for v in [64u32, 64, 8] {
+            frame.extend_from_slice(&v.to_le_bytes());
+        }
+        frame.extend_from_slice(&[0; 40]);
+        assert!(blosc_decompress(&frame, 1000).is_err());
+        for cbytes in 0..16u32 {
+            frame[12..16].copy_from_slice(&cbytes.to_le_bytes());
+            assert!(blosc_decompress(&frame, 1000).is_err(), "cbytes={cbytes}");
+        }
+    }
+
+    /// A BloscLZ frame (our encoder cannot write one): a single block,
+    /// one stream, no shuffle.
+    fn blosclz_frame() -> Vec<u8> {
+        let stream = [2, b'a', b'b', b'c', (6 << 5), 2, 0, b'Z'];
+        let mut f = vec![2u8, 1, 0, 1];
+        for v in [12u32, 12, (HEADER + 4 + 4 + stream.len()) as u32] {
+            f.extend_from_slice(&v.to_le_bytes());
+        }
+        f.extend_from_slice(&((HEADER + 4) as u32).to_le_bytes());
+        f.extend_from_slice(&(stream.len() as u32).to_le_bytes());
+        f.extend_from_slice(&stream);
+        f
+    }
+
+    /// Random and mutated frames, every codec and shuffle: errors are fine,
+    /// panics are not.
+    #[test]
+    fn fuzzed_frames_never_panic() {
+        let limit = 6000;
+        let data: Vec<u8> = (0..1500u32).flat_map(|i| (i / 5).to_le_bytes()).collect();
+        let mut seeds = vec![blosclz_frame()];
+        for codec in [1u32, 3, 4, 5] {
+            for shuffle in [0u32, 1, 2] {
+                for (ts, n) in [(4usize, data.len()), (4, 520), (1, 300), (2, 4)] {
+                    let f = desc(vec![2, 2, ts as u32, 0, 5, shuffle, codec]);
+                    let ctx = FilterContext {
+                        filter: &f,
+                        element_size: ts,
+                        max_output: n,
+                    };
+                    seeds.push(blosc_encode(&data[..n], &ctx).unwrap());
+                }
+            }
+        }
+        // Stored raw.
+        let f = desc(vec![2, 2, 4, 0, 0, 1, 1]);
+        let ctx = FilterContext {
+            filter: &f,
+            element_size: 4,
+            max_output: 64,
+        };
+        seeds.push(blosc_encode(&data[..64], &ctx).unwrap());
+        crate::test_fuzz::fuzz_decoder(0xb10, &seeds, 30_000, limit, |s| {
+            blosc_decompress(s, limit)
+        });
+    }
+
+    /// BloscLZ streams on their own, random and mutated.
+    #[test]
+    fn fuzzed_blosclz_streams_never_panic() {
+        let seed = blosclz_frame()[HEADER + 8..].to_vec();
+        let mut out = [0u8; 64];
+        crate::test_fuzz::fuzz_decoder(0xb11, &[seed], 30_000, 64, |s| {
+            let n = blosclz_decompress(s, &mut out);
+            if n == 0 {
+                Err(err("malformed"))
+            } else {
+                Ok(out[..n].to_vec())
+            }
+        });
+    }
+}

crates/clawhdf5-format/src/filters_bzip2.rs

@@ -0,0 +1,132 @@
+//! bzip2 (HDF5 filter 307, PyTables' `H5Zbzip2.c`, hdf5plugin's `BZip2`).
+//!
+//! The chunk is one bzip2 stream; `cd_values[0]` is the block size (1-9,
+//! the compression level). Decoded with the `bzip2` crate's default backend,
+//! `libbz2-rs-sys`, a pure-Rust port of libbzip2.
+
+use crate::error::FormatError;
+use crate::filter_registry::FilterContext;
+
+fn err(msg: &str) -> FormatError {
+    FormatError::DecompressionError(format!("bzip2: {msg}"))
+}
+
+/// Decode a bzip2-filtered chunk, refusing output beyond the chunk size.
+pub(crate) fn bzip2_decode(input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    use bzip2::{Decompress, Status};
+    let limit = ctx.output_limit();
+    let max_capacity = limit.saturating_add(1);
+    let hint = if ctx.max_output != 0 {
+        ctx.max_output
+    } else {
+        input.len().saturating_mul(4)
+    };
+    let mut out = Vec::new();
+    out.try_reserve_exact(hint.clamp(1, max_capacity))
+        .map_err(|_| err("cannot allocate the output buffer"))?;
+    let mut dec = Decompress::new(false);
+    loop {
+        let (in_before, out_before) = (dec.total_in(), dec.total_out());
+        let status = dec
+            .decompress_vec(&input[in_before as usize..], &mut out)
+            .map_err(|e| err(&e.to_string()))?;
+        if out.len() > limit {
+            return Err(err("output exceeds the chunk size"));
+        }
+        if status == Status::StreamEnd {
+            return Ok(out);
+        }
+        if out.len() == out.capacity() {
+            let grow = out
+                .capacity()
+                .min(max_capacity.saturating_sub(out.capacity()))
+                .max(1);
+            out.try_reserve_exact(grow)
+                .map_err(|_| err("cannot allocate the output buffer"))?;
+        } else if dec.total_in() as usize >= input.len()
+            || (dec.total_in(), dec.total_out()) == (in_before, out_before)
+        {
+            return Err(err("truncated stream"));
+        }
+    }
+}
+
+/// Encode a chunk as one bzip2 stream at block size `cd_values[0]`
+/// (default 9, as hdf5plugin).
+pub(crate) fn bzip2_encode(input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    use bzip2::{Action, Compress, Compression, Status};
+    let level = ctx.client_data().first().copied().unwrap_or(9).clamp(1, 9);
+    let cerr = |m: String| FormatError::CompressionError(format!("bzip2: {m}"));
+    let mut enc = Compress::new(Compression::new(level), 0);
+    // bzip2's worst case is about 1% + 600 bytes over the input.
+    let mut out = Vec::with_capacity(input.len() + input.len() / 100 + 600);
+    loop {
+        let consumed = enc.total_in() as usize;
+        let status = enc
+            .compress_vec(&input[consumed..], &mut out, Action::Finish)
+            .map_err(|e| cerr(e.to_string()))?;
+        if status == Status::StreamEnd {
+            return Ok(out);
+        }
+        if out.len() == out.capacity() {
+            out.reserve(out.capacity().max(4096));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::filter_pipeline::{FILTER_BZIP2, FilterDescription};
+
+    fn desc(level: u32) -> FilterDescription {
+        FilterDescription {
+            filter_id: FILTER_BZIP2,
+            name: None,
+            flags: 0,
+            client_data: vec![level],
+        }
+    }
+
+    #[test]
+    fn round_trips_and_bounds() {
+        let data: Vec<u8> = (0..100_000u32)
+            .flat_map(|i| (i % 777).to_le_bytes())
+            .collect();
+        for level in [1, 5, 9] {
+            let f = desc(level);
+            let ctx = FilterContext {
+                filter: &f,
+                element_size: 4,
+                max_output: data.len(),
+            };
+            let enc = bzip2_encode(&data, &ctx).unwrap();
+            assert!(enc.len() < data.len() / 4);
+            assert_eq!(bzip2_decode(&enc, &ctx).unwrap(), data);
+            // Truncated, and larger than the chunk: errors, not data.
+            assert!(bzip2_decode(&enc[..enc.len() / 2], &ctx).is_err());
+            let small = FilterContext {
+                max_output: data.len() - 1,
+                ..ctx
+            };
+            assert!(bzip2_decode(&enc, &small).is_err());
+        }
+    }
+
+    /// Random and mutated streams: errors are fine, panics are not.
+    #[test]
+    fn fuzzed_streams_never_panic() {
+        let f = desc(9);
+        let data: Vec<u8> = (0..4000u32).flat_map(|i| (i % 91).to_le_bytes()).collect();
+        let ctx = FilterContext {
+            filter: &f,
+            element_size: 4,
+            max_output: data.len(),
+        };
+        let seeds = vec![
+            bzip2_encode(&data, &ctx).unwrap(),
+            bzip2_encode(&data[..40], &ctx).unwrap(),
+        ];
+        crate::test_fuzz::fuzz_decoder(0xb2, &seeds, 3_000, data.len(), |s| bzip2_decode(s, &ctx));
+    }
+}

crates/clawhdf5-format/src/filters_lzf.rs

@@ -0,0 +1,260 @@
+//! LZF (HDF5 filter 32000) — h5py's built-in compression filter
+//! (`compression="lzf"`), in pure Rust.
+//!
+//! The chunk is one raw LZF stream (liblzf 3.x format, no header). The
+//! stream is a sequence of instructions, each starting with a control byte:
+//!
+//! * `000LLLLL` — a literal run: the next `L + 1` bytes (1..=32) are copied.
+//! * `LLLOOOOO [E] OOOOOOOO` — a back reference: copy `len + 2` bytes from
+//!   `distance` bytes back, where `len` is the top three bits (1..=6), or
+//!   `7 + E` when they are all ones, and `distance` is the 13-bit offset
+//!   (high five bits in the control byte, low eight in the last byte) plus 1.
+//!
+//! h5py's filter (`lzf_filter.c`) records the chunk's size in bytes in
+//! `cd_values[2]` (slots 0 and 1 hold the filter and liblzf versions) and
+//! sizes its output buffer from it.
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+#[cfg(not(feature = "std"))]
+use alloc::{format, vec, vec::Vec};
+
+use crate::error::FormatError;
+use crate::filter_registry::FilterContext;
+
+/// `H5PY_FILTER_LZF_VERSION`, written to `cd_values[0]`.
+pub const LZF_FILTER_VERSION: u32 = 4;
+/// `LZF_VERSION` (liblzf 1.5), written to `cd_values[1]`.
+pub const LZF_API_VERSION: u32 = 0x0105;
+
+const MAX_LITERAL: usize = 32;
+const MAX_OFFSET: usize = 1 << 13;
+const MAX_REF: usize = (1 << 8) + (1 << 3);
+const HASH_LOG: u32 = 14;
+
+fn err(msg: &str) -> FormatError {
+    FormatError::DecompressionError(format!("lzf: {msg}"))
+}
+
+/// Decode an LZF-filtered chunk.
+pub(crate) fn lzf_decode(input: &[u8], ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    let limit = ctx.output_limit();
+    let hint = match ctx.client_data().get(2) {
+        Some(&n) if n != 0 => n as usize,
+        _ => input.len().saturating_mul(2),
+    };
+    lzf_decompress(input, hint.min(limit), limit)
+}
+
+/// Decompress a raw LZF stream, refusing to produce more than `limit` bytes.
+pub fn lzf_decompress(
+    input: &[u8],
+    size_hint: usize,
+    limit: usize,
+) -> Result<Vec<u8>, FormatError> {
+    let mut out: Vec<u8> = Vec::new();
+    out.try_reserve(size_hint)
+        .map_err(|_| err("cannot allocate the output buffer"))?;
+    let mut ip = 0usize;
+    while ip < input.len() {
+        let ctrl = input[ip] as usize;
+        ip += 1;
+        if ctrl < 32 {
+            let run = ctrl + 1;
+            let lit = input
+                .get(ip..ip + run)
+                .ok_or_else(|| err("literal run past the end of the input"))?;
+            if out.len() + run > limit {
+                return Err(err("output exceeds the chunk size"));
+            }
+            out.extend_from_slice(lit);
+            ip += run;
+        } else {
+            let mut len = ctrl >> 5;
+            if len == 7 {
+                len += *input
+                    .get(ip)
+                    .ok_or_else(|| err("truncated back reference"))?
+                    as usize;
+                ip += 1;
+            }
+            let low = *input
+                .get(ip)
+                .ok_or_else(|| err("truncated back reference"))? as usize;
+            ip += 1;
+            let distance = ((ctrl & 0x1f) << 8) + low + 1;
+            let len = len + 2;
+            if distance > out.len() {
+                return Err(err("back reference before the start of the output"));
+            }
+            if out.len() + len > limit {
+                return Err(err("output exceeds the chunk size"));
+            }
+            let start = out.len() - distance;
+            if distance >= len {
+                out.extend_from_within(start..start + len);
+            } else {
+                // Overlapping copy: repeats the last `distance` bytes.
+                for k in 0..len {
+                    let b = out[start + k];
+                    out.push(b);
+                }
+            }
+        }
+    }
+    Ok(out)
+}
+
+/// Encode a chunk with the LZF filter.
+pub(crate) fn lzf_encode(input: &[u8], _ctx: &FilterContext<'_>) -> Result<Vec<u8>, FormatError> {
+    Ok(lzf_compress(input))
+}
+
+fn hash3(b: &[u8]) -> usize {
+    let v = (u32::from(b[0]) << 16) | (u32::from(b[1]) << 8) | u32::from(b[2]);
+    (v.wrapping_mul(2_654_435_761) >> (32 - HASH_LOG)) as usize
+}
+
+fn flush_literals(out: &mut Vec<u8>, lit: &[u8]) {
+    for run in lit.chunks(MAX_LITERAL) {
+        out.push((run.len() - 1) as u8);
+        out.extend_from_slice(run);
+    }
+}
+
+/// Compress `input` into a raw LZF stream any liblzf decoder reads.
+///
+/// Incompressible input grows by one byte per 32. (h5py's own filter gives
+/// up on such a chunk and stores it unfiltered; storing the slightly larger
+/// stream is equally readable.)
+pub fn lzf_compress(input: &[u8]) -> Vec<u8> {
+    let n = input.len();
+    let mut out = Vec::with_capacity(n + n / MAX_LITERAL + 1);
+    let mut table = vec![0u32; 1 << HASH_LOG];
+    let mut lit_start = 0usize;
+    let mut i = 0usize;
+    while i + 2 < n {
+        let h = hash3(&input[i..]);
+        let cand = table[h] as usize;
+        table[h] = (i + 1) as u32;
+        if cand != 0 {
+            let r = cand - 1;
+            let distance = i - r;
+            if distance <= MAX_OFFSET && input[r..r + 3] == input[i..i + 3] {
+                let max_len = (n - i).min(MAX_REF);
+                let mut len = 3;
+                while len < max_len && input[r + len] == input[i + len] {
+                    len += 1;
+                }
+                flush_literals(&mut out, &input[lit_start..i]);
+                let code = len - 2;
+                let off = distance - 1;
+                if code < 7 {
+                    out.push(((code << 5) | (off >> 8)) as u8);
+                } else {
+                    out.push(((7 << 5) | (off >> 8)) as u8);
+                    out.push((code - 7) as u8);
+                }
+                out.push((off & 0xff) as u8);
+                // Index the positions the match covered so later data can
+                // refer back into it.
+                let end = i + len;
+                let mut j = i + 1;
+                while j < end && j + 2 < n {
+                    table[hash3(&input[j..])] = (j + 1) as u32;
+                    j += 1;
+                }
+                i = end;
+                lit_start = i;
+                continue;
+            }
+        }
+        i += 1;
+    }
+    flush_literals(&mut out, &input[lit_start..]);
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn round_trip(data: &[u8]) {
+        let c = lzf_compress(data);
+        assert_eq!(lzf_decompress(&c, data.len(), data.len()).unwrap(), data);
+    }
+
+    #[test]
+    fn round_trips() {
+        round_trip(b"");
+        round_trip(b"a");
+        round_trip(b"abcabcabcabcabcabcabcabcabcabcabcabc");
+        round_trip(&[7u8; 10_000]);
+        let noise: Vec<u8> = (0..70_000u32)
+            .map(|i| (i.wrapping_mul(2_654_435_761) >> 13) as u8)
+            .collect();
+        round_trip(&noise);
+        let ramp: Vec<u8> = (0..100_000u32)
+            .flat_map(|i| (i % 1000).to_le_bytes())
+            .collect();
+        round_trip(&ramp);
+    }
+
+    #[test]
+    fn compresses_repetitive_data() {
+        let data = [42u8; 4096];
+        assert!(lzf_compress(&data).len() < 100);
+    }
+
+    /// The chunk h5py 3.16's bundled liblzf writes for
+    /// `b"hello hello hello hello"` (read back with `read_direct_chunk`): a
+    /// 7-byte literal, a 14-byte back reference 6 bytes back (extended
+    /// length), and a 2-byte literal.
+    #[test]
+    fn decodes_liblzf_output() {
+        let stream = b"\x06hello h\xe0\x05\x05\x01lo";
+        assert_eq!(
+            lzf_decompress(stream, 23, 23).unwrap(),
+            b"hello hello hello hello"
+        );
+    }
+
+    #[test]
+    fn rejects_corrupt_streams() {
+        // Back reference before the start.
+        assert!(lzf_decompress(&[0x20, 0x00], 10, 10).is_err());
+        // Literal run past the end.
+        assert!(lzf_decompress(&[0x05, 1, 2], 10, 10).is_err());
+        // Output over the limit.
+        let c = lzf_compress(&[1u8; 100]);
+        assert!(lzf_decompress(&c, 10, 99).is_err());
+    }
+
+    /// Random and mutated streams: errors are fine, panics are not.
+    #[test]
+    fn fuzzed_streams_never_panic() {
+        let seeds: Vec<Vec<u8>> = [
+            b"hello hello hello hello".to_vec(),
+            vec![7u8; 3000],
+            (0..2000u32).flat_map(|i| (i % 37).to_le_bytes()).collect(),
+            (0..500u32)
+                .map(|i| (i.wrapping_mul(2_654_435_761) >> 13) as u8)
+                .collect(),
+        ]
+        .iter()
+        .map(|d| lzf_compress(d))
+        .collect();
+        for limit in [0usize, 23, 4096, 8000] {
+            crate::test_fuzz::fuzz_decoder(
+                0x1f2 + limit as u64,
+                &seeds[..1],
+                5_000,
+                limit.max(23),
+                |s| lzf_decompress(s, limit, limit.max(23)),
+            );
+        }
+        crate::test_fuzz::fuzz_decoder(0x1f3, &seeds, 20_000, 8000, |s| {
+            lzf_decompress(s, 8000, 8000)
+        });
+    }
+}