research: implementation brief for perf/security/provenance pass (INT-01..19)

Read against ROADMAP.md/IMPROVEMENT_LOG.md/CLAUDE.md/CHANGELOG.md first so
nothing already-merged is re-proposed. 19 numbered INT items grouped by
crate (clawhdf5-agent provenance wiring, clawhdf5-format/io untrusted-file
parsing, clawhdf5-ann HNSW hot path, clawhdf5-py mutex poisoning), each with
file path, problem, and proposed change, plus a suggested implementation
order for the coding phase.

research/IMPLEMENTATION_BRIEF.md

@@ -0,0 +1,434 @@
+# Implementation Brief — clawhdf5 Performance/Security/Provenance Pass
+
+**Research date:** 2026-08-16
+**Scope:** `crates/` only. Read against `ROADMAP.md`, `IMPROVEMENT_LOG.md`, `CLAUDE.md`, and
+`CHANGELOG.md` first — those documents record a genuinely large amount of prior hardening
+(WAL CRC32, `chunked_read.rs`/`data_read.rs`/`local_heap.rs`/`btree_v1.rs` bounds audits,
+Android JNI bounds checks, pyo3 bump, HNSW `prune_connections` rayon parallelism, bounded
+decompression, no_std fixes, `cargo-audit`-clean dependency tree). None of that is
+re-proposed here. Every item below was independently verified by reading the current source
+(file path + line numbers cited), not inferred from docs.
+
+`cargo audit` was run against the current lockfile: **zero vulnerability advisories**, three
+"unmaintained" warnings (`custom_derive` via `mpi`→`conv`, `number_prefix` via `tokenizers`→
+`indicatif`, `paste`) — all transitive through optional deps (`mpi-io` feature, `tokenizers`),
+no upstream fix available, not actionable as a code change. Not filed as an INT item.
+
+Also checked and found clean (no INT items filed): `clawhdf5-migrate` (zero `unwrap()` outside
+`#[test]` code in `main.rs`; `sqlite_reader.rs`/`hdf5_writer.rs`/`validate.rs` are unwrap-free),
+`clawhdf5-cli`, `clawhdf5-napi` (zero `unwrap()` in `lib.rs`), `clawhdf5-accel` SIMD dispatch
+(`is_x86_feature_detected!`/runtime gating is correct — no illegal-instruction risk),
+`clawhdf5-filters` hot path (slice-based, no byte-by-byte loops of consequence), and TODO/FIXME
+grep across all crates (the only hits are test-fixture bytes literally named `b"XXXX"`, not
+real markers).
+
+---
+
+## Priority key
+- **P0** — correctness/security bug reachable from untrusted input (crafted file, external
+  caller), should block release.
+- **P1** — real functional gap or measurable perf cost on a hot path.
+- **P2** — consistency/hardening/API-quality; safe to defer.
+
+---
+
+## Group A — `clawhdf5-agent`: provenance/security is unwired (headline finding)
+
+### INT-01 — Wire `WriteAnomalyDetector` / `ProvenanceStore` into the actual write path [P0]
+**Files:** `crates/clawhdf5-agent/src/storage.rs` (save/save_batch path), `crates/clawhdf5-agent/src/provenance.rs`, `crates/clawhdf5-agent/src/anomaly.rs`, `crates/clawhdf5-agent/src/lib.rs`
+
+**Problem:** `ROADMAP.md` Track 5 ("Memory Security & Provenance") is marked 🟢 Complete, listing
+source attribution, write anomaly detection, source isolation, and integrity verification as
+done. The types exist and are unit-tested in isolation — but `grep -rn
+"WriteAnomalyDetector\|ProvenanceStore\|SourceIsolation"` across every file in
+`clawhdf5-agent` *except* `provenance.rs`/`anomaly.rs` themselves returns nothing.
+`storage.rs` (the real save/delete/replay path) never imports or calls into either module.
+Nothing in `HDF5Memory::save`/`save_batch` populates a `ProvenanceStore`, runs a rate/pattern
+check, or routes through `SourceIsolation`. In its current state this is a library the crate
+ships but never uses on itself — every memory write today has **no** rate limiting, no pattern
+detection, and no provenance recorded, contrary to what the roadmap and any consumer relying on
+it would assume.
+
+**Change:** In `storage.rs`'s save/save_batch entry point(s), construct/thread a
+`WriteAnomalyDetector` and `ProvenanceStore` (or accept them as constructor params on the
+memory-store struct so callers can configure `AnomalyConfig`), call `record_write` +
+`check_rate_anomaly`/`check_pattern_anomaly` before persisting each chunk, and call
+`ProvenanceStore::add` with the resulting `MemoryProvenance` alongside the write. Surface
+anomaly alerts through the existing error/result type rather than silently dropping them
+(decide via a config flag whether pattern/rate hits are hard-rejects or soft warnings — a hard
+reject changes public API behavior, a warning is additive). Add an integration test that writes
+a chunk containing one of the 15 suspicious patterns and asserts the alert actually fires
+through the public save path (not just the unit-level `WriteAnomalyDetector` test).
+
+---
+
+### INT-02 — `check_pattern_anomaly` is trivially bypassed substring matching [P1]
+**File:** `crates/clawhdf5-agent/src/anomaly.rs:192-211`
+
+**Problem:**
+```rust
+let lower = chunk.to_lowercase();
+for pattern in &self.config.suspicious_patterns {
+    if lower.contains(pattern.as_str()) { ... }
+}
+```
+Matching is raw case-folded substring containment against 15 fixed literals (`"ignore
+previous"`, `"system:"`, …). Trivially defeated by inserting extra whitespace/punctuation
+(`"ignore  previous"`), splitting the phrase across two separate writes (checks are per-chunk,
+not per-session-buffer), or any non-ASCII obfuscation. As a poisoning-resistance control this
+currently only stops the laziest attacks.
+
+**Change:** Normalize input before matching (collapse whitespace/strip zero-width and combining
+characters), and consider word-boundary-tolerant/regex matching instead of raw `contains`.
+Document the remaining limitation (this is a heuristic filter, not a guarantee) rather than
+implying full poisoning resistance.
+
+---
+
+### INT-03 — `session_counts` grows unbounded and is fully rescanned on every rate check [P1]
+**File:** `crates/clawhdf5-agent/src/anomaly.rs:109, 126-133, 170-181`
+
+**Problem:** `session_counts: HashMap<String, u32>` is incremented on every `record_write` and
+never pruned — unlike `window` (which has a 60s sliding-window prune). A caller that creates
+many distinct `session_id` values (fully caller-controlled strings) grows this map without
+bound for the process lifetime. `check_rate_anomaly`'s session-level loop
+(`for (session, &count) in &self.session_counts`) then scans the *entire* historical map on
+every single check call, so per-write cost grows with total lifetime session count, not
+current activity.
+
+**Change:** Bound `session_counts` with an LRU/TTL eviction policy, or track only counts within
+the same rolling window used for `window` (see INT-05, which is closely related — the
+session-level check has its own separate bug on top of this).
+
+---
+
+### INT-04 — Sliding-window prune only inspects the front of the deque [P1]
+**File:** `crates/clawhdf5-agent/src/anomaly.rs:134-139`
+
+**Problem:**
+```rust
+self.window.push_back(event);
+let cutoff = self.last_timestamp - 60.0;
+while self.window.front().is_some_and(|e| e.timestamp < cutoff) {
+    self.window.pop_front();
+}
+```
+`WriteEvent.timestamp` is caller-supplied (not sampled from a clock inside this type), so
+nothing prevents an out-of-order/backdated event from landing behind the front after a more
+recent one. Because eviction only ever looks at `front()`, a single out-of-order event
+permanently corrupts the window — old entries behind it are never pruned, so
+`check_rate_anomaly`'s window-length count over-reports forever (and can be intentionally
+inflated by a caller that varies timestamp ordering).
+
+**Change:** Prune by retaining only entries `>= cutoff` across the whole deque
+(`self.window.retain(|e| e.timestamp >= cutoff)`), or reject/clamp non-monotonic timestamps in
+`record_write` and document that `WriteEvent.timestamp` must be non-decreasing per detector
+instance.
+
+---
+
+### INT-05 — Session-level rate check uses a lifetime cumulative counter, not a rate [P1]
+**File:** `crates/clawhdf5-agent/src/anomaly.rs:170-181` (`check_rate_anomaly`)
+
+**Problem:** `max_writes_per_session` is compared against `session_counts[session]`, which is
+incremented forever and never reset (see INT-03). This measures "how old is this session," not
+"is this session currently abusive" — any long-lived legitimate session (e.g. a persistent
+agent) permanently trips the alert once past the threshold regardless of pace, while a burst of
+writes in a brand-new session under the threshold is missed even if it's the real anomaly.
+
+**Change:** Make this a rate — either measure session writes within the existing 60s rolling
+window (reuse `window`, filtered by `session_id`) or add a separate per-session rolling window,
+rather than an unbounded lifetime total.
+
+---
+
+### INT-06 — `bfs_neighbors` re-scans all relations on every queue pop [P1]
+**File:** `crates/clawhdf5-agent/src/knowledge.rs:339-378`, hot loop at 352-365
+
+**Problem:**
+```rust
+let neighbours: Vec<u64> = self.relations.iter().filter_map(|r| { ... }).collect();
+```
+runs once per node dequeued during BFS, giving `O(visited_nodes × total_relations)` total cost.
+`get_subgraph` (`knowledge.rs:387-417`) calls `bfs_neighbors` once per seed node, multiplying
+the cost again. On a graph with a non-trivial relation count this is the dominant cost of any
+graph traversal query — the kind of memory-graph read the whole crate exists to serve
+efficiently.
+
+**Change:** Build an adjacency `HashMap<u64, Vec<u64>>` once (either eagerly maintained on
+insert/delete, or lazily built and cached with invalidation on mutation) instead of
+linear-scanning `self.relations` per hop.
+
+---
+
+### INT-07 — Quadratic eviction via `Vec::contains` inside `retain` [P1]
+**File:** `crates/clawhdf5-agent/src/consolidation.rs:345-350`
+
+**Problem:**
+```rust
+let evict_ids: Vec<u64> = episodic_indices[..evict_n].iter().map(|&i| self.records[i].id).collect();
+self.records.retain(|r| !evict_ids.contains(&r.id));
+```
+`retain` invokes the closure once per record; `Vec::contains` is `O(m)`. Worst case this is
+`O(n·m)` per consolidation pass, run periodically over the full record set.
+
+**Change:** Collect `evict_ids` into a `HashSet<u64>` before the `retain` call — `O(n)` lookup
+per record instead of `O(m)`.
+
+---
+
+### INT-08 — `MediaRef.checksum` is unkeyed FNV-1a but named/documented as a checksum [P2]
+**File:** `crates/clawhdf5-agent/src/multimodal.rs:96-97, 104, 116, 127`; compare
+`crates/clawhdf5-agent/src/provenance.rs:16-19`
+
+**Problem:** `provenance.rs` already carries an explicit doc comment (and the CHANGELOG has a
+dedicated "doc-only" entry) clarifying that its FNV-1a content hash is unkeyed and detects only
+accidental corruption, not tampering. `multimodal.rs`'s `MediaRef.checksum` field uses the same
+FNV-1a hash for the same purpose but has no equivalent caveat, and the field name "checksum"
+(vs. "hash") reads as an integrity guarantee to a downstream consumer (e.g. something in
+ZeroClaw deciding whether to trust/reuse a cached media reference).
+
+**Change:** Either rename the field (e.g. `content_fingerprint`) or add the same
+non-tamper-evidence doc comment already used in `provenance.rs`, so the two unkeyed-hash usages
+in the crate are consistently documented.
+
+---
+
+## Group B — `clawhdf5-format` / `clawhdf5-io`: untrusted-file parsing gaps
+
+The 2026-08-05 hardening pass (see CHANGELOG "Security" section) already covers
+`chunked_read.rs`/`data_read.rs`/`local_heap.rs`/`btree_v1.rs` with `ensure_len`-style overflow
+guards, a B-tree recursion-depth guard, and a `fuzz_dataset_read` target. ROADMAP.md explicitly
+flags "a full manual audit of every indexing site is still open" as unfinished — the following
+are concrete gaps found in that follow-up, in files/paths the prior pass did not touch.
+
+### INT-09 — `btree_v2.rs` recursive tree-walk has no depth cap (stack-overflow DoS) [P0]
+**File:** `crates/clawhdf5-format/src/btree_v2.rs:264-403` (`collect_internal_records`), entry
+at `176-213` (`collect_btree_v2_records`)
+
+**Problem:** `BTreeV2Header.depth: u16` (defined at line 21) is parsed straight from file bytes
+with no upper bound. `collect_internal_records` recurses with `child_depth = depth - 1` (line
+299) down to 0 with no depth-remaining cap — unlike the cyclic/self-referencing-index guards
+already added elsewhere in this hardening cycle (`fractal_heap.rs`, `object_header.rs`'s
+`depth_remaining` params, `filters.rs`'s `NBIT_MAX_DEPTH`). A crafted v2 B-tree header claiming
+`depth = 65535` (paired with a matching on-disk `"BTIN"` internal-node chain, or even a node
+that points back into itself since nothing here detects cycles either) drives ~65k stack frames
+of native recursion — an abort/crash from a small crafted file. This is reachable from real
+parse paths: `group_v2.rs:82`, `shared_message.rs:368`, `attribute.rs:384` (dense group/dense
+attribute listings — a realistic file feature, not an obscure one).
+
+**Change:** Thread a `depth_remaining: u16` (or similar) cap through
+`collect_btree_v2_records`/`collect_internal_records`, capped at some sane bound (e.g. 64,
+consistent with `NBIT_MAX_DEPTH`'s style elsewhere in this codebase), returning a `FormatError`
+instead of recursing past it.
+
+---
+
+### INT-10 — `fuzz_btree_v2` never exercises the recursive traversal where INT-09 lives [P1]
+**File:** `crates/clawhdf5-format/fuzz/fuzz_targets/fuzz_btree_v2.rs` (or wherever this target
+lives under `crates/clawhdf5-format/fuzz/`)
+
+**Problem:** The existing target only calls `BTreeV2Header::parse` — it never calls
+`collect_btree_v2_records`, so the actual tree-walk (the code path with the depth-recursion bug
+in INT-09) has zero fuzz coverage today, despite the file being in scope for a target already
+named after it.
+
+**Change:** Extend `fuzz_btree_v2` to also invoke `collect_btree_v2_records` on the parsed
+header against the fuzz input, so the recursive traversal gets the same adversarial coverage the
+header parse already has. Land this alongside INT-09 so the fix is locked in by the fuzzer, not
+just a manual patch.
+
+---
+
+### INT-11 — Unchecked multiplication of file-derived sizes in fractal-heap size math [P0]
+**File:** `crates/clawhdf5-format/src/fractal_heap.rs:479-496` (`block_size_for_row`,
+`indirect_block_heap_size`)
+
+**Problem:**
+```rust
+sbs * (1u64 << (row - 1))              // line ~484
+total += self.block_size_for_row(row) * tw   // line ~493
+```
+use plain `*` on `starting_block_size`/`table_width`, both read from the FRHP header with no
+upper-bound validation. A crafted large `starting_block_size` combined with enough rows/columns
+overflows `u64`; under `overflow-checks` (on for debug/fuzz builds, and optionally enabled in
+release) this panics — a DoS abort from a malformed fractal heap, the same bug class the
+2026-08-05 pass already fixed in sibling files.
+
+**Change:** Replace with `checked_mul`/`saturating_mul` and propagate a `FormatError` on
+overflow, matching the `ensure_len`/checked-arithmetic idiom already used in
+`chunked_read.rs`/`local_heap.rs`.
+
+---
+
+### INT-12 — Unbounded allocation from an unvalidated length before any data is read [P0]
+**Files:**
+- `crates/clawhdf5-io/src/subfiling.rs:206-210` (`SubfileManager::read_at`) —
+  `Vec::with_capacity(length as usize)` where `length: u64` is caller/layout-supplied with no
+  cap tied to actual dataset or file size.
+- `crates/clawhdf5-io/src/async_read.rs:84` (`AsyncFileReader::open`) —
+  `Vec::with_capacity(len as usize)` sized directly from `file.metadata().len()`, no cap.
+
+**Problem:** Both allocate a buffer sized from an untrusted/unvalidated length *before*
+validating it against anything (declared dataset size, actual readable bytes, or a configured
+ceiling). A crafted layout-metadata value reaching `subfiling.rs`, or a crafted/sparse file
+opened via `async_read.rs`, can trigger a multi-gigabyte-to-exabyte allocation attempt and an
+OOM abort — the same "bounded allocation" concern the CHANGELOG's `MAX_DECOMPRESS_SIZE` fix
+already addressed for the decompression path, just not yet for these two read paths.
+
+**Change:** Cap the length against a known-sane bound (file size, or a configurable ceiling
+similar in spirit to `MAX_DECOMPRESS_SIZE`/`MAX_WAL_FIELD_LEN`) before calling
+`Vec::with_capacity`, or use `try_reserve` and return a clean error on failure instead of
+aborting.
+
+---
+
+### INT-13 — `symbol_table.rs` size arithmetic doesn't use the `checked_*`/`ensure_len` idiom used elsewhere [P2]
+**File:** `crates/clawhdf5-format/src/symbol_table.rs:99-107` (`SymbolTableNode::parse`)
+
+**Problem:** `let needed = entries_start + num_symbols * entry_size;` uses plain arithmetic.
+Not exploitable to overflow on 64-bit today (`num_symbols` is bounded by its `u16` source
+field), but it's inconsistent with the rest of the audited codebase and becomes a real risk if
+either operand's type widens later.
+
+**Change:** Route through `checked_mul`/`checked_add` + `ensure_len`, matching the pattern used
+throughout `chunked_read.rs`/`data_read.rs`/`local_heap.rs`/`btree_v1.rs`.
+
+---
+
+### INT-14 — Filter bit-packing decode loops have no direct fuzz coverage [P2]
+**File:** `crates/clawhdf5-format/src/filters.rs` (scale-offset unpack ~150-270, N-Bit type-tree
+walk ~396-510); fuzz target `fuzz_filter_pipeline`
+
+**Problem:** `fuzz_filter_pipeline` only fuzzes `FilterPipeline::parse` — the filter-pipeline
+*metadata* message — not the actual decode functions in `filters.rs` that unpack
+attacker-influenced compressed bytes bit-by-bit (scale-offset, N-Bit). This is the most
+bit-twiddling-heavy code in the crate and, per the CHANGELOG, has already had real bugs found
+there in the initial hardening pass (`1 << minbits` overflow, `bit_offset + precision`
+overflow); it's exactly the kind of code that benefits most from fuzzing but currently gets none
+directly.
+
+**Change:** Add a `fuzz_filter_decode` target that feeds arbitrary bytes through the
+scale-offset and N-Bit decode entry points directly (not just pipeline metadata parsing).
+
+---
+
+## Group C — `clawhdf5-ann` (HNSW): hot-path performance
+
+`prune_connections` rayon parallelism (already shipped) is out of scope. The outer
+insert/build loop is intentionally left sequential per ROADMAP's own design note — not
+re-proposed here.
+
+### INT-15 — `compute_distance` is scalar-only; `clawhdf5-accel`'s SIMD path is never used [P1]
+**Files:** `crates/clawhdf5-ann/src/hnsw.rs:47-74` (`compute_distance`);
+`crates/clawhdf5-accel/src/lib.rs:125` (`cosine_similarity`), `:173` (`l2_distance`)
+
+**Problem:** `clawhdf5-ann`'s `Cargo.toml` has no dependency on `clawhdf5-accel` at all.
+`compute_distance` is a hand-written scalar loop for both L2 and cosine, called from every
+candidate-expansion step in `greedy_closest`, `search_layer`, and `prune_connections` — i.e.
+the entire build/insert/search hot path. `clawhdf5-accel` already provides
+runtime-feature-detected, SIMD-accelerated equivalents (AVX2/AVX-512/NEON, correctly gated per
+INT survey — see clean bill of health above) that go completely unused here.
+
+**Change:** Add a `clawhdf5-accel` dependency to `clawhdf5-ann` and route `compute_distance`
+through `l2_distance`/`cosine_similarity`. This is a drop-in replacement for the scalar
+arithmetic, not a semantic change.
+
+---
+
+### INT-16 — Best-entry-point distance is discarded and immediately recomputed [P1]
+**File:** `crates/clawhdf5-ann/src/hnsw.rs` — `greedy_closest` (749-772) computes
+`best_dist` at line 756 but returns only the `usize` node id; callers
+(`build_with_metric` 251-253, `insert` 381-389, `search` 504-506) immediately recompute
+`compute_distance(query, &vectors[ep], metric)` for that same `(query, ep)` pair before calling
+`search_layer` (which itself recomputes it again at line 783).
+
+**Problem:** Every layer transition during insert/search throws away a distance value it just
+computed and recomputes the identical value at least once more. For an L-layer index this wastes
+up to L redundant distance computations per insert/search call — pure waste on what is already
+the hottest path in the crate (compounded by INT-15 if that's not yet fixed).
+
+**Change:** Change `greedy_closest`'s return type to `(usize, f32)` (node id + its distance) and
+thread that value into the next `greedy_closest`/`search_layer` call instead of recomputing.
+
+---
+
+### INT-17 — `search_layer`'s visited-set uses `HashSet<usize>` instead of a dense bitset [P1]
+**File:** `crates/clawhdf5-ann/src/hnsw.rs:799, 809-812`
+
+**Problem:** `let mut visited = HashSet::new();` with `.contains(&neighbor)`/`.insert(neighbor)`
+in the innermost per-candidate-expansion loop, run on every insert and search call. Node ids are
+dense `0..n` integers — a `Vec<bool>` (or bitset) indexed directly by id gives O(1) lookup
+without SipHash overhead, which matters when this loop dominates search cost.
+
+**Change:** Replace with `vec![false; vectors.len()]` indexed by node id (reset/reused per
+call), or a proper bitset if allocation-per-call cost matters.
+
+---
+
+### INT-18 — `compact()` clones every surviving vector twice [P1]
+**File:** `crates/clawhdf5-ann/src/hnsw.rs:463-478` (`compact`), `:305`
+(`build_with_metric`'s `vectors: vectors.to_vec()`)
+
+**Problem:** `compact()` builds an owned `Vec<Vec<f32>>` via `surviving.push(v.clone())` (line
+469), then passes `&surviving` into `build_with_metric`, whose first action clones it again via
+`.to_vec()`. For a large index this doubles the memory-copy cost of an already-`O(n)` rebuild
+operation.
+
+**Change:** Give `build_with_metric` (or a private variant) an owned-`Vec<Vec<f32>>` entry point
+so `compact` can move `surviving` in directly instead of cloning twice.
+
+---
+
+## Group D — `clawhdf5-py`: Mutex poisoning bricks write-mode objects
+
+### INT-19 — Pervasive `state.lock().unwrap()` on a shared `Mutex` reachable from Python calls [P1]
+**Files:** `crates/clawhdf5-py/src/group.rs` (6 sites, e.g. `:115, :161, :184, :200, :217`),
+`crates/clawhdf5-py/src/attrs.rs` (4 sites, e.g. `:56, :77, :92, :99`),
+`crates/clawhdf5-py/src/file.rs` (1 site, `:282`)
+
+**Problem:** `PyGroup`/`PyAttrs`/write-mode file state hold a `Mutex<...>` and every method that
+touches it does `state.lock().unwrap()`. If any single call panics while holding the lock (a
+future edge case in `extract_numpy_data`, an allocation failure, anything) the `Mutex` becomes
+permanently poisoned. Every subsequent method call on that same Python object — for the rest of
+its lifetime — then also panics via the same `.unwrap()`, instead of the object cleanly
+returning a `PyErr` and remaining usable. This turns one transient panic into a permanently
+broken object from the caller's perspective, which is a worse failure mode than a single
+raised-and-handled Python exception.
+
+**Change:** Replace `lock().unwrap()` with a helper that converts a poison error into a
+`PyResult` `PyErr` (e.g. `state.lock().map_err(|_| PyErr::new::<PyRuntimeError, _>("internal state poisoned"))?`,
+or use `parking_lot::Mutex` which doesn't have poisoning at all — likely the simpler fix given
+`clawhdf5-py` doesn't appear to rely on poisoning semantics anywhere). Apply consistently across
+all ~11 call sites.
+
+---
+
+## Group E — noted, not proposed (checked and found low-priority/out-of-scope)
+
+- **`clawhdf5-derive`'s generated `from_bytes`** (`crates/clawhdf5-derive/src/lib.rs:106-119`)
+  does `assert!(_data.len() >= _required, ...)` before any field-slicing, so it's a documented,
+  guarded panic (`# Panics` doc comment already present) rather than an unguarded OOB — and
+  `#[derive(H5Type)]` is currently used only in `crates/clawhdf5-format/tests/derive_tests.rs`,
+  not in any production code path. Making `from_bytes` return `Result` instead of asserting
+  would be a reasonable future API-ergonomics improvement for downstream users of the macro, but
+  it's not fixing a reachable bug today — left out as not worth an INT slot this pass.
+- **`cargo audit` unmaintained warnings** (`custom_derive`, `number_prefix`, `paste`) — all
+  transitive through optional features (`mpi-io`, and whatever pulls in `tokenizers`), zero
+  actual vulnerabilities, no code-level fix available in this repo. FYI only.
+
+---
+
+## Suggested implementation order for the coding phase
+
+1. **INT-01** first — it's the load-bearing gap (provenance/anomaly detection is currently
+   inert), and INT-02/03/04/05 are bug fixes *inside* the code INT-01 wires up, so fixing them
+   before or during the wiring avoids shipping newly-live bugs.
+2. **INT-09 + INT-10 together** (P0, security) and **INT-11, INT-12** (P0, security) — these are
+   independent of each other and of Group A, safe to parallelize.
+3. **INT-15/16/17/18** (Group C, HNSW perf) — independent of A/B, safe to parallelize.
+4. **INT-19** (Group D) — independent, small, safe to parallelize.
+5. **INT-06, INT-07, INT-08, INT-13, INT-14** — lower urgency, pick up as time allows.
+
+All items should land with `cargo test --workspace` (and `cargo clippy --workspace -- -D
+warnings`, per this repo's established gate) passing before being considered done.