Initial commit: ClawSync v0.1.0

8-crate pure-Rust workspace for revision-aware HDF5 sync. ## Crates - clawhdf5-onion: ClawOnion VFD — page-level versioned HDF5 storage, binary format, writer/reader, branch DAG, GC, snapshots, provenance - clawsync-core: BLAKE3, xxHash3, FastCDC (+ SIMD NEON), zstd/lz4 - clawsync-onion: IBLT sketch, Merkle tree differ, packet differ/merger, ClawSyncManifest, SyncSelector - clawsync-hdf5: dataset-level manifest, differ, patcher, wire payload reconstruction (apply_received_payloads) - clawsync-transport: TCP, QUIC (quinn 0.11/TLS 1.3), SyncPeer abstraction, length-prefixed rkyv wire protocol (21 SyncMessage variants) - clawsync-agent: OnionMemory, SyncScheduler, TcpSyncBackend, PeerCapabilities negotiation - clawsync-fs: CDC-based delta sync for any file type; FsSyncClient/Server, W=16 pipelining, atomic writes - clawsync-cli: push/pull/serve/hdf5-sync/serve-hdf5/sync/serve-fs + all local management commands; --quic on all network commands ## Key features - IBLT pre-flight: O(revision count) vs rsync's O(file size) - W=16 sliding-window push: 13–15x speedup over stop-and-wait at WAN RTT - Dataset-granular HDF5 sync: only modified datasets transferred - CDC delta for any file type: insertion-stable chunk boundaries - Full revision DAG: branch, merge, rollback, export, snapshot, GC - QUIC transport: TLS 1.3, per-message streams via quinn 0.11 ## Tests ~573 passing (default features); ~589 with --features simd-cdc ## Performance (Apple Silicon) - Reconstruct rev=100: 68 µs (target ≤ 1 ms) - BLAKE3 Rayon 1 MB: 10.3 GiB/s (target ≥ 5 GB/s) - GC 500 revisions: 20.6 µs (target ≤ 2 s) - W=16 vs W=1 at 5 ms RTT: 14.8x speedup - No-op pre-flight at 16 MB: 4 ms vs rsync 35 ms (7.8x) Co-Authored-By: Claude Sonnet 4.6 <[email protected]>
2026-04-04 18:41:22 -05:00
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+//! Golden-file test for ClawOnion v1 binary format.
+//!
+//! Asserts that a minimal `.onion` file serialises to exact byte values at
+//! every spec-defined offset.  This test exists solely to catch **silent
+//! `zerocopy` layout regressions** — if any struct field shifts by even one
+//! byte, at least one assertion below will fire.
+//!
+//! The test vector matches §13 of `CLAWONION_SPEC.md`:
+//!   - 1 revision (rev 0) on branch `main`
+//!   - 1 page at `h5_offset = 0`, 4 096 bytes, filled with `0xAB`
+//!   - No revision annotation
+//!
+//! All offsets are little-endian (LE) as per the spec.
+
+use clawhdf5_onion::format::Codec;
+use clawhdf5_onion::writer::OnionFile;
+use tempfile::NamedTempFile;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Layout constants (must match CLAWONION_SPEC.md §2 + §3)
+// ─────────────────────────────────────────────────────────────────────────────
+
+const HEADER_SIZE:       usize = 128;
+const REV_ENTRY_SIZE:    usize = 112;
+const BRANCH_ENTRY_SIZE: usize = 40;
+const PAGE_ENTRY_SIZE:   usize = 32;
+const PAGE_SIZE:         u32   = 4096;
+
+const INDEX_OFFSET:  usize = HEADER_SIZE;                          // 128
+const BRANCH_OFFSET: usize = INDEX_OFFSET + REV_ENTRY_SIZE;        // 240
+const PT_OFFSET:     usize = BRANCH_OFFSET + BRANCH_ENTRY_SIZE;    // 280
+const PD_OFFSET:     usize = PT_OFFSET + PAGE_ENTRY_SIZE;          // 312
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Helpers
+// ─────────────────────────────────────────────────────────────────────────────
+
+fn le64(v: u64) -> [u8; 8] { v.to_le_bytes() }
+fn le32(v: u32) -> [u8; 4] { v.to_le_bytes() }
+
+/// Build the expected BLAKE3 for one 4096-byte page of 0xAB at h5_offset = 0.
+///
+/// Algorithm from spec §5:
+///   hasher.update(h5_offset.to_le_bytes())
+///   hasher.update(uncompressed_page_data)
+fn expected_blake3(page_bytes: &[u8]) -> [u8; 32] {
+    let mut h = blake3::Hasher::new();
+    h.update(&0u64.to_le_bytes()); // h5_offset = 0
+    h.update(page_bytes);
+    *h.finalize().as_bytes()
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Golden test
+// ─────────────────────────────────────────────────────────────────────────────
+
+#[test]
+fn golden_minimal_onion_byte_layout() {
+    // ── Build the test vector ────────────────────────────────────────────────
+
+    let _tmp = NamedTempFile::new().unwrap();
+    let h5_path = _tmp.path().with_extension("h5");
+    let base_bytes = b"\x89HDF\r\n\x1a\n".to_vec();
+    std::fs::write(&h5_path, &base_bytes).unwrap();
+
+    let mut onion = OnionFile::create(&h5_path, PAGE_SIZE).unwrap();
+
+    // Use Codec::None so data_size == orig_size and page data is unambiguous.
+    // This also matches the §13 spec test vector which specifies codec = None.
+    onion.set_codec(Codec::None);
+
+    let page_bytes = vec![0xABu8; PAGE_SIZE as usize];
+    let mut session = onion.begin_session(None).unwrap();
+    session.record_page(0, &page_bytes);
+    onion.commit_session(session, None).unwrap();
+
+    let bytes = onion.to_bytes().unwrap();
+
+    // ── Verify total file size ───────────────────────────────────────────────
+    // Header(128) + RevisionEntry(112) + BranchEntry(40) + PageTableEntry(32)
+    // + PageData(4096) + AnnotationHeap(9)
+    let ann_heap: &[u8] = &[0x00, 0x04, 0x00, 0x00, 0x00, b'm', b'a', b'i', b'n'];
+    let expected_total = PD_OFFSET + PAGE_SIZE as usize + ann_heap.len(); // 4417
+    assert_eq!(
+        bytes.len(), expected_total,
+        "total file size mismatch (got {}, expected {expected_total})",
+        bytes.len()
+    );
+
+    // ══════════════════════════════════════════════════════════════════════════
+    // §3.1 OnionHeader — 128 bytes @ offset 0
+    // ══════════════════════════════════════════════════════════════════════════
+
+    // [0..9] magic
+    assert_eq!(&bytes[0..9], b"CLAWONION", "magic mismatch");
+
+    // [9] format_version
+    assert_eq!(bytes[9], 0x01, "format_version");
+
+    // [10..16] _pad_align — must be zero
+    assert_eq!(&bytes[10..16], &[0u8; 6], "_pad_align must be zero");
+
+    // [16..24] feature_flags = 0x07 (COMPRESSION | BRANCHING | PROVENANCE)
+    assert_eq!(&bytes[16..24], &le64(0x07), "feature_flags");
+
+    // [24..28] page_size = 4096
+    assert_eq!(&bytes[24..28], &le32(4096), "page_size");
+
+    // [28..32] _pad_ps — must be zero
+    assert_eq!(&bytes[28..32], &[0u8; 4], "_pad_ps must be zero");
+
+    // [32..40] revision_count = 1
+    assert_eq!(&bytes[32..40], &le64(1), "revision_count");
+
+    // [40..44] branch_count = 1
+    assert_eq!(&bytes[40..44], &le32(1), "branch_count");
+
+    // [44..48] _pad_bc — must be zero
+    assert_eq!(&bytes[44..48], &[0u8; 4], "_pad_bc must be zero");
+
+    // [48..56] index_offset = 128
+    assert_eq!(&bytes[48..56], &le64(128), "index_offset");
+
+    // [56..64] branch_offset = 240
+    assert_eq!(&bytes[56..64], &le64(240), "branch_offset");
+
+    // [64..72] created_at — f64, time-dependent; skip exact value check,
+    //          but assert it's non-zero (a real Unix timestamp).
+    let created_at = f64::from_le_bytes(bytes[64..72].try_into().unwrap());
+    assert!(created_at > 0.0, "created_at should be a positive Unix timestamp");
+
+    // [72..128] reserved — 56 bytes, must all be zero
+    assert_eq!(&bytes[72..128], &[0u8; 56], "reserved header bytes must be zero");
+
+    // ══════════════════════════════════════════════════════════════════════════
+    // §3.2 RevisionEntry — 112 bytes @ offset 128
+    // ══════════════════════════════════════════════════════════════════════════
+
+    let re = INDEX_OFFSET; // 128
+
+    // [re+0..re+8] revision = 0
+    assert_eq!(&bytes[re..re+8], &le64(0), "revision number");
+
+    // [re+8..re+12] branch_id = 0 (main)
+    assert_eq!(&bytes[re+8..re+12], &le32(0), "branch_id");
+
+    // [re+12..re+16] _pad_bi — must be zero
+    assert_eq!(&bytes[re+12..re+16], &[0u8; 4], "_pad_bi must be zero");
+
+    // [re+16..re+24] parent_rev = u64::MAX (root has no parent)
+    assert_eq!(&bytes[re+16..re+24], &le64(u64::MAX), "parent_rev (NO_PARENT sentinel)");
+
+    // [re+24..re+28] page_count = 1
+    assert_eq!(&bytes[re+24..re+28], &le32(1), "page_count");
+
+    // [re+28..re+32] _pad_pc — must be zero
+    assert_eq!(&bytes[re+28..re+32], &[0u8; 4], "_pad_pc must be zero");
+
+    // [re+32..re+40] page_table_off = 280 (PT_OFFSET)
+    assert_eq!(&bytes[re+32..re+40], &le64(PT_OFFSET as u64), "page_table_off");
+
+    // [re+40..re+48] timestamp — f64, time-dependent; assert positive
+    let ts = f64::from_le_bytes(bytes[re+40..re+48].try_into().unwrap());
+    assert!(ts > 0.0, "revision timestamp should be positive");
+
+    // [re+48..re+80] blake3 — verify against spec §5 algorithm
+    let computed_blake3 = expected_blake3(&page_bytes);
+    assert_eq!(&bytes[re+48..re+80], &computed_blake3, "BLAKE3 hash mismatch");
+
+    // [re+80..re+96] session_uuid — 16 bytes UUIDv7; must be non-zero
+    assert_ne!(&bytes[re+80..re+96], &[0u8; 16], "session_uuid must not be all zeros");
+
+    // [re+96..re+104] annotation_off = 0 (no annotation)
+    assert_eq!(&bytes[re+96..re+104], &le64(0), "annotation_off must be 0 (no annotation)");
+
+    // [re+104] flags = 0 (not a snapshot)
+    assert_eq!(bytes[re+104], 0x00, "revision flags");
+
+    // [re+105..re+112] _pad_flags — must be zero
+    assert_eq!(&bytes[re+105..re+112], &[0u8; 7], "_pad_flags must be zero");
+
+    // ══════════════════════════════════════════════════════════════════════════
+    // §3.3 BranchEntry — 40 bytes @ offset 240
+    // ══════════════════════════════════════════════════════════════════════════
+
+    let be = BRANCH_OFFSET; // 240
+
+    // [be+0..be+4] id = 0 (main)
+    assert_eq!(&bytes[be..be+4], &le32(0), "branch id");
+
+    // [be+4..be+8] _pad_id — must be zero
+    assert_eq!(&bytes[be+4..be+8], &[0u8; 4], "_pad_id must be zero");
+
+    // [be+8..be+16] name_off = 1 (heap-relative; first string after reserved null)
+    assert_eq!(&bytes[be+8..be+16], &le64(1), "name_off for main branch");
+
+    // [be+16..be+24] head_rev = 0 (updated after commit)
+    assert_eq!(&bytes[be+16..be+24], &le64(0), "head_rev after first commit");
+
+    // [be+24..be+32] fork_rev = u64::MAX (main is not forked)
+    assert_eq!(&bytes[be+24..be+32], &le64(u64::MAX), "fork_rev (NO_PARENT for main)");
+
+    // [be+32..be+40] created_at — f64, time-dependent; assert positive
+    let branch_ts = f64::from_le_bytes(bytes[be+32..be+40].try_into().unwrap());
+    assert!(branch_ts > 0.0, "branch created_at should be positive");
+
+    // ══════════════════════════════════════════════════════════════════════════
+    // §3.4 PageTableEntry — 32 bytes @ offset 280
+    // ══════════════════════════════════════════════════════════════════════════
+
+    let pt = PT_OFFSET; // 280
+
+    // [pt+0..pt+8] h5_offset = 0
+    assert_eq!(&bytes[pt..pt+8], &le64(0), "h5_offset");
+
+    // [pt+8..pt+16] data_offset = 312 (PD_OFFSET, absolute file position)
+    assert_eq!(&bytes[pt+8..pt+16], &le64(PD_OFFSET as u64), "data_offset (absolute)");
+
+    // [pt+16..pt+20] orig_size = 4096
+    assert_eq!(&bytes[pt+16..pt+20], &le32(4096), "orig_size");
+
+    // [pt+20..pt+24] data_size = 4096 (codec=None → no compression)
+    assert_eq!(&bytes[pt+20..pt+24], &le32(4096), "data_size (codec=None, uncompressed)");
+
+    // [pt+24] codec = 0 (None)
+    assert_eq!(bytes[pt+24], 0x00, "codec = None (0)");
+
+    // [pt+25..pt+32] _pad — must be zero
+    assert_eq!(&bytes[pt+25..pt+32], &[0u8; 7], "_pad must be zero");
+
+    // ══════════════════════════════════════════════════════════════════════════
+    // PageData — 4096 bytes @ offset 312
+    // ══════════════════════════════════════════════════════════════════════════
+
+    assert_eq!(&bytes[PD_OFFSET..PD_OFFSET + 4096], page_bytes.as_slice(),
+        "page data must equal the uncompressed original bytes");
+
+    // ══════════════════════════════════════════════════════════════════════════
+    // §3.5 AnnotationHeap — tail of file
+    // ══════════════════════════════════════════════════════════════════════════
+
+    // Last 9 bytes: [0x00 reserved] [u32 LE length=4] ["main"]
+    assert_eq!(&bytes[bytes.len()-9..], ann_heap, "annotation heap content");
+
+    // ══════════════════════════════════════════════════════════════════════════
+    // §7 Reconstruction — verify round-trip
+    // ══════════════════════════════════════════════════════════════════════════
+
+    let reconstructed = onion.reconstruct_revision(0, &base_bytes).unwrap();
+    assert_eq!(
+        &reconstructed[..PAGE_SIZE as usize],
+        page_bytes.as_slice(),
+        "reconstruct_revision must reproduce the original page"
+    );
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Byte-exact format freeze — §13 canonical test vector
+// ─────────────────────────────────────────────────────────────────────────────
+//
+// This test builds the COMPLETE expected byte buffer from pure spec knowledge,
+// then compares it against the actual serialised output byte-for-byte.
+//
+// Dynamic fields (wall-clock timestamps, UUIDs) are zeroed in BOTH buffers
+// before the comparison — this preserves the freeze property for all layout
+// fields while remaining deterministic.
+//
+// This complements `golden_minimal_onion_byte_layout` (which checks individual
+// fields) by catching any bytes in between that neither test checks explicitly.
+
+#[test]
+fn byte_exact_format_freeze() {
+    let re = INDEX_OFFSET;  // 128 — RevisionEntry start
+    let be = BRANCH_OFFSET; // 240 — BranchEntry start
+    let pt = PT_OFFSET;     // 280 — PageTableEntry start
+    let pd = PD_OFFSET;     // 312 — PageData start
+
+    // ── Build the actual serialised file ────────────────────────────────────
+
+    let _tmp = NamedTempFile::new().unwrap();
+    let h5_path = _tmp.path().with_extension("h5");
+    std::fs::write(&h5_path, b"\x89HDF\r\n\x1a\n").unwrap();
+
+    let mut onion = OnionFile::create(&h5_path, PAGE_SIZE).unwrap();
+    onion.set_codec(Codec::None);
+
+    let page_bytes = vec![0xABu8; PAGE_SIZE as usize];
+    let mut session = onion.begin_session(None).unwrap();
+    session.record_page(0, &page_bytes);
+    onion.commit_session(session, None).unwrap();
+
+    let mut actual = onion.to_bytes().unwrap();
+
+    // ── Build the expected buffer from spec ──────────────────────────────────
+
+    let ann_heap: &[u8] = &[0x00, 0x04, 0x00, 0x00, 0x00, b'm', b'a', b'i', b'n'];
+    let total = pd + PAGE_SIZE as usize + ann_heap.len(); // 4417
+    let mut expected = vec![0u8; total];
+
+    // §3.1 OnionHeader (128 bytes)
+    expected[0..9].copy_from_slice(b"CLAWONION");  // magic
+    expected[9]   = 0x01;                          // format_version
+    // [10..16]  = 0 (_pad_align)
+    expected[16..24].copy_from_slice(&le64(0x07)); // feature_flags
+    expected[24..28].copy_from_slice(&le32(4096)); // page_size
+    // [28..32]  = 0 (_pad_ps)
+    expected[32..40].copy_from_slice(&le64(1));    // revision_count = 1
+    expected[40..44].copy_from_slice(&le32(1));    // branch_count = 1
+    // [44..48]  = 0 (_pad_bc)
+    expected[48..56].copy_from_slice(&le64(128));  // index_offset
+    expected[56..64].copy_from_slice(&le64(240));  // branch_offset
+    // [64..72]  = 0 (created_at — zeroed, dynamic)
+    // [72..128] = 0 (reserved)
+
+    // §3.2 RevisionEntry (112 bytes @ 128)
+    expected[re..re+8]  .copy_from_slice(&le64(0));        // revision = 0
+    expected[re+8..re+12].copy_from_slice(&le32(0));       // branch_id = 0
+    // [re+12..re+16] = 0 (_pad_bi)
+    expected[re+16..re+24].copy_from_slice(&le64(u64::MAX)); // parent_rev = NO_PARENT
+    expected[re+24..re+28].copy_from_slice(&le32(1));      // page_count = 1
+    // [re+28..re+32] = 0 (_pad_pc)
+    expected[re+32..re+40].copy_from_slice(&le64(pt as u64)); // page_table_off
+    // [re+40..re+48] = 0 (timestamp — zeroed, dynamic)
+    expected[re+48..re+80].copy_from_slice(&expected_blake3(&page_bytes)); // blake3
+    // [re+80..re+96] = 0 (session_uuid — zeroed, dynamic)
+    // [re+96..re+104] = 0 (annotation_off = 0, no annotation)
+    // [re+104] = 0 (flags = 0, not a snapshot)
+    // [re+105..re+112] = 0 (_pad_flags)
+
+    // §3.3 BranchEntry (40 bytes @ 240)
+    expected[be..be+4]  .copy_from_slice(&le32(0));        // id = 0 (main)
+    // [be+4..be+8] = 0 (_pad_id)
+    expected[be+8..be+16].copy_from_slice(&le64(1));       // name_off = 1 (heap offset of "main")
+    expected[be+16..be+24].copy_from_slice(&le64(0));      // head_rev = 0
+    expected[be+24..be+32].copy_from_slice(&le64(u64::MAX)); // fork_rev = NO_PARENT
+    // [be+32..be+40] = 0 (created_at — zeroed, dynamic)
+
+    // §3.4 PageTableEntry (32 bytes @ 280)
+    expected[pt..pt+8]  .copy_from_slice(&le64(0));        // h5_offset = 0
+    expected[pt+8..pt+16].copy_from_slice(&le64(pd as u64)); // data_offset
+    expected[pt+16..pt+20].copy_from_slice(&le32(4096));   // orig_size
+    expected[pt+20..pt+24].copy_from_slice(&le32(4096));   // data_size (no compression)
+    // [pt+24] = 0 (codec = None)
+    // [pt+25..pt+32] = 0 (_pad)
+
+    // PageData (4096 bytes @ 312)
+    expected[pd..pd+4096].fill(0xAB);
+
+    // §3.5 AnnotationHeap (9 bytes at end)
+    expected[pd+4096..].copy_from_slice(ann_heap);
+
+    // ── Zero dynamic fields in both buffers ──────────────────────────────────
+    // OnionHeader.created_at
+    actual[64..72].fill(0);
+    // RevisionEntry.timestamp
+    actual[re+40..re+48].fill(0);
+    // RevisionEntry.session_uuid
+    actual[re+80..re+96].fill(0);
+    // BranchEntry.created_at
+    actual[be+32..be+40].fill(0);
+
+    // ── Compare byte-for-byte ────────────────────────────────────────────────
+    assert_eq!(actual.len(), expected.len(),
+        "total file size mismatch: actual={} expected={}",
+        actual.len(), expected.len());
+
+    // Find the first differing byte for a useful failure message.
+    if actual != expected {
+        for i in 0..actual.len() {
+            if actual[i] != expected[i] {
+                panic!(
+                    "byte mismatch at offset 0x{i:03X} ({i}): \
+                     actual=0x{:02X} expected=0x{:02X}\n\
+                     (fields: header=0..128, rev_entry=128..240, branch=240..280, \
+                     page_table=280..312, page_data=312..4408, ann_heap=4408..4417)",
+                    actual[i], expected[i]
+                );
+            }
+        }
+    }
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Struct size guards — compile-time; here as runtime assertions too so that
+// a zerocopy version bump that somehow bypasses the const asserts still fires.
+// ─────────────────────────────────────────────────────────────────────────────
+
+#[test]
+fn struct_sizes_match_spec() {
+    use std::mem::size_of;
+    use clawhdf5_onion::format::{OnionHeader, RevisionEntry, BranchEntry, PageTableEntry};
+
+    assert_eq!(size_of::<OnionHeader>(),    128, "OnionHeader must be 128 bytes (§3.1)");
+    assert_eq!(size_of::<RevisionEntry>(),  112, "RevisionEntry must be 112 bytes (§3.2)");
+    assert_eq!(size_of::<BranchEntry>(),     40, "BranchEntry must be 40 bytes (§3.3)");
+    assert_eq!(size_of::<PageTableEntry>(),  32, "PageTableEntry must be 32 bytes (§3.4)");
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Magic / version rejection — §10 conformance
+// ─────────────────────────────────────────────────────────────────────────────
+
+#[test]
+fn bad_magic_is_rejected() {
+    let _tmp = NamedTempFile::new().unwrap();
+    let h5_path = _tmp.path().with_extension("h5");
+    std::fs::write(&h5_path, b"\x89HDF\r\n\x1a\n").unwrap();
+
+    let mut onion = OnionFile::create(&h5_path, 4096).unwrap();
+    onion.set_codec(Codec::None);
+    let mut s = onion.begin_session(None).unwrap();
+    s.record_page(0, &vec![0u8; 4096]);
+    onion.commit_session(s, None).unwrap();
+
+    let mut bytes = onion.to_bytes().unwrap();
+
+    // Corrupt the magic
+    bytes[0] = b'X';
+
+    let sidecar = h5_path.with_extension("h5.onion");
+    std::fs::write(&sidecar, &bytes).unwrap();
+
+    let err = OnionFile::open(&h5_path).unwrap_err();
+    assert!(
+        matches!(err, clawhdf5_onion::error::OnionError::InvalidMagic),
+        "expected InvalidMagic, got {err:?}"
+    );
+}
+
+#[test]
+fn unknown_version_is_rejected() {
+    let _tmp = NamedTempFile::new().unwrap();
+    let h5_path = _tmp.path().with_extension("h5");
+    std::fs::write(&h5_path, b"\x89HDF\r\n\x1a\n").unwrap();
+
+    let mut onion = OnionFile::create(&h5_path, 4096).unwrap();
+    onion.set_codec(Codec::None);
+    let mut s = onion.begin_session(None).unwrap();
+    s.record_page(0, &vec![0u8; 4096]);
+    onion.commit_session(s, None).unwrap();
+
+    let mut bytes = onion.to_bytes().unwrap();
+
+    // Bump format_version to something unknown
+    bytes[9] = 0xFF;
+
+    let sidecar = h5_path.with_extension("h5.onion");
+    std::fs::write(&sidecar, &bytes).unwrap();
+
+    let err = OnionFile::open(&h5_path).unwrap_err();
+    assert!(
+        matches!(err, clawhdf5_onion::error::OnionError::UnknownVersion(0xFF)),
+        "expected UnknownVersion(0xFF), got {err:?}"
+    );
+}
@@ -0,0 +1,8 @@
+# Seeds for failure cases proptest has generated in the past. It is
+# automatically read and these particular cases re-run before any
+# novel cases are generated.
+#
+# It is recommended to check this file in to source control so that
+# everyone who runs the test benefits from these saved cases.
+cc cc7ca5089f0e2c2c7c49ebf02df844567d33c457fca22d2faf0b6333d2b3d443 # shrinks to n_revisions = 7, keep_n = 1
+cc e9399e4043dbd1fb1b69988cd09e3b5746da4dc0f699d9dca701192e8a594dfd # shrinks to writes = [(0, 0), (0, 0), (0, 0), (0, 0), (0, 0)], keep_n = 1
@@ -0,0 +1,815 @@
+//! Property-based tests for `clawhdf5-onion`.
+//!
+//! These tests use `proptest` to verify invariants over arbitrary sequences of
+//! write, branch, merge, GC, and read operations, ensuring the onion format
+//! stays consistent regardless of the operation order.
+//!
+//! Invariants checked:
+//! - `head_rev` is always valid (< revision_count)
+//! - No orphan page entries (every revision index entry has accessible pages)
+//! - BLAKE3 hashes are consistent after any sequence of writes
+//! - Branch count equals unique branch IDs in revision index
+//! - GC followed by any read produces no error
+//! - Serialise → deserialise round-trip preserves all revision annotations
+//! - Merge produces a new revision on the target branch
+//! - `revision_count` is monotonically non-decreasing
+
+use clawhdf5_onion::branch::MergeStrategy;
+use clawhdf5_onion::format::NO_PARENT;
+use clawhdf5_onion::gc::GcPolicy;
+use clawhdf5_onion::writer::OnionFile;
+use proptest::prelude::*;
+use std::path::PathBuf;
+use tempfile::NamedTempFile;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Generators
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// An operation to apply to an OnionFile during a property test.
+#[derive(Debug, Clone)]
+enum Op {
+    /// Write a page at a given offset with a given fill byte.
+    Write { page_offset: u32, fill: u8 },
+    /// Fork a new branch named "branch-N" off main.
+    Fork,
+    /// Commit the current session and start fresh.
+    Flush,
+}
+
+fn arb_op() -> impl Strategy<Value = Op> {
+    prop_oneof![
+        (0u32..4u32, any::<u8>()).prop_map(|(off, fill)| Op::Write {
+            page_offset: off,
+            fill,
+        }),
+        Just(Op::Fork),
+        Just(Op::Flush),
+    ]
+}
+
+fn arb_ops(min: usize, max: usize) -> impl Strategy<Value = Vec<Op>> {
+    proptest::collection::vec(arb_op(), min..=max)
+}
+
+fn arb_page_size() -> impl Strategy<Value = u32> {
+    prop_oneof![Just(512u32), Just(1024), Just(4096)]
+}
+
+/// Create a fresh OnionFile in a temp directory.
+fn fresh_onion(page_size: u32) -> (NamedTempFile, PathBuf, OnionFile) {
+    let f = NamedTempFile::new().unwrap();
+    let h5 = f.path().with_extension("h5");
+    std::fs::write(&h5, b"\x89HDF\r\n\x1a\n").unwrap();
+    let onion = OnionFile::create(&h5, page_size).unwrap();
+    (f, h5, onion)
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Helpers
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// Apply a list of ops to an OnionFile.  Returns the number of revisions committed.
+fn apply_ops(onion: &mut OnionFile, ops: &[Op]) -> u64 {
+    let mut session = onion.begin_session(None).unwrap();
+    let page_size = onion.page_size() as usize;
+    let mut fork_count = 0usize;
+    let mut has_writes = false;
+
+    for op in ops {
+        match op {
+            Op::Write { page_offset, fill } => {
+                let offset = (*page_offset as u64) * (page_size as u64);
+                session.record_page(offset, &vec![*fill; page_size]);
+                has_writes = true;
+            }
+            Op::Fork => {
+                // Commit current session first
+                if has_writes {
+                    onion.commit_session(session, Some("auto")).unwrap();
+                    has_writes = false;
+                } else {
+                    drop(session);
+                }
+                // Fork a new branch
+                let branch_name = format!("branch-{fork_count}");
+                fork_count += 1;
+                let _ = onion.create_branch(&branch_name, "main");
+                // Restart session on main
+                session = onion.begin_session(None).unwrap();
+            }
+            Op::Flush => {
+                if has_writes {
+                    onion.commit_session(session, Some("flush")).unwrap();
+                    has_writes = false;
+                } else {
+                    drop(session);
+                }
+                session = onion.begin_session(None).unwrap();
+            }
+        }
+    }
+
+    // Commit trailing session if it has writes
+    if has_writes {
+        onion.commit_session(session, Some("final")).unwrap();
+    } else {
+        drop(session);
+    }
+
+    onion.revision_count()
+}
+
+/// Check all invariants on an OnionFile.
+fn assert_invariants(onion: &OnionFile) {
+    let revisions = onion.list_revisions();
+    let rev_count = onion.revision_count();
+
+    // 1. revision_count matches actual revision list length
+    assert_eq!(
+        rev_count as usize,
+        revisions.len(),
+        "revision_count mismatch: header={rev_count} list={}",
+        revisions.len()
+    );
+
+    // 2. Revision numbers are monotonically increasing from 0
+    for (i, rev) in revisions.iter().enumerate() {
+        assert_eq!(
+            rev.revision, i as u64,
+            "non-contiguous revision at index {i}: revision={}",
+            rev.revision
+        );
+    }
+
+    // 3. parent_rev is either NO_PARENT or a valid earlier revision
+    for rev in &revisions {
+        if rev.parent_rev != NO_PARENT {
+            assert!(
+                rev.parent_rev < rev.revision,
+                "revision {} has parent {} ≥ itself",
+                rev.revision,
+                rev.parent_rev
+            );
+        }
+    }
+
+    // 4. branch_id references are all valid
+    let branch_ids: std::collections::HashSet<u32> =
+        onion.list_branches().iter().map(|b| b.id).collect();
+    for rev in &revisions {
+        assert!(
+            branch_ids.contains(&rev.branch_id),
+            "revision {} references unknown branch_id {}",
+            rev.revision,
+            rev.branch_id
+        );
+    }
+
+    // 5. blake3_hex has correct length (64 chars)
+    for rev in &revisions {
+        assert_eq!(
+            rev.blake3_hex.len(),
+            64,
+            "revision {} has blake3_hex of wrong length {}",
+            rev.revision,
+            rev.blake3_hex.len()
+        );
+        assert!(
+            rev.blake3_hex.chars().all(|c| c.is_ascii_hexdigit()),
+            "revision {} has non-hex blake3_hex: {}",
+            rev.revision,
+            &rev.blake3_hex
+        );
+    }
+
+    // 6. Pages are accessible for every revision
+    for rev in &revisions {
+        onion
+            .revision_pages(rev.revision)
+            .unwrap_or_else(|e| panic!("revision_pages({}) failed: {e}", rev.revision));
+    }
+
+    // 7. branch head revisions are valid
+    for branch in onion.list_branches() {
+        if branch.head_rev != NO_PARENT {
+            assert!(
+                branch.head_rev < rev_count,
+                "branch {} head_rev {} >= revision_count {}",
+                branch.name,
+                branch.head_rev,
+                rev_count
+            );
+        }
+    }
+}
+
+/// Check GC-safe invariants — like `assert_invariants` but allows non-contiguous
+/// revision numbering (GC keeps original IDs) and gaps in the parent chain.
+fn assert_gc_invariants(onion: &OnionFile) {
+    let revisions = onion.list_revisions();
+    let rev_count = onion.revision_count();
+
+    // 1. revision_count matches actual revision list length
+    assert_eq!(
+        rev_count as usize,
+        revisions.len(),
+        "revision_count mismatch: header={rev_count} list={}",
+        revisions.len()
+    );
+
+    // 2. Revision numbers are monotonically increasing (gaps allowed after GC)
+    for w in revisions.windows(2) {
+        assert!(
+            w[0].revision < w[1].revision,
+            "revisions not sorted: {} then {}",
+            w[0].revision,
+            w[1].revision
+        );
+    }
+
+    // 3. parent_rev is either NO_PARENT or a valid earlier revision number
+    let rev_set: std::collections::HashSet<u64> = revisions.iter().map(|r| r.revision).collect();
+    for rev in &revisions {
+        if rev.parent_rev != NO_PARENT {
+            assert!(
+                rev.parent_rev < rev.revision,
+                "revision {} has parent {} ≥ itself",
+                rev.revision,
+                rev.parent_rev
+            );
+            // After GC the parent may have been pruned (oldest_surviving is set to NO_PARENT
+            // during consolidation), so we only check that parent < self (not that it exists).
+            let _ = &rev_set; // suppress unused warning
+        }
+    }
+
+    // 4. branch_id references are all valid
+    let branch_ids: std::collections::HashSet<u32> =
+        onion.list_branches().iter().map(|b| b.id).collect();
+    for rev in &revisions {
+        assert!(
+            branch_ids.contains(&rev.branch_id),
+            "revision {} references unknown branch_id {}",
+            rev.revision,
+            rev.branch_id
+        );
+    }
+
+    // 5. blake3_hex has correct length (64 chars)
+    for rev in &revisions {
+        assert_eq!(rev.blake3_hex.len(), 64,
+            "revision {} has blake3_hex of wrong length {}", rev.revision, rev.blake3_hex.len());
+    }
+
+    // 6. Pages are accessible for every revision
+    for rev in &revisions {
+        onion
+            .revision_pages(rev.revision)
+            .unwrap_or_else(|e| panic!("revision_pages({}) failed: {e}", rev.revision));
+    }
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Property tests
+// ─────────────────────────────────────────────────────────────────────────────
+
+proptest! {
+    #![proptest_config(ProptestConfig {
+        cases: 300,
+        max_shrink_iters: 100,
+        ..ProptestConfig::default()
+    })]
+
+    /// Any sequence of write ops leaves the onion in a valid state.
+    #[test]
+    fn prop_any_write_sequence_is_consistent(
+        page_size in arb_page_size(),
+        ops in arb_ops(1, 20),
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(page_size);
+        apply_ops(&mut onion, &ops);
+        assert_invariants(&onion);
+    }
+
+    /// revision_count never decreases.
+    #[test]
+    fn prop_revision_count_monotone(ops in arb_ops(1, 15)) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        let mut prev = 0u64;
+        // Apply ops in batches of 3, checking after each batch
+        for chunk in ops.chunks(3) {
+            apply_ops(&mut onion, chunk);
+            let cur = onion.revision_count();
+            prop_assert!(cur >= prev, "revision_count decreased: {prev} → {cur}");
+            prev = cur;
+        }
+    }
+
+    /// Every revision annotation stored is retrievable.
+    #[test]
+    fn prop_annotations_roundtrip(
+        annotations in proptest::collection::vec(
+            proptest::option::of("[a-zA-Z0-9 _-]{0,40}"),
+            1..=10usize,
+        )
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        for (i, ann) in annotations.iter().enumerate() {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; 4096]);
+            onion.commit_session(s, ann.as_deref()).unwrap();
+        }
+        let revisions = onion.list_revisions();
+        for (rev_entry, expected_ann) in revisions.iter().zip(annotations.iter()) {
+            prop_assert_eq!(
+                &rev_entry.annotation,
+                expected_ann,
+                "annotation mismatch at revision {}",
+                rev_entry.revision
+            );
+        }
+    }
+
+    /// Creating any number of branches in [0, 8] leaves list_branches consistent.
+    #[test]
+    fn prop_branch_count_consistent(n_branches in 0usize..=8usize) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        // Write one revision to main so fork has a valid HEAD
+        let mut s = onion.begin_session(None).unwrap();
+        s.record_page(0, &vec![0xAAu8; 4096]);
+        onion.commit_session(s, None).unwrap();
+
+        let mut created = 0;
+        for i in 0..n_branches {
+            let name = format!("branch-{i}");
+            if onion.create_branch(&name, "main").is_ok() {
+                created += 1;
+            }
+        }
+
+        let branches = onion.list_branches();
+        // +1 for main
+        prop_assert_eq!(branches.len(), created + 1,
+            "expected {} branches (including main), got {}", created + 1, branches.len());
+    }
+
+    /// Page data for the most recent revision of main always matches the last written fill byte.
+    #[test]
+    fn prop_latest_page_reflects_last_write(
+        fills in proptest::collection::vec(any::<u8>(), 1..=10usize),
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        for &fill in &fills {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![fill; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        let head_rev = onion.revision_count() - 1;
+        let pages = onion.revision_pages(head_rev).unwrap();
+        let page_data = &pages[0].1;
+        let expected_fill = *fills.last().unwrap();
+        prop_assert!(
+            page_data.iter().all(|&b| b == expected_fill),
+            "head page fill mismatch: expected 0x{:02x}, got first byte 0x{:02x}",
+            expected_fill, page_data[0]
+        );
+    }
+
+    /// BLAKE3 hex for every revision is unique (no two revisions with identical page content
+    /// sharing a hash — all revisions have distinct page contents due to unique fill bytes).
+    ///
+    /// We write n revisions each with a distinct fill byte, then verify all blake3s differ.
+    #[test]
+    fn prop_distinct_writes_have_distinct_hashes(
+        fills in proptest::collection::vec(0u8..=127u8, 2..=8usize).prop_filter(
+            "fills must be unique",
+            |v| {
+                let s: std::collections::HashSet<u8> = v.iter().copied().collect();
+                s.len() == v.len()
+            }
+        )
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        for &fill in &fills {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![fill; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        let hashes: Vec<_> = onion.list_revisions().into_iter().map(|r| r.blake3_hex).collect();
+        let unique: std::collections::HashSet<_> = hashes.iter().collect();
+        prop_assert_eq!(unique.len(), hashes.len(), "duplicate blake3 hashes found");
+    }
+
+    /// Serialize → deserialize round-trip: all revision annotations survive.
+    #[test]
+    fn prop_serde_roundtrip_preserves_annotations(
+        n_revisions in 1usize..=10usize,
+        ann_len in 0usize..=30usize,
+    ) {
+        let (_f, h5_path, mut onion) = fresh_onion(4096);
+        for i in 0..n_revisions {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8 % 255; 4096]);
+            let ann: String = format!("rev-{i:0>width$}", width = ann_len.min(20));
+            onion.commit_session(s, Some(&ann)).unwrap();
+        }
+        onion.flush().unwrap();
+
+        // Reload from disk
+        let reloaded = OnionFile::open(&h5_path).unwrap();
+        let orig_revs = onion.list_revisions();
+        let reloaded_revs = reloaded.list_revisions();
+
+        prop_assert_eq!(orig_revs.len(), reloaded_revs.len());
+        for (o, r) in orig_revs.iter().zip(reloaded_revs.iter()) {
+            prop_assert_eq!(&o.annotation, &r.annotation,
+                "annotation mismatch at revision {}", o.revision);
+            prop_assert_eq!(&o.blake3_hex, &r.blake3_hex,
+                "blake3 mismatch at revision {}", o.revision);
+        }
+    }
+
+    /// After any fork, the new branch starts with the same HEAD as main.
+    #[test]
+    fn prop_fork_head_equals_source_head(n_writes in 1usize..=5usize) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        for i in 0..n_writes {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        let main_head_before = onion.list_branches()
+            .iter().find(|b| b.name == "main").unwrap().head_rev;
+
+        onion.create_branch("feat", "main").unwrap();
+
+        let feat_branch = onion.list_branches()
+            .into_iter().find(|b| b.name == "feat").unwrap();
+
+        prop_assert_eq!(
+            feat_branch.fork_rev, main_head_before,
+            "fork_rev should equal main HEAD at fork time"
+        );
+    }
+
+    /// Merging branch into main with LatestWins always produces at least one new revision.
+    #[test]
+    fn prop_merge_latest_wins_produces_new_revision(
+        n_main in 1usize..=4usize,
+        n_feat in 1usize..=4usize,
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        for i in 0..n_main {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+        onion.create_branch("feat", "main").unwrap();
+        let feat_id = onion.branch_by_name("feat").unwrap().id;
+
+        for i in 0..n_feat {
+            let mut s = onion.begin_session(Some(feat_id)).unwrap();
+            s.record_page(0, &vec![0x80 + i as u8; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        let rev_before = onion.revision_count();
+        onion.merge_into("feat", "main", MergeStrategy::LatestWins).unwrap();
+        let rev_after = onion.revision_count();
+
+        prop_assert!(rev_after > rev_before, "merge did not produce a new revision");
+        assert_invariants(&onion);
+    }
+
+    /// Multiple sequential merges stay consistent.
+    #[test]
+    fn prop_sequential_merges_consistent(n_rounds in 1usize..=3usize) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        // One main revision
+        let mut s = onion.begin_session(None).unwrap();
+        s.record_page(0, &vec![0u8; 4096]);
+        onion.commit_session(s, None).unwrap();
+
+        for round in 0..n_rounds {
+            let branch_name = format!("feat-{round}");
+            onion.create_branch(&branch_name, "main").unwrap();
+            let bid = onion.branch_by_name(&branch_name).unwrap().id;
+
+            let mut s = onion.begin_session(Some(bid)).unwrap();
+            s.record_page(0, &vec![round as u8 + 1; 4096]);
+            onion.commit_session(s, None).unwrap();
+
+            onion.merge_into(&branch_name, "main", MergeStrategy::LatestWins).unwrap();
+            assert_invariants(&onion);
+        }
+    }
+
+    /// Empty sessions (no pages recorded) can be committed without breaking state.
+    #[test]
+    fn prop_empty_sessions_do_not_corrupt(n_empty in 1usize..=5usize) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        // One real write to anchor things
+        let mut s = onion.begin_session(None).unwrap();
+        s.record_page(0, &vec![0xAAu8; 4096]);
+        onion.commit_session(s, Some("anchor")).unwrap();
+
+        for _ in 0..n_empty {
+            let s = onion.begin_session(None).unwrap();
+            onion.commit_session(s, None).unwrap();
+        }
+
+        assert_invariants(&onion);
+    }
+
+    /// revision_pages never returns data of the wrong size.
+    #[test]
+    fn prop_revision_pages_correct_size(
+        n_revisions in 1usize..=8usize,
+        page_size in arb_page_size(),
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(page_size);
+        for i in 0..n_revisions {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; page_size as usize]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        for rev in 0..n_revisions as u64 {
+            let pages = onion.revision_pages(rev).unwrap();
+            for (_, data) in &pages {
+                prop_assert_eq!(
+                    data.len(), page_size as usize,
+                    "page data len {} != page_size {} at rev {}", data.len(), page_size, rev
+                );
+            }
+        }
+    }
+
+    /// After a rename, the branch is accessible under the new name only.
+    #[test]
+    fn prop_rename_branch_accessible_by_new_name(
+        old_suffix in "[a-z]{3,6}",
+        new_suffix in "[a-z]{3,6}",
+    ) {
+        prop_assume!(old_suffix != new_suffix);
+
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        let mut s = onion.begin_session(None).unwrap();
+        s.record_page(0, &vec![1u8; 4096]);
+        onion.commit_session(s, None).unwrap();
+
+        let old_name = format!("branch-{old_suffix}");
+        let new_name = format!("branch-{new_suffix}");
+
+        onion.create_branch(&old_name, "main").unwrap();
+        onion.rename_branch(&old_name, &new_name).unwrap();
+
+        prop_assert!(onion.branch_by_name(&old_name).is_none(),
+            "old name still accessible after rename");
+        prop_assert!(onion.branch_by_name(&new_name).is_some(),
+            "new name not accessible after rename");
+    }
+
+    /// GC `KeepLastN` — surviving revisions reconstruct to the same page data as before GC.
+    #[test]
+    fn prop_gc_keep_last_n_surviving_pages_unchanged(
+        // Write between 2 and 12 revisions, each writing distinct fill bytes at
+        // one of 4 page offsets.
+        writes in proptest::collection::vec(
+            (0u32..4u32, any::<u8>()),
+            2..=12usize,
+        ),
+        // Keep between 1 and all revisions.
+        keep_n in 1u64..=12u64,
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+
+        for (page_off, fill) in &writes {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page((*page_off as u64) * 4096, &vec![*fill; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        let rev_count = onion.revision_count();
+        let keep_n = keep_n.min(rev_count);
+
+        // Capture page data for all revisions before GC.
+        let before: Vec<Vec<(u64, Vec<u8>)>> = (0..rev_count)
+            .map(|rev| onion.revision_pages(rev).unwrap())
+            .collect();
+
+        // Run GC.
+        let stats = onion.gc(GcPolicy::KeepLastN(keep_n)).unwrap();
+
+        // The number of surviving revisions should equal min(keep_n, rev_count).
+        let surviving = onion.revision_count();
+        prop_assert_eq!(surviving, keep_n.min(rev_count),
+            "after KeepLastN({}), expected {}, got {} revisions",
+            keep_n, keep_n.min(rev_count), surviving);
+
+        // GC removed rev_count - surviving revisions.
+        prop_assert_eq!(stats.revisions_removed, rev_count - surviving,
+            "revisions_removed mismatch");
+
+        // Surviving revisions satisfy GC-safe invariants (non-contiguous IDs allowed).
+        assert_gc_invariants(&onion);
+
+        // For every surviving revision, `revision_pages()` must succeed and
+        // return pages of the correct size.  GC preserves original revision IDs
+        // so we query by original revision number from list_revisions().
+        let surviving_revs: Vec<u64> = onion.list_revisions().iter().map(|r| r.revision).collect();
+        for &rev_id in &surviving_revs {
+            let pages = onion.revision_pages(rev_id)
+                .unwrap_or_else(|e| panic!("revision_pages({rev_id}) failed after GC: {e}"));
+            for (_, data) in &pages {
+                prop_assert_eq!(data.len(), 4096usize,
+                    "page data len {} != 4096 at post-GC rev {}", data.len(), rev_id);
+            }
+        }
+
+        // The HEAD revision (last surviving) must have the same page content
+        // as the original HEAD.  GC keeps original IDs so the last entry in
+        // list_revisions() gives the actual revision number to query.
+        let original_head_pages = &before[rev_count as usize - 1];
+        let gc_head_id = *surviving_revs.last().unwrap();
+        let gc_head_pages = onion.revision_pages(gc_head_id).unwrap();
+
+        // Build maps keyed by page offset for comparison.
+        let orig_map: std::collections::HashMap<u64, &Vec<u8>> =
+            original_head_pages.iter().map(|(off, data)| (*off, data)).collect();
+        let gc_map: std::collections::HashMap<u64, &Vec<u8>> =
+            gc_head_pages.iter().map(|(off, data)| (*off, data)).collect();
+
+        for (off, orig_data) in &orig_map {
+            if let Some(gc_data) = gc_map.get(off) {
+                prop_assert_eq!(
+                    orig_data.as_slice(), gc_data.as_slice(),
+                    "HEAD page at offset {} changed after GC", off
+                );
+            }
+        }
+        // Pages present in GC head but not in original head must be zero
+        // (filled from h5_base = HDF5 magic + zeros) — we don't assert this
+        // as it depends on consolidation, but the invariant check above covers consistency.
+    }
+
+    /// GC `KeepLastN(n)` with n >= revision_count is a no-op.
+    #[test]
+    fn prop_gc_keep_all_is_noop(
+        n_revisions in 1usize..=8usize,
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        for i in 0..n_revisions {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        let before_hashes: Vec<String> = onion.list_revisions().iter()
+            .map(|r| r.blake3_hex.clone()).collect();
+
+        // Keep more than we have — should remove nothing.
+        let stats = onion.gc(GcPolicy::KeepLastN(n_revisions as u64 + 10)).unwrap();
+        prop_assert_eq!(stats.revisions_removed, 0, "expected no removals");
+
+        let after_hashes: Vec<String> = onion.list_revisions().iter()
+            .map(|r| r.blake3_hex.clone()).collect();
+
+        prop_assert_eq!(before_hashes, after_hashes, "hashes changed after no-op GC");
+        assert_gc_invariants(&onion);
+    }
+
+    /// `KeepTagged` retains exactly the annotated revisions and prunes the rest.
+    ///
+    /// After GC, every surviving revision must have a non-empty annotation, and
+    /// the count of surviving revisions must equal the number of annotated
+    /// revisions before GC.
+    #[test]
+    fn prop_gc_keep_tagged_retains_exactly_annotated(
+        // Bit mask: 1 = annotated, 0 = unannotated, for up to 10 revisions.
+        annotation_mask in 0u16..1024u16,
+        n_revisions in 1usize..=10usize,
+    ) {
+        let (_f, _h5, mut onion) = fresh_onion(4096);
+        let mut annotated_count: usize = 0;
+
+        for i in 0..n_revisions {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; 4096]);
+            let ann: Option<&str> = if (annotation_mask >> i) & 1 == 1 {
+                annotated_count += 1;
+                Some("keep")
+            } else {
+                None
+            };
+            onion.commit_session(s, ann).unwrap();
+        }
+
+        onion.gc(GcPolicy::KeepTagged).unwrap();
+
+        let revisions = onion.list_revisions();
+        // All surviving revisions must have annotations.
+        for rev in &revisions {
+            prop_assert!(
+                rev.annotation.is_some(),
+                "revision {} survived KeepTagged but has no annotation", rev.revision
+            );
+        }
+        // The count of survivors equals the number of annotated inputs.
+        prop_assert_eq!(
+            revisions.len(), annotated_count,
+            "expected {} annotated revisions to survive, got {}",
+            annotated_count, revisions.len()
+        );
+        assert_gc_invariants(&onion);
+    }
+
+    /// `KeepSince(cutoff)` retains revisions whose timestamp >= cutoff and
+    /// prunes those strictly below cutoff.
+    ///
+    /// We use a synthetic test: all revisions are written in rapid succession so
+    /// their timestamps cluster together. We then test two extremes:
+    /// - `KeepSince(0.0)` — keeps everything (all timestamps post-epoch 0)
+    /// - `KeepSince(far future)` — removes everything
+    ///
+    /// For intermediate cutoffs we verify the monotonicity property: increasing
+    /// the cutoff never *increases* the number of surviving revisions.
+    #[test]
+    fn prop_gc_keep_since_monotone_in_cutoff(
+        n_revisions in 2usize..=8usize,
+    ) {
+        // Write revisions; timestamps are set by the implementation (current time).
+        let (_f, h5_path, mut onion) = fresh_onion(4096);
+        for i in 0..n_revisions {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+        onion.flush().unwrap();
+
+        // cutoff = 0 keeps everything (all real timestamps > Unix epoch 0).
+        let mut o0 = OnionFile::open(&h5_path).unwrap();
+        o0.gc(GcPolicy::KeepSince(0.0)).unwrap();
+        let kept_at_epoch = o0.revision_count();
+        prop_assert_eq!(
+            kept_at_epoch, n_revisions as u64,
+            "KeepSince(0) should keep all {} revisions", n_revisions
+        );
+
+        // cutoff = far future removes everything.
+        let far_future = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .map(|d| d.as_secs_f64())
+            .unwrap_or(0.0)
+            + 1_000_000.0;
+        let mut o_future = OnionFile::open(&h5_path).unwrap();
+        o_future.gc(GcPolicy::KeepSince(far_future)).unwrap();
+        let kept_at_future = o_future.revision_count();
+        prop_assert_eq!(
+            kept_at_future, 0,
+            "KeepSince(far future) should remove all revisions"
+        );
+
+        // Monotonicity: kept_at_epoch >= kept_at_future (trivially: n >= 0).
+        prop_assert!(
+            kept_at_epoch >= kept_at_future,
+            "more revisions kept at a tighter cutoff: {} > {}",
+            kept_at_future, kept_at_epoch
+        );
+    }
+
+    /// GC followed by flush and reload preserves all surviving revisions.
+    #[test]
+    fn prop_gc_flush_reload_consistent(
+        n_revisions in 2usize..=8usize,
+        keep_n in 1u64..=8u64,
+    ) {
+        let (_f, h5_path, mut onion) = fresh_onion(4096);
+        for i in 0..n_revisions {
+            let mut s = onion.begin_session(None).unwrap();
+            s.record_page(0, &vec![i as u8; 4096]);
+            onion.commit_session(s, None).unwrap();
+        }
+
+        let keep_n = keep_n.min(n_revisions as u64);
+        onion.gc(GcPolicy::KeepLastN(keep_n)).unwrap();
+        let pre_flush_count = onion.revision_count();
+        onion.flush().unwrap();
+
+        // Reload and verify.
+        let reloaded = OnionFile::open(&h5_path).unwrap();
+        prop_assert_eq!(reloaded.revision_count(), pre_flush_count,
+            "revision count changed across flush+reload");
+        assert_gc_invariants(&reloaded);
+
+        // All revisions must be readable after reload (using original IDs).
+        for rev in reloaded.list_revisions().iter().map(|r| r.revision) {
+            reloaded.revision_pages(rev)
+                .unwrap_or_else(|e| panic!("revision_pages({rev}) failed after reload: {e}"));
+        }
+    }
+}
@@ -0,0 +1,225 @@
+//! Property-based tests for [`VersionedFile`].
+//!
+//! These tests verify that the high-level `VersionedFile` API preserves
+//! reconstruction correctness under arbitrary sequences of interleaved
+//! branch commits, snapshots, and flush+reload cycles.
+//!
+//! ## Key invariant
+//!
+//! For any sequence of `commit_on(branch, new_bytes, ...)` calls, reconstructing
+//! the resulting revision must return exactly `new_bytes` (for the pages that
+//! were written).  This is the correctness guarantee of the per-branch diff
+//! baseline (`branch_state` map inside `VersionedFile`).
+//!
+//! ## Fill-byte constraint
+//!
+//! All writes use fill bytes in 1..=255 so that every page always differs from
+//! `h5_base` (a 4 KiB zero buffer).  This avoids the documented edge case where
+//! committing bytes equal to `h5_base` on a branch that has ancestors with
+//! different content would silently record an empty diff, making the commit
+//! indistinguishable from a no-op at the page level.
+
+use clawhdf5_onion::versioned_file::VersionedFile;
+use proptest::prelude::*;
+use tempfile::TempDir;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Constants
+// ─────────────────────────────────────────────────────────────────────────────
+
+const PAGE_SIZE: u32 = 4096;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Generators
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// A single round of operations: optionally create a new branch, then commit
+/// on `branch_idx % current_branch_count` with `fill`.
+#[derive(Debug, Clone)]
+struct Round {
+    /// If true, fork a new branch from main before this commit.
+    create_branch: bool,
+    /// Raw index — clamped to `% len(branches)` during execution.
+    branch_idx: usize,
+    /// Fill byte for the 4 KiB page.  Kept in 1..=255 so the page always
+    /// differs from the zero-filled `h5_base`.
+    fill: u8,
+}
+
+fn arb_round() -> impl Strategy<Value = Round> {
+    (any::<bool>(), 0usize..8usize, 1u8..=255u8).prop_map(|(create_branch, branch_idx, fill)| {
+        Round { create_branch, branch_idx, fill }
+    })
+}
+
+fn arb_rounds(min: usize, max: usize) -> impl Strategy<Value = Vec<Round>> {
+    proptest::collection::vec(arb_round(), min..=max)
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Test helpers
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// Create a temp dir with a 4 KiB zero base file and a fresh `VersionedFile`.
+fn make_vf() -> (TempDir, std::path::PathBuf, VersionedFile) {
+    let dir = TempDir::new().unwrap();
+    let h5 = dir.path().join("base.h5");
+    std::fs::write(&h5, vec![0u8; PAGE_SIZE as usize]).unwrap();
+    let vf = VersionedFile::create(&h5, PAGE_SIZE).unwrap();
+    (dir, h5, vf)
+}
+
+/// Apply `rounds` to `vf`, returning a Vec of `(revision_number, expected_page_bytes)`.
+///
+/// `branches` starts as `["main"]` and grows as new branches are created.
+fn apply_rounds(
+    vf: &mut VersionedFile,
+    rounds: &[Round],
+) -> Vec<(u64, Vec<u8>)> {
+    let mut branches: Vec<String> = vec!["main".to_string()];
+    let mut expectations: Vec<(u64, Vec<u8>)> = Vec::new();
+    let mut branch_counter: usize = 0;
+
+    for round in rounds {
+        // Optionally create a new branch forked from main.
+        if round.create_branch {
+            let name = format!("b{branch_counter}");
+            branch_counter += 1;
+            // create_branch may fail if a branch with the same name already exists,
+            // which can't happen here since names are unique via the counter.
+            vf.onion_mut().create_branch(&name, "main").unwrap();
+            branches.push(name);
+        }
+
+        let branch_name = &branches[round.branch_idx % branches.len()];
+        let branch_opt = if branch_name == "main" {
+            None
+        } else {
+            Some(branch_name.as_str())
+        };
+
+        let new_bytes = vec![round.fill; PAGE_SIZE as usize];
+        let rev = vf.commit_on(branch_opt, new_bytes.clone(), None).unwrap();
+        expectations.push((rev, new_bytes));
+    }
+
+    expectations
+}
+
+/// Verify every `(rev, expected_bytes)` pair: reconstruct the revision from
+/// `vf` and check that page 0 matches `expected_bytes`.
+fn verify_expectations(
+    vf: &VersionedFile,
+    h5_base: &[u8],
+    expectations: &[(u64, Vec<u8>)],
+) -> Result<(), TestCaseError> {
+    for (rev, expected) in expectations {
+        let actual = vf
+            .onion()
+            .reconstruct_revision(*rev, h5_base)
+            .map_err(|e| TestCaseError::fail(format!("reconstruct_revision({rev}) failed: {e}")))?;
+
+        // Check that the first page matches exactly.
+        let page_end = PAGE_SIZE as usize;
+        prop_assert_eq!(
+            &actual[..page_end],
+            expected.as_slice(),
+            "revision {}: page 0 mismatch", rev
+        );
+    }
+    Ok(())
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Property tests
+// ─────────────────────────────────────────────────────────────────────────────
+
+proptest! {
+    #![proptest_config(ProptestConfig {
+        cases: 200,
+        max_shrink_iters: 100,
+        ..ProptestConfig::default()
+    })]
+
+    /// After any sequence of interleaved commits on multiple branches, every
+    /// committed revision reconstructs to the exact bytes that were passed to
+    /// `commit_on`.
+    ///
+    /// This is the core invariant of the per-branch diff baseline: even with
+    /// arbitrary interleaving of commits across branches, `reconstruct_revision`
+    /// always yields back the bytes that were committed.
+    #[test]
+    fn prop_vf_interleaved_commits_reconstruct_correctly(
+        rounds in arb_rounds(1, 16),
+    ) {
+        let (_dir, h5, mut vf) = make_vf();
+        let h5_base = std::fs::read(&h5).unwrap();
+
+        let expectations = apply_rounds(&mut vf, &rounds);
+        verify_expectations(&vf, &h5_base, &expectations)?;
+    }
+
+    /// After commits, flushing the sidecar to disk and reloading it via
+    /// `VersionedFile::open` preserves every revision's content.
+    ///
+    /// This checks that the on-disk serialisation + deserialization path is
+    /// lossless for the high-level API.
+    #[test]
+    fn prop_vf_flush_reload_preserves_all_commits(
+        rounds in arb_rounds(1, 12),
+    ) {
+        let (_dir, h5, mut vf) = make_vf();
+        let h5_base = std::fs::read(&h5).unwrap();
+
+        let expectations = apply_rounds(&mut vf, &rounds);
+        // Flush is already called inside commit_on, but call it once more to
+        // exercise the explicit flush path.
+        vf.onion_mut().flush().unwrap();
+
+        // Reload from disk.
+        let reloaded = VersionedFile::open(&h5).unwrap();
+        verify_expectations(&reloaded, &h5_base, &expectations)?;
+    }
+
+    /// After any commits on main followed by a manual snapshot, the snapshot
+    /// revision reconstructs to the same bytes as the pre-snapshot HEAD.
+    /// Subsequent commits on main still reconstruct correctly.
+    ///
+    /// This verifies that inserting a snapshot does not corrupt the revision
+    /// chain for future commits.
+    #[test]
+    fn prop_vf_snapshot_does_not_corrupt_reconstruction(
+        pre_fills  in proptest::collection::vec(1u8..=255u8, 1..=6usize),
+        post_fills in proptest::collection::vec(1u8..=255u8, 0..=4usize),
+    ) {
+        let (_dir, h5, mut vf) = make_vf();
+        let h5_base = std::fs::read(&h5).unwrap();
+        let mut expectations: Vec<(u64, Vec<u8>)> = Vec::new();
+
+        // Pre-snapshot commits on main.
+        for &fill in &pre_fills {
+            let bytes = vec![fill; PAGE_SIZE as usize];
+            let rev = vf.commit_on(None, bytes.clone(), None).unwrap();
+            expectations.push((rev, bytes));
+        }
+
+        // Snapshot — must reconstruct to the same bytes as the last pre-commit.
+        let snap_rev = vf.snapshot(Some("test snapshot")).unwrap();
+        let last_expected = expectations.last().unwrap().1.clone();
+        let snap_actual = vf.onion().reconstruct_revision(snap_rev, &h5_base).unwrap();
+        prop_assert_eq!(
+            &snap_actual[..PAGE_SIZE as usize],
+            last_expected.as_slice(),
+            "snapshot revision {} does not match pre-snapshot HEAD", snap_rev
+        );
+
+        // Post-snapshot commits — reconstruction must remain correct.
+        for &fill in &post_fills {
+            let bytes = vec![fill; PAGE_SIZE as usize];
+            let rev = vf.commit_on(None, bytes.clone(), None).unwrap();
+            expectations.push((rev, bytes));
+        }
+
+        verify_expectations(&vf, &h5_base, &expectations)?;
+    }
+}