Add CRC32C checksums to WAL record format (v2), implement crash recovery
with automatic truncation of corrupt records, add feature-gated group commit
buffer for batched fsync under concurrent load, and implement log rotation
via segment files with global offset addressing.
Key changes:
- Record format v2: [len:u32][crc32c:u32][blake3:32][payload:N]
- recover_file() scans and truncates corrupt tail records
- GroupCommitBuffer batches fsync via MPSC channel (tokio feature gate)
- SegmentManager with binary search resolution and cursor-based cleanup
- Journal::read() auto-refreshes segments on miss for writer/reader split
- Split recovery.rs and key_codec.rs into directory modules for 500-line max
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Phase 1 delivers the complete durability and storage layer:
- WAL with crash recovery: Append-only journal with BLAKE3 checksums,
fsync guarantees, and proper seek-to-EOF on reopen
- Storage engine: sled-backed KVStore with scan_prefix for range queries
- Content-addressed storage: H:{hash}, V:{hash}, E:{hash} key patterns
- Ingestor: Background worker tailing WAL, writing to KV with 8-byte
aligned record headers for rkyv zero-copy deserialization
- Comprehensive tests: 31 tests covering crash recovery, round-trips,
and multi-cycle durability
New crates: stemedb-wal, stemedb-storage, stemedb-ingest
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
