feat: implement Milestone 1 phases 1-3 — schema, WAL, and storage layer
Implements the foundation of tidalDB's data pipeline:
**Phase 1 – Schema primitives**
- EntityId newtype (u64, big-endian ordering)
- SignalTypeDefinition with pre-computed decay λ, deduped/sorted windows
- SchemaBuilder with full constraint validation (duplicates, identifiers,
half-life, windows, velocity)
- LumenError wrapping all subsystems with required From impls
**Phase 2 – Write-Ahead Log**
- Length-prefixed, BLAKE3-protected entry format
- Group-commit writer (batch up to 100 events / 10 ms)
- Double-buffered content-hash deduplication
- Checkpoint, truncation, and crash-recovery with full replay
- Integration, property, and UAT tests (incl. 5,500-event deterministic UAT)
- Proptest coverage scaled to 10 000 events/run (was ≤500) to meet
acceptance criterion; cases reduced 100→10 to keep runtime comparable
**Phase 3 – Storage engine**
- StorageEngine trait (get/put/delete/scan/batch/flush)
- Key encoding: [EntityId][0x00][Tag][suffix] with ordering/prefix helpers
- InMemoryBackend (BTreeMap + RwLock)
- FjallStorage with three isolated keyspaces and atomic batch helper
- Property tests for key ordering and round-trip correctness
Also adds planning docs for phases 4-5, research docs, architecture
overview, and roadmap updates.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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