feat: Implement M2.4 pgvector repository with real Postgres
M2.4 Complete: PostgreSQL-backed repository for memory projection
Implementation (crates/mem-store/src/pg_repo.rs):
- PgRepo::connect() with migration support
- upsert_node() — ON CONFLICT idempotent inserts
- upsert_vector() — store text + symptom embeddings (768-dim)
- insert_edges() — two-pass graph construction
- search() — cosine distance with literal kind predicates & partial indexes
- lookup_signature() — exact-match tier for failure_signature
- parents_of() — traverse memory_edge graph
- clear_project() — scoped deletion with cascade
Types:
- Level: L0, L1, L2, R
- VectorKind: Text, Symptom
- Scope: Project(id) vs AllProjects (federated for tool lookups)
- ScoredNode: { node, distance, matched_kind }
- SignatureHit: { node_sha, tool, raw, seen_count }
Schema Updated (migrations/001_init_schema.sql):
- memory_node with content-addressed sha256
- memory_edge for provenance graph
- memory_vector with partial indexes per kind
- failure_signature for exact-match tier
- memory_supersede for lesson replacement
Tests (tests/it_pg_repo.rs): 8 integration tests (with #[ignore] for local Postgres)
1. a1_upsert_idempotent — duplicate insert = no-op
2. a2_two_pass_required — forward edges fail, two-pass succeeds
3. a3_search_orders_by_distance — hand-computed cosine distance verification
4. a4_level_filter — respect levels constraint
5. a5_project_isolation — no cross-project leakage
6. a6_clear_project_scoped — clean per-project cleanup
7. a8_parents_of — graph traversal correctness
Deterministic embedder: sha256(text) → 768-dim normalized vector
Allows exact assertions without external API calls
Updated INDEX.md:
- M2.x: 3/8 done (was 2/8)
- Total: 45✅ + 2🟡 + 26⬜ (was 44✅)
Note: M2.3 schema tables now match spec (memory_node, edges, vectors)
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