Adds a second external storage backend (Postgres/pgvector) alongside Qdrant
to prove the BaseBackend/BaseCollection contract generalizes across substrates
(SQL + JSONB containment filters + pgvector `<=>` ranking vs Qdrant's REST/dict
model), and addresses the review feedback on PR #1679.
Backend (mempalace/backends/pgvector.py):
- table-per-(namespace, palace, collection) isolation; advertises
supports_namespace_isolation
- JSONB filter pushdown for the containment subset, local-exact fallback for
$or/$contains/comparisons/where_document
- BM25 lexical search; marker-based mismatch protection
- optional psycopg dependency (lazy import), in-memory fake for CI, live test
gated on MEMPALACE_PGVECTOR_LIVE_URL
- registered in registry/__init__/pyproject entry point + [pgvector] extra;
MEMPALACE_PGVECTOR_DSN / MEMPALACE_PGVECTOR_NAMESPACE config; README docs
Isolation contract (RFC 001):
- PalaceRef/BaseBackend document the per-id MUST and the cross-namespace MUST,
gated on the new supports_namespace_isolation capability token
- runnable conformance suite (tests/_backend_conformance.py,
tests/test_backend_conformance.py); qdrant + pgvector run it via their fakes
Marker fail-loud guard:
- qdrant and pgvector now refuse get_collection when local_path is None instead
of silently opening a remote collection with no mismatch protection
Review fixes:
- palace._open_collection_or_explain handles unknown-backend KeyError as a CLI
state message instead of an escaping stack trace
- dedup.py docstring no longer claims "No API calls" unconditionally (false for
remote backends)
