PostgreSQL Access Methods disabled - CREATE INDEX USING ruhnsw not available

[ruvnet]

Priority: High

Current Behavior

PostgreSQL access methods (HNSW, IVFFlat) are disabled. Users cannot use:

CREATE INDEX ON table USING ruhnsw (embedding ruvector_l2_ops);
CREATE INDEX ON table USING ruivfflat (embedding ruvector_l2_ops);

Root Cause

The pgrx access method API is not yet stable. Access method registration requires unsafe FFI that may change between pgrx versions.

Workaround

Users can use in-memory indexes via the Rust API or function calls, but not PostgreSQL's native indexing.

Technical Details

• Location: crates/ruvector-postgres/src/index/
• Blocked by: pgrx access method API stabilization

Acceptance Criteria

• Monitor pgrx releases for stable access method API
• Implement HNSW access method when API stabilizes
• Implement IVFFlat access method
• Add index operator classes (ruvector_l2_ops, ruvector_cosine_ops, etc.)
• Integration tests with CREATE INDEX

Impact

Critical for production use - without native indexes, vector search requires sequential scans.