[spelech]

Fixes #54.

Changes

• Initialize and migrate the vector table and indexes in one transaction.
• Use a null-safe relation lookup for fresh tables and actual SQLAlchemy binds for regclass queries.
• Migrate legacy id primary keys to (collection_name, id) without hiding aborted transactions.
• Fail explicitly instead of dropping populated shared tables on dimension mismatch; allow dimension changes after an explicit coordinated clear.

Verification

• Native PostgreSQL regressions initially failed; native plus existing pgvector tests now pass: 40 passed.
• Covers fresh and legacy tables, null legacy collections, migration rollback, shared-ID collection isolation, search, counts, scoped deletion and dimension safety.
• Generated requirement inventory: 2 passed; release/link-integrity gate passed.
• Combined backend regression run: 70 passed, 1 skipped.
• With the companion readiness/cache/failure fixes: 2 full-profile checks passed using PostgreSQL metadata, pgvector, API-key authentication and text/scanned PDF ingestion, search, cache reuse, injected database write failure, rollback, retry and deletion.

Native tests use isolated schemas under TEST_POSTGRES_URL and a deterministic loopback embedding endpoint. No production data was modified. Full-suite and fresh-source-build acceptance are not claimed.