Infrastructure improvements:
- Fix benchmarks-ann Makefile: type=baseline -> type=vec0-flat (baseline
was never a valid INDEX_REGISTRY key)
- Add DiskANN + text primary key test: insert, KNN, delete, KNN
- Add rescore + text primary key test: insert, KNN, delete, KNN
- Add WAL concurrency test: reader sees snapshot isolation while
writer has an open transaction, KNN works on reader's snapshot
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
sqlite3_column_blob() returns NULL for zero-length blobs or on OOM.
Several call sites in rescore KNN and DiskANN node/vector read passed
the result directly to memcpy without checking, risking NULL deref on
corrupt or empty databases. IVF already had proper NULL checks.
Adds corruption regression tests that truncate shadow table blobs and
verify the query errors cleanly instead of crashing.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Add rescore index type: stores full-precision float vectors in a rowid-keyed
shadow table, quantizes to int8 for fast initial scan, then rescores top
candidates with original vectors. Includes config parser, shadow table
management, insert/delete support, KNN integration, compile flag
(SQLITE_VEC_ENABLE_RESCORE), fuzz targets, and tests.
