* feat(memory): DuckDB FTS BM25 search for knowledge items (#121)
Replaces `title ILIKE '%q%' OR content ILIKE '%q%'` ranked by
insertion order with BM25 relevance ranking via the DuckDB `fts`
extension. Czech queries like `cesky` match documents containing
`česky` (`strip_accents=1` + `lower=1`).
Architecture:
- src/fts.py — ensure_fts_loaded / ensure_knowledge_fts_index helpers.
The extension is per-connection (INSTALL persisted at engine level,
LOAD per-conn). Both helpers are idempotent and soft-fail on
unavailability with a logged WARNING.
- Schema v47 (_v46_to_v47) — builds the initial BM25 index over
knowledge_items(title, content) keyed by id. Migration is
best-effort against ANY exception (not just duckdb.Error) so the
schema bump cannot get stuck on v46 if a non-DuckDB error escapes
the helper.
- KnowledgeRepository.search — FTS-or-ILIKE dichotomy with execute-
time fallback. Same filter surface (statuses / category / domain /
source_type / personal / audience / dismissed) either way.
ensure_fts_loaded() returning True only guarantees the extension is
loadable, NOT that the index exists — migration soft-fail or a
concurrent overwrite=1 rebuild's drop-then-create window leaves the
extension loaded but the index missing. The BM25 execute is wrapped
in try/except duckdb.Error → ILIKE retry so transient failures
cannot 500 the /api/memory?search= endpoint.
- KnowledgeRepository.count_items — mirrors the same FTS-or-ILIKE
decision tree plus the execute-time fallback so the count always
matches the paginated result set.
- Per-mutation rebuild — create and title-or-content update rebuild
the index via overwrite=1 PRAGMA. Status flips skip (token stream
unchanged).
- app/main.py lifespan rebuilds once at boot as a safety net for
instances already on v47 across restarts.
- bm25_score column shape: ILIKE fallback now selects
`NULL AS bm25_score` so the result column set matches the FTS
path. Consumers can read the score uniformly; absence of relevance
ranking is signalled by the column being None everywhere, not
missing.
Tests in tests/test_knowledge_fts_search.py (9 tests):
- BM25 multi-term match set + adversarial-review fix asserting
higher-density doc ranks first (skipped if extension unavailable).
- bm25_score column attached when extension available.
- ILIKE fallback path on search + count_items via patched
ensure_fts_loaded → False; bm25_score is None on this path.
- Adversarial-review fix: search and count_items also fall back when
the extension is loaded but the index is missing (simulated via
drop_fts_index PRAGMA — the exact production failure mode the
fallback guards against).
- Index rebuild on create (new item searchable immediately).
- Title update re-surfaces row under new term, drops old.
- Czech-diacritic round-trip (cesky query → česky doc).
Pinned schema-version asserts bumped 46 → 47 (test_db_schema_version,
test_home_stats, test_schema_v42_migration, test_schema_v46_migration).
Closes#121.
* release: 0.54.20 — Corporate Memory BM25 search + All-Items bulk-edit batch bar
