Fix FTS5 recall for long multi-keyword searches

[EtanHey]

Summary

• switch FTS5 auto query escaping to use implicit AND for 1-3 terms and OR for 4+ terms
• add a regression test proving hybrid_search() returns a result for owner profile career work history years experience when semantic search contributes nothing
• update helper expectations so long multi-word searches no longer collapse to zero lexical matches

Test plan

• pytest tests/test_search_gaps.py
• pytest tests/test_search_gaps.py -k 'fts5_long_query_uses_or or hybrid_search_long_query_uses_fts_or_and_returns_results'
• pytest tests/test_phase6_critical.py -q (fails in unrelated compact-format test)
• pytest tests/test_enrichment_controller.py -q (fails in unrelated enrichment-controller tests)
• pytest tests/test_vector_store.py -q (errors due apsw.BusyError: database is locked on live DB fixture)
• pytest tests/ (repo-wide suite has many pre-existing unrelated failures/errors outside this change)

Notes

• Full repo tests are not currently green in this environment, so this PR is scoped to the FTS fix plus regression coverage.
• Unrelated local worktree changes in brain-bar/build-app.sh and 2026-03-29-174250-read-collab-gitsorchestratorcollabphase5-har.txt were intentionally left out.

Note

Fix FTS5 recall for long multi-keyword searches by switching to OR matching for 4+ terms

• In auto mode, _escape_fts5_query now joins quoted terms with OR when there are 4 or more terms, instead of implicit AND (space-separated). Queries with 3 or fewer terms retain AND behavior.
• Behavioral Change: auto mode results for long queries will broaden — documents matching any term are returned instead of only documents matching all terms.

^{Macroscope summarized 5f951a4.}

Summary by CodeRabbit

• Bug Fixes
  • Improved search recall for long multi-word queries (4+ terms) to help you find more relevant results.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 803cb9ba-e31d-41a0-97ef-39022d4f66a2

📥 Commits

Reviewing files that changed from the base of the PR and between 679236a and 5f951a4.

📒 Files selected for processing (2)

• src/brainlayer/_helpers.py
• tests/test_search_gaps.py

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📝 Walkthrough

Walkthrough

The PR modifies FTS5 query escaping logic to switch from implicit AND to OR-based term joining when "auto" mode processes 4+ terms, while preserving implicit AND behavior for shorter queries. Corresponding test expectations are updated to verify the new behavior.

Changes

Cohort / File(s)	Summary
FTS5 Auto Mode Logic src/brainlayer/_helpers.py	Added conditional branch in _escape_fts5_query to join escaped FTS5 terms with " OR " for 4+ terms in "auto" mode; updated docstring and inline comments to reflect the new joiner selection logic.
Test Updates tests/test_search_gaps.py	Renamed test class to TestFts5AutoMode and updated docstring. Modified long-query assertions to expect OR-joined terms instead of implicit AND. Added new test test_hybrid_search_long_query_uses_fts_or_and_returns_results to verify hybrid search behavior with long multi-keyword queries.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• feat: search hardening phase 1 — indexes, tag table, FTS5, compact importance #71: Directly modifies _escape_fts5_query "auto" mode to switch from implicit AND to OR joins for 4+ term queries, identical core change.

Poem

🐰 Long queries now leap with OR instead of AND,
Four terms or more, a scattered brand!
Short hops still shuffle through the space,
FTS5's search finds its new pace! ✨

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/fts5-long-query-recall

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