[Richard Lundeen (richlundeen)]

Description

#3499 raised the file-backed SQLite busy timeout to 30 s, but Windows CI still fails with database is locked (failed job). The same flake also hit test_concurrent_orm_score_deletions_clean_final_observation.

Cause. Each SQLite commit calls fsync, and the writer keeps the write lock during fsync. On loaded CI disks, fsync can take seconds. In the failed run, one fixture took 196 s to create 53 tables, about 3.7 s for each commit. Ten concurrent writers at that speed need about 37 s, so one writer waits past the 30 s busy timeout. A longer timeout does not fix slow commits.

Changes. Only test code changes. Production code and settings do not change.

• tests/unit/conftest.py sets PRAGMA synchronous=OFF when a unit test opens a SQLite connection. This removes fsync from file-backed test databases and makes their setup fast. Locking and transactions do not change. The PRAGMA must read the schema, so it runs with busy_timeout=0. If another connection holds an exclusive lock (the analytics lock tests do this on purpose), the new connection does not wait and keeps fsync.
• A SQLITE_BUSY error gets a note with the time that SQLite waited for the lock, for example SQLite returned SQLITE_BUSY after 30.15 s. A wait near the busy timeout shows lock contention. A wait near 0 s shows that SQLite did not wait.
• The two tests that failed in CI use the shared test watchdog (wait_for_completion_async) instead of 5–60 s wall-clock deadlines, as .github/instructions/test.instructions.md requires for correctness tests.

Other recent flakes have different causes and are not in this PR: short asyncio.wait_for deadlines on macOS (for example in test_fuzzer.py) and subprocess timeouts on Windows.

Tests and Documentation

New tests in tests/unit/memory/test_sqlite_fixtures.py:

• File-backed sync and async connections of SQLiteMemory report synchronous=0.
• A connection that opens during an exclusive lock of another connection does not wait, keeps its busy timeout, and keeps fsync.
• A SQLITE_BUSY error has the lock-wait note.

With the hooks removed, the first and third tests fail. Updated doc/contributing/5_unit_tests.md.

Validation on Windows, Python 3.14.2:

Command	Result
uv run --no-sync pre-commit run --all-files	All 18 hooks passed, including ty
uv run --no-sync python -m pytest -n 4 --dist=loadfile tests/unit -q -p no:cacheprovider --timeout=600 --durations=25 (before rebase on 246b659e4)	31580 passed, 50 skipped; no file-backed SQLite test in the 25 slowest
uv run --no-sync python -m pytest -n 4 --dist=loadfile tests/unit/memory tests/unit/backend/test_operations.py tests/unit/backend/test_analytics_lifecycle.py tests/unit/backend/test_analytics_benchmark.py -q -p no:cacheprovider --timeout=600 (after rebase)	1986 passed, 1 skipped
uv run --no-sync python -m pytest -n 4 --dist=loadfile <17 test files changed on main since the branch point> -q -p no:cacheprovider --timeout=600 (after rebase)	539 passed
uv run --no-sync python -m pytest <3 file-backed concurrency tests> -q -p no:cacheprovider --timeout=300, 5 times in each of 6 parallel jobs	30 of 30 runs passed; the 10-writer test takes about 0.4 s (58 s before the CI failure)
File-backed test modules with -n 4 (conftest, branching, observations, analytics lock retry, activity operation IDs, SQLite memory, cancellation, migration, backend file-backed tests)	488 passed in 74.9 s before, 491 passed in 60.9 s after

Commit latency on a local NVMe disk: synchronous=FULL 3.0 ms (7.2 ms with background fsync load), OFF 1.2 ms (2.35 ms). CI disks gain more, because fsync is the slow part there.

JupyText: not run. This PR does not change notebooks, documentation code, or APIs.