Restore three `_pin_hnsw_threads` tests that the previous integrity-gate
commit deleted. The function is still live code on develop (defined at
chroma.py:207, called from chroma.py:705 + mcp_server.py), so the
deletion left the import unused (ruff F401) and dropped coverage on a
function unrelated to this PR's scope. Restored verbatim from main.
Plus three nits @igorls flagged:
- **Thread-safety doc**: `_quarantined_paths` mutation is lock-free;
documented that idempotency of `quarantine_stale_hnsw` is the safety
property (concurrent same-palace calls produce a benign redundant
rename attempt that no-ops, no need for a lock).
- **Pickle protocol assumption**: `_segment_appears_healthy` requires
PROTO ≥ 2 (`0x80`). Documented; matches what chromadb writes today,
and a future protocol-0/1 emission would conservatively quarantine
+ lazy-rebuild rather than mis-classify as healthy.
- Class-level vs module-level scope: keeping class-level — the
conftest reset is the controlled case, and module-level wouldn't
remove the foot-gun, just relocate it. Conftest reset documented in
the existing comment is the right pattern for test isolation.
Style nit (`Path(marker).touch()` vs `open(marker, "a").close()`)
deferred — that pattern lives in #1177's territory, not #1173's.
37/37 tests pass on the PR branch.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
jp
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