PermissionError [WinError 32] on Windows when Path.unlink() runs while
chromadb.PersistentClient still holds a handle on chroma.sqlite3. Rewrite
test_chroma_cache_invalidates_when_db_file_missing to prime
backend._clients/_freshness with a sentinel object instead of opening a
real PersistentClient, so the unlink runs against an unheld file.
The assertion is also corrected: after invalidation, ChromaBackend's
_client rebuilds a fresh PersistentClient which re-creates chroma.sqlite3
and re-stats it, so freshness ends up at the post-rebuild stat (not
(0, 0.0) as the assertion previously expected). The meaningful invariant
is "freshness advanced past the pre-unlink value AND the sentinel was
replaced", which the test now checks.
Ref: Windows CI failure on 995.
Igor Lins e Silva
61dd6e7d9c