The model-cache temp-directory guard builds its fake home inside the temp directory

What is wrong¶

test_it_is_not_under_the_temp_directory builds its fake home from tmp_path — which is itself under the temp directory, because that is what tmp_path is for. So the path it asserts about is inside the very directory the assertion says it stays out of, and the test fails whatever the production code does.

FAILED tests/config/test_model_cache_home.py::test_it_is_not_under_the_temp_directory
AssertionError: assert PosixPath('/tmp') not in <PosixPath.parents>
  where PosixPath('/tmp/pytest-of-runner/pytest-0/test_it_is_not_under_the_temp_0/user/.docir/models')

Why nobody saw it¶

It passed on the machine it was written on. tempfile.gettempdir() reports /var/folders/…/T on macOS while tmp_path reports the symlink-resolved /private/var/folders/…/T, and in .parents compares path components, not filesystem identity — so the two never matched and the broken fixture stayed invisible. The test was green there for a reason unrelated to the property it asserts.

model_cache_home() is correct and always was. This is a defect in the guard.

Measured¶

CI on main has failed on this one test, and only this one, for every run since it landed in 08e909d (2026-09-18) — ten consecutive runs across five commits, each otherwise green through ruff, actionlint, ty, vulture, tach, contract-sync and 4572 other tests. Because the test step fails, the four store gates after it (reindex, doctor --strict, check --strict, the decisions notice) are skipped, so the branch's document integrity has not been checked by CI on any of those commits either.

A red main that stays red is the failure mode behind Opening a store with no index builds one, deferring the vectors's argument one level out: a gate nobody can distinguish from noise is a gate that stops being read.

Resolution¶

FIXED — the home is built from the filesystem root (Path(temp.anchor) / …) instead of from tmp_path, and both sides of the comparison are resolved so a symlinked temp directory cannot hide a mismatch again. A precondition assertion states the fixture's own requirement — the fake home sits outside the temp directory — so a later simplification back to tmp_path fails loudly on both platforms rather than only on Linux.

Verified by injecting the defect the guard exists to catch: model_cache_home() returning fastembed's tempfile.gettempdir()/fastembed_cache fails it.

This is the testing rule's own shape, arriving from the other side: a test that has never failed has not been shown to work, and this one had never passed anywhere it mattered.