Pytest drops tests/web_admin conftest fixtures when a web_admin file is revisited non-adjacently in the argument list #273

Confirmed in the independent review of PR #262 with controlled runs (pre-existing test-infra broken window, not introduced by any PR in this effort).

Repro: uv run --no-sync pytest tests/web_admin/test_actor_stats.py tests/test_release_breaking_change_accuracy.py tests/web_admin/test_jobs.py → 59 passed, 28 ERRORS: every test_jobs.py test fails at setup with fixture 'stub_pool' not found / fixture 'make_app' not found; the available-fixture list contains the root tests/conftest.py fixtures but none of tests/web_admin/conftest.py's, including the autouse _dev_env.

Controls (all clean): single web_admin file; root-file-first ordering (pytest tests/test_release_breaking_change_accuracy.py tests/web_admin/test_actor_stats.py); three adjacent web_admin files (119 passed). The trigger is a tests/web_admin/ directory revisited non-adjacently in the argument list; pytest's conftest collection appears to cache/skip on directory revisits, silently gutting the revisited file's fixtures.

Practical consequence: any mixed command line of that shape fails in ways that look like code breakage, not harness breakage; it bit two independent agents' test runs in this effort before it was identified. make test/make test-fast (directory-scoped) are unaffected.

Filed per this effort's policy of tracking every finding. Direction: investigate pytest's conftest collection on arg-order directory revisits (likely a collection-cache interaction); a root-conftest assertion or a documented harness rule could pin it.