test_supervisor_singleton_lock_acquired called mod.main() which, since ec004821, runs run_pending_tasks() before start_callosum_in_process. On a fresh tmp_path, every maint script is pending, so main() spawned 12 subprocesses (~1.5-2s under coverage) before reaching the stub that raises SystemExit(0). Under system load that overruns the 5s default pytest-timeout, producing the intermittent FAILED seen during full-suite runs. Monkeypatch run_pending_tasks to a no-op — the test is about flock acquisition, not migrations. Verified with 10 consecutive `make test` runs, all green. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>