The build of branch-a slept one second while the test asserted, without any synchronization, that branch-b was still PENDING. Under CPU contention on the mih09 host the sleep could elapse first, so branch-b was already RUNNING or SUCCESS when the assertion ran. branch-a now blocks until the test creates a gate file, and the test first waits for branch-a to be RUNNING; the PENDING assertion no longer depends on timing. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>