Future.any([Future.delayed(N), stopSignal.future]) left unfired Timers alive after stop() fired the signal — pending Timers kept the Dart event loop running and prevented the process from exiting, causing the E2E integration test to time out (exit 124) instead of exiting cleanly. Replace all four occurrences with an explicit Timer that completes the stop-signal and is cancelled in a finally block, so the Dart isolate can exit as soon as the sync loops are stopped. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>