The original system design appeared functional on paper but contained several critical silent failures. One bug involved a nonexistent PollStats.snapshot() method, causing observability to completely fail. Another issue was a TypeError when PollResult.down() was called with a detail argument, crashing error handlers silently. The backoff logic for rate limiting and timeouts was effectively dead code, leading to continuous CPU burning under load.A logic gap meant ten straight timeouts produced no alarm, falsely reporting the engine as healthy. Furthermore, a missing import for Generic was a NameError waiting to happen in type annotations. The hardened implementation addresses these by defining explicit method signatures and return types to prevent TypeError and NameError. It implements a proper snapshot method using __slots__ for predictable memory usage.The backoff logic now correctly triggers on TIMEOUT and RATE_LIMITED outcomes, enforcing delays. The "stuck" threshold now checks both empty counts and failure counts, ensuring alarms are triggered appropriately. Resource management was improved with deque(maxlen=500) to cap history and a single-actor loop to eliminate per-task overhead. Asynchronous task cleanup was fixed with asyncio.wait_for to prevent hanging shutdowns. Concurrent state mutation is prevented by using a single asyncio.Task, eliminating the need for locks. A 429 flood scenario dramatically shows the improved resilience, preventing infinite polling and excessive resource consumption. The bottom line is that incompleteness in system design is equivalent to being broken, just with a delayed failure.