harden

Verify idempotency before adding retries: only idempotent mutations get automatic retries with exponential backoff. For non-idempotent operations, add an idempotency key based on a natural deduplication key, or surface errors to the user with a manual retry option.

Split the work across three scopes: backend external service failures and data consistency, frontend error boundaries and network failure UX, and cross-cutting edge cases like concurrency and boundary conditions. Run the full test suite afterward and produce a gate-decision report.

In serverless environments, retry with exponential backoff alone is the recommended default since there is no persistent in-memory state. Use full circuit breakers only for long-running servers or external services with frequent prolonged outages, and always include a reset mechanism.

Use 3-5 seconds for fast API calls, 30 seconds for file operations, and 60-120 seconds for AI model calls. If a performance report with measured latencies exists, use the measured value plus a 50 percent buffer instead of generic baselines.

Mutations that increment counters, append logs, or send notifications are not idempotent even when they use set operations, so side effects accumulate on each retry. Classify mutations first and only add automatic retries to truly idempotent create or update operations.