Common status code patterns
200/201: successful read or mutation.400: invalid payload or missing required fields.401: authentication missing or invalid.404: resource not found.409: state conflict (when route-specific logic enforces uniqueness/state).500: unexpected server-side failure.
Error handling guidance
- Treat all writes as potentially retriable only when idempotency is guaranteed by route semantics.
- Surface response body messages in client logs for operational debugging.
- Prefer route-specific error handling over global assumptions.
