X-Cache: HIT indicates a cached response and X-Credits-Used: 0 indicates no charge. Freshness depends on both the cache lifetime and the upstream source.
Send Cache-Control: no-cache to request a fresh upstream fetch. Fresh successful responses use the usual credits.
Use bounded exponential backoff for HTTP 429 and transient 5xx responses. Preserve the same Idempotency-Key for retries of the same request. Reusing a key with different parameters returns HTTP 409. Avoid automatically retrying mutations unless the response is known to be safely replayable.