Every JSON error includes error.code, error.message, and error.requestId. A catalog miss is 404 and never queues work.
Only POST /v1/discover consumes discovery quota. Catalog hits do not; accepted duplicate requests joining active work do.
{"error":{"code":"brand_not_found","message":"This domain is not in the published catalog. Submit it with POST /v1/discover.","requestId":"req_…"}}