{
 "error": "signing_unavailable",
 "detail": "the composite signer key is not loaded; no envelope can be produced",
 "http_status": 503,
 "charged": false,
 "schema_version": "preflight_v3",
 "note": "total refusal: when signing is unavailable the service returns 503 before any component runs, no charge, no envelope, per fail-closed policy; an unsigned envelope is never emitted",
 "reason_codes": [
  "signing_unavailable"
 ]
}