revoke retrieval key

Create an organization-owned read-only key scoped to this prompt. Return its full secret only in the initial 201 response and persist only a cryptographic hash; never store the secret in an idempotency receipt. Within the receipt retention period, a retry with the same idempotency key and body creates no duplicate and returns 409 secret_unavailable with the existing key metadata in error.details.key, without a secret. If the original response was lost, explicitly revoke that key and create a replacement using a new idempotency key. Different-body reuse fails idempotency_conflict. No automatic expiry. Rotation creates a new key, then explicitly revokes the old one.