Send this delivery again

A key of the caller's choosing, held 24 hours and scoped to the account, the method and the path. The same key with the same body replays the stored response with Idempotent-Replayed: true. The same key with a different body is a 409 idempotency_key_reuse. A request still running under the key is a 409 idempotency_in_progress. A key longer than 255 characters or holding control characters is a 422. A write whose record cannot be stored is still processed once, without the replay guarantee. A response carrying a secret is never replayed: the second request receives a 409 idempotency_secret_not_replayable.