Introduced on day 52
Idempotency key
A client-chosen identifier sent with every attempt of one intended action, so the service performs the action once and returns the stored result for repeats.
In detail
The key names the intent, not the attempt: generate it once per action (for example run id plus step number) and reuse it on each retry. Services store keys for a limited window and should reject the same key with a different body. Without a key, or a read-back before retrying, a timeout on a write leaves the caller unable to retry safely.