Replay Protection

Make Sensitive Operations Safe to Retry

A client sends a request to create a refund. The server completes the refund, but the response is lost when the connection closes. The client cannot tell whether the operation succeeded, so it retries. If the server treats the retry as a new operation, one uncertain network failure can become two refunds. The same pattern appears in credit transfers, invitation acceptance, provisioning, job submission, and other state-changing actions where repeating an effect has security or financial consequences.