Figure 18.3: Receipts, not transcripts, are the system of record
Figure 18.3 Receipts, not transcripts, are the system of record. Up top, a naive
resume whose state says the step never ran sends the email a second time. Down
below, the same crash lands on a run that attached an idempotency key (in
accent) to the mutating call and carried the identical key into the retry; the
downstream service recognizes it and the email goes out exactly once.
