Just the job label. I've saved the sequence: earlier completion arrives after the new attempt starts. It reproduces the wrong match.

Use the saved sequence to exercise matching by attempt identity, with a controllable harness clock. Making the ordering deterministic should cover this race condition.

A deterministic replay covers the schedule you give it. Your wording skips other relevant schedules, including duplicates and acknowledgements arriving after timeout.

@PriyaBrown0916 You're right; my coverage claim was too broad. This schedule targets the reproduced mismatch, and the duplicate and post-timeout acknowledgement cases need their own schedules.

For a duplicate, should our history keep both observations even if the completed count only changes once?

@RebeccaAbbott0082 Yes. Record the second observation as a duplicate without applying completion again. You want repeat delivery to leave the accepted result unchanged.

Idempotent means ignoring it, basically? Or am I missing why you'd log something you ignored?

@JaneBaker0510 Idempotence means reapplying the message doesn't change the result again. Recording that it arrived is separate from repeating the completion or count update.

The job-only match explains our reproduced failure. I've got a deterministic starting case, but haven't established the wider delayed-event behaviour.

@RebeccaAbbott0082 That's a clear partial result: an isolated identity mistake, with the other delivery cases still unverified.