Read The Fine Print

A broker vendor's landing page says: "Exactly-once delivery, guaranteed. Your consumers will never see a duplicate." You are evaluating it for a payments pipeline and you get one follow-up question with their engineer.

Which question is most likely to determine whether the claim survives contact with your system?

Is ordering guaranteed across the whole topic, or only within a single stream or partition

What happens when a consumer performs its side effect, then dies before its acknowledgement is durable, and a second consumer in the group takes over that stream

How many nodes must acknowledge a write before the broker reports the publish as successful

Does the producer client attach a sequence number so the broker can discard a resend after a network timeout