A warehouse event can arrive twice, arrive late or disappear from the consumer's view. Each failure changes what software believes is available. This session uses a small synthetic inventory stream to show the difference between delivery guarantees and correct state.

We follow a naive consumer, add persistent deduplication, then introduce an authoritative snapshot with a source sequence watermark. A delayed event arriving after that snapshot provides a concrete test of whether recovery counts the same movement twice.

The example also exposes a detection limit. A missing final event can leave the projection wrong while the sequence gap list is empty. The discussion covers what a snapshot must guarantee, which events it covers, and why physical counts still need their own reconciliation process.

Attendees will be able to explain where duplicate suppression belongs, design a recovery test around a watermark, and identify situations that a gap detector cannot observe. The demonstration uses synthetic data and makes no claims about an employer's architecture or results.

Available for consideration. Proposed duration is 30 minutes, with 10 minutes for questions. Intended for backend engineers and engineering leaders working with operational systems.