ShipmentNotifier

Tells the buyer of a shipped order that it is on its way. The notification service is a remote call that may be slow or briefly down, so the reactor gives it its own budget: five attempts, from one second apart up to thirty, and ten seconds for each, before the order is parked for the handler in the failure ledger. A buyer the service does not know is a failure no retry can fix, so it parks the order at once.

A reactor starts at the end of the log: deploying it does not notify the buyers of the orders shipped before.