Durable State: Checkpoints, Resume, and Side Effects

What should happen to a Desk run when the machine running it restarts at step 18?

The run had already done real work. It read four orders and the payment records, sent the customer two replies, and received the customer's agreement to a refund of 150 dollars. Step 18 was the refund call itself, and nobody knows whether the payment system received it before the machine stopped.

Starting the case again would repeat both replies and spend every token of the first 17 steps a second time