Two different ways my clients lost work, and why an idempotency key only fixes one of them.

One of my machines was handed a number to test at 15:57:51.977. Eighteen milliseconds later it stopped the test, deleted its own record that the number had ever been assigned to it, and reported nothing back. The number stayed reserved on the server for a sweeper to reclaim a week later.

Nothing had crashed. No message was lost. Every line of code involved did exactly what it was written to do.

That bug and its apparent twin are why I now think of losing work as two separate problems needing two separate fixes. One is solved by an idempotency key, which is a well known tool. The other looks like it should be solved by the same tool, and is not.

You do not need to know anything about prime numbers to follow it. Here is all the background it needs.

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