I knew the term from a discussion on GitHub (and had to google it back then), but I had used idempotency for years before — just without knowing that there's a word for it. That's probably the case for a lot of, if not most programmers who don't know idempotency.
(FWIW that's one of the greatest advantages of studying Computer Science in my opinion — programmers without a CS background often use the same concepts, but CS people know their names, which is basically a superpower.)
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