You are talking about distributed systems, nobody expects to read "exactly once" delivery. If I read that on the docs, I consider that a huge red flag.

And the fact is that what you describe is a performance optimization, I still have to write my code so that it is idempotent, so that optimization does not affect me in any other way, because exactly once is not a thing.

All of this to say, I'm not even sure it's worth mentioning?