Looks like pure philosophical distinction. The question here would be who "you" are. Are "you" the low-level system processing raw messages, or are "you" a sys

Looks like pure philosophical distinction. The question here would be who "you" are. Are "you" the low-level system processing raw messages, or are "you" a system on top of that? The high-level system can rightfully claim to that it receives messages "exactly once"—from the low-level system.