Agentic Settlement Protocol: An Application Profile for Refundable, Delayed-Fulfilment Agent Commerce on Stablecoin Rails

Abstract: Autonomous agents can already pay per request: HTTP-native protocols such as x402 let an agent sign a stablecoin authorization and receive a resource in the same round trip. That model is atomic and final, which suits metered access and fails commerce: a purchase made on a person's behalf -- a service appointment, a physical order, a flight -- is large, frequently cancelled, and should not become the seller's money until delivery. We present the Agentic Settlement Protocol (ASP), an application profile over on-chain authorize-and-capture escrow (as standardised by the Commerce Payments Protocol) for businesses whose fulfilment is confirmed off-chain by their own order, scheduling, invoicing or booking system, abstracted as a fulfilment engine. ASP contributes: a three-deadline hold model separating the issuance deadline, escrow expiry and the engine's inventory expiry by an explicit submission-inclusion-finality margin, under which no inventory is issued against reclaimable funds; a fulfilment-verification ladder stating who is trusted to trigger capture, what their attestation proves, and under what challenge window; engine-authoritative partial refunds with a refund-liquidity order and per-seller exposure controls, including atomic exposure reservation, that bound the operator's credit risk; distributor revenue share that is provably unprofitable to self-deal; a single-currency-per-charge invariant; and a normative interface specification (x402 scheme, vault ABI, operator and connector APIs, conformance levels) intended to let independent implementations interoperate. The design originated in a review of travel-agency participation in agentic settlement and is instantiated on the XDC Network. This is a design paper; a fault-injection evaluation plan is specified and measurement is left to follow-up work.