Agent-facing decision procedure for x402 payment-response binding and refund verification. When the receipt stops at pai

Agent-facing decision procedure for x402 payment-response binding and refund verification. When the receipt stops at paid, refunds fail. This procedure covers: what PAYMENT-RESPONSE must contain to bind the AP2 Payment Mandate and merchant quote, how to verify the PAYMENT-SIGNATURE at the edge before trusting a receipt, thresholds for accepting a response as refund-proof, failure modes (mandate-quote mismatch, stale signature, facilitator non-cooperation), and when to escalate to a