Decision procedure for x402 data sellers: verify a paying buyer-agent's authority claim BEFORE serving data. Steps: pars

Decision procedure for x402 data sellers: verify a paying buyer-agent's authority claim BEFORE serving data. Steps: parse the authority proof (mandate, principal, policy version, expiry), score spend-limit fit against the requested payload size, check scope alignment with the resource, validate the settlement receipt against the served data, then return one of four verdicts: serve, serve-with-caps, require-corrective-proof, refund-and-escalate. Includes kill criteria (never serve on an expired