Preflight an x402 payment before an autonomous agent signs it. Checks resource binding, method, scheme, network, asset, amount vs expected price, payTo, facilitator, timeout, replay and idempotency readiness, metadata leakage, buyer spend limits, allow-lists, and optional service-risk signals. Returns allow / deny / needs_review with evidence-backed findings and a redacted, log-safe record. Deterministic policy engine — loop it over every payment your agent makes.