x402 Protocol Version 2 kept the scheme model but moved payment data into headers and renamed them: X-PAYMENT → PAYMENT-SIGNATURE, X-PAYMENT-RESPONSE → PAYMENT-RESPONSE, and requirements now live in a base64 PAYMENT-REQUIRED header as a client-selectable array. This linter checks a supplied header set / 402 body for exactly these deltas, plus CAIP-2 network id formatting, and declares a protocol_version so a future wire bump is a data re-pin, not a code change. Produces a §4 compliance_control OpenChainGraph artifact.
specs/x402-specification-v2.md (Protocol Version 2, 2025-12-09). Chains, assets, and schemes are plugins, so the scheme registry is not hard-coded here; verify current scheme/network support before relying on a pass. Compute-over-supplied-inputs only, nothing here initiates, routes, or settles a payment.