x402 EIP-712 Digest Recomputer

Recomputes the EIP-712 typed-data digest for an EIP-3009 TransferWithAuthorization struct (the x402 payments rail's underlying authorization primitive): domain separator, struct hash, and the final keccak256(0x19 || 0x01 || domainSeparator || structHash) digest. All four EIP-712 domain fields (name, version, chainId, verifyingContract) are mandatory caller inputs and are never defaulted or guessed -- a guessed verifyingContract would defeat the entire point of domain separation. keccak256 comes from the already-vendored, pinned noble-curves/noble-hashes bundle; the EIP-712/EIP-3009 ABI encoding scheme is implemented directly as public-spec arithmetic on top of it, not hand-rolled crypto. Performs no signature recovery and no domain/nonce/window checks (see the sibling x402-signer-recovery-verifier and x402-domain-nonce-window-checker nodes) -- makes no claim about signature validity, on-chain settlement, or spend. Zero network calls; never a facilitator, proxy, gateway, or settlement relay.

Tool URL: https://ainumbers.co/chaingraph/art-590-x402-eip712-digest-recomputer.html