ERC-2612 Permit Binding Verifier

Recomputes the EIP-712 typed-data digest for an ERC-2612 Permit struct (the gasless-approval rail used by USDC and other ERC-2612 tokens) from caller-supplied domain and message fields, recovers the ECDSA signer from a caller-supplied signature, and reports whether the recovered signer binds to the caller-claimed owner or names the diverging field. DAI's legacy permit (holder, spender, nonce, expiry, allowed) is a different struct this node does not verify. All four EIP-712 domain fields (name, version, chainId, verifyingContract) are mandatory inputs and are never defaulted or guessed -- a guessed verifyingContract would defeat domain separation. keccak256 and secp256k1 recovery come from the already-vendored, pinned noble-curves/noble-hashes bundle shared with the sibling art-590/art-591 x402 pair (no new vendoring); the EIP-712/ERC-2612 ABI encoding scheme is implemented directly as public-spec arithmetic on top of it. This node makes no claim about on-chain nonce freshness, current allowance state, or whether deadline has passed relative to now -- it states plainly what it never fetched. Zero network calls; never a facilitator, proxy, or settlement relay. Golden vectors are cross-checked against an independently re-implemented EIP-712 encoding path and real secp256k1 signatures, not round-trip self-tests alone.

Tool URL: https://ainumbers.co/chaingraph/art-612-erc2612-permit-binding-verifier.html