AP2 CartMandate Hash-Chain Builder

Builds an illustrative Google AP2 CartMandate Verifiable Digital Credential (VDC) skeleton whose credentialSubject carries a deterministic hash-chain over an ordered list of cart line items: link_0 = keccak256(canon({index:0,item})), link_i = keccak256(canon({index:i,item,prev:link_(i-1)})), cart_root = the final link. Reuses this repo's existing RFC 8785/JCS canonicalization (cgCanon) and the already-vendored @noble/hashes keccak256 bundle -- no new vendoring, no hand-rolled canonicalization or hashing. Stands beside art-16 (Google AP2 Mandate Builder) as a new node -- art-16's flat CheckoutMandate/PaymentMandate shape has no line-item array to chain over. An intact chain proves the ordered cart_items list was not altered after the chain was built; it does NOT prove human authorisation, delivery, settlement, or that item prices are correct or current. Given a prior chain's per-item links (claimed_links) and a possibly tampered cart_items, the kernel recomputes and reports whether the chain is intact plus the earliest divergent index, never a thrown exception. Zero network calls; never a facilitator, proxy, gateway, or settlement relay.

Tool URL: https://ainumbers.co/chaingraph/art-595-ap2-cartmandate-hashchain-builder.html