UCP Checkout Payload Lint

Deterministic, verify-only structural lint of a caller-supplied Universal Commerce Protocol (UCP; Google + Shopify, announced NRF 2026-01-11, Apache-2.0 spec on GitHub) checkout resource against the schema pinned at tag v2026-04-08 of github.com/Universal-Commerce-Protocol/ucp. Checks the resource-level required[] field set, the status enum, ISO 4217 currency form, integer minor-unit amounts, and the exactly-one-subtotal / exactly-one-total cardinality rule on totals[]. Verdict CONFORMANT | NONCONFORMANT | UNKNOWN_VERSION: a payload declaring a UCP version outside the pinned allowlist is capped at UNKNOWN_VERSION regardless of otherwise-clean structure, never upgraded to CONFORMANT for a version this kernel has no pinned rules for. Never contacts a UCP or ACP endpoint and never fetches a live spec version -- the caller supplies the payload. UCP composes with AP2 rather than competing with it; part of the agentic-commerce-convergence chain alongside art-12 (ACP checkout conformance) and art-01 (AP2 mandate-chain validator).

Tool URL: https://ainumbers.co/chaingraph/art-564-ucp-checkout-payload-lint.html