AP2 mandate validation for production payments

What the protocol establishes

AP2 defines a mandate-centered trust model for agent payments. A production control must verify the relevant credential and then evaluate whether the exact checkout still fits the authority the user granted.

Five checks before execution

1. Verify the mandate credential and its trusted issuer.
2. Bind the payment mandate to the intended cart or checkout facts.
3. Compare final amount, currency and merchant with approved scope.
4. Require current consent and reject expired authority.
5. Atomically consume each idempotency key once.

The gap MandateShield closes

A cryptographically valid mandate can still be unsafe when the final price, seller or checkout context changed after authorization.

MandateShield normalizes execution facts and returns a deterministic decision with exact findings and a tamper-evident receipt. It complements protocol-native signature verification; it does not replace it.