x402 atomic-asset verification before payment

What the protocol establishes

The hosted bridge maps a selected x402 v2 PAYMENT-REQUIRED offer into a non-executable verification projection and never handles a payment credential. The optional first-party customer-side exact/EIP-3009 Gate can create one payload through the customer's compatible client, verify its signer locally, submit the bound HTTP request once and reconcile canonical chain evidence. It is not a facilitator or hosted settlement service.

Five checks before execution

1. Normalize the selected payment requirement into the final verification envelope.
2. Send atomic_units as a canonical decimal string and compare it with the registered cap using exact integer semantics.
3. Match asset_id, network, resource and asset_decimals exactly to the registered mandate.
4. Bind the payee and consume a stable payment-attempt identifier once.
5. Require the complete live authorization invariant before constructing or submitting payment.
6. For the optional exact/EIP-3009 Gate, persist the signed payload before transmission and commit only from fully bound canonical chain proof.

The gap MandateShield closes

A numerically rounded amount or a substituted asset, network, resource or decimal exponent can change what the user buys. A valid x402 flow is not by itself user authorization.

MandateShield normalizes execution facts and returns a deterministic decision with exact findings. Strict v2 verifies supported evidence and returns an ES256-signed receipt with public transparency; it complements the protocol's wider trust and settlement chain.