Add exact scheme extension 7710

[danfinlay]

Description

Adds a new payment method for the exact scheme utilizing ERC-7710 account permissions, per the request by @phdargen. Allows payment in any token from accounts that expose this simple and flexible interface. Also allows payments to be made by permitted agents, including AI agents.

Tests

Just a specification for now, but tests can be added in the implementation phase.

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[vercel]

@danfinlay is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.