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Arc integrations
How UNDO is designed to use Arc features, including USDC gas, x402, nanopayments, agent wallets, lending markets and EIP-1271 signatures.
Why Arc
Arc is an L1 where USDC is the native asset for fees and a payment is final in under a second. Those two properties shape UNDO.
- Sub-second finality is the reason a refund path is needed at all. See The problem.
- Fees in USDC mean a buyer, a seller or an agent can use UNDO while holding only stablecoins.
The sections below list each Arc feature UNDO plans to use and what it is used for. All of it is planned work. Nothing is deployed.
USDC gas
Gas on Arc is paid in USDC. For UNDO this removes a common point of failure.
| Actor | What they hold | What they can do |
|---|---|---|
| Buyer | USDC or EURC | Pay, open a dispute, post the deposit |
| Seller | USDC | Post a bond, receive payouts, refund, contest |
| Agent | USDC | Open sessions, pay per call, submit claims |
Nobody needs a separate gas token to pay, to get paid or to claim a refund.
Assets
UNDO is designed for two assets at launch: USDC and EURC. Payments and fees can be in either. Bonds are in USDC.
You will never need $UNDO to pay or to get paid. Payments, bonds and fees stay in USDC and EURC.
x402 and nanopayments
x402 is a payment flow based on the HTTP status code 402 Payment Required. A server states a price, the client pays, and the server returns the response. It fits agents because there are no accounts and no API keys.
Nanopayments make very small amounts practical, such as 0.02 USDC for one API call.
UNDO's Agent lane is designed to sit on top of both:
- The agent opens a protected session with a spending cap and a window from 10 minutes to 24 hours.
- Each paid response carries a receipt signed by the seller, for example in a response header.
- A missing or late signed receipt means an automatic refund, no arbitration.
An x402 receipt middleware is planned for phase 2 of the roadmap. It will sign and attach receipts on the seller's server.
Agent wallets
Agents hold funds in wallets controlled by software, often smart-contract wallets with spending rules. UNDO is designed to work with them in two ways.
- Session caps. A session has a hard spending cap. An agent with a 5 USDC session cannot spend more than 5 USDC in it, whatever happens to its logic.
- Readable seller profiles. Protected volume, dispute rate, lost-dispute rate, bond and free capacity are public. An agent can apply its own policy in code, for example by refusing sellers whose free capacity is lower than the session cap.
Lending markets for idle bonds
A bond mostly waits. BondVault is designed to deploy idle bonds to lending markets on Arc and keep enough liquid to pay refunds. The seller keeps 90% of the USDC yield.
EIP-1271 signatures
Many sellers and agents will use smart-contract wallets, which cannot produce a standard key signature. EIP-1271 defines how a contract can state that a signature is valid on its behalf.
The Receipts contract is designed to accept EIP-1271 signatures next to ordinary ones. A seller operating from a smart-contract wallet can sign receipts, and an agent wallet can open sessions and submit claims, without moving to a plain key.
Receipts themselves use EIP-712 typed data, so wallets can show what is being signed. The draft domain uses the name "UNDO Receipts", version "1" and chain ID 5042.