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Circle runs a hosted x402 facilitator for Arc at https://api.circle.com/v1/facilitator/x402, so the rail needs no relayer, no gas wallet and no key — it verifies the EIP-3009 authorization, screens both addresses, pays the gas and broadcasts. Auth is an ordinary bearer token, which facilitator_headers already covers, and the base URL carries a path, which checkFacilitatorURL already permits and NewCallbackVerifier already trims. Rail is an opaque CAIP-2 string and the gate never contacts a chain, so this is config, tests and chart only: no production Go changes and the non-custodial invariant is untouched. Values are taken from Circle's own /supported response. Note asset_name is "USDC" and not the "USD Coin" that Base and Polygon USDC use for the same field: a wrong value there yields an offer that validates and parses but can never be paid, because the client signs over a different EIP-712 domain and the facilitator's rejection names no field. The asset address is the ERC-20 view of native USDC at six decimals; the same funds are eighteen decimals natively, which is only a trap for an operator reading a balance over rpc_url, since the gate never calls it. Arc gets its own single-rail test fixture rather than becoming a third rail in payGateTwoFacilitators, so the two-rail premise of TestOfferHeaderFitsDefaultProxyBuffers and the header budget in docs/nginx.md both stay intact. The chart block stays commented: the sidecar runs readOnlyRootFilesystem with only a read-only ConfigMap mount, so the bbolt grant ledger has nowhere to live, and CIRCLE_API_KEY is not wired from a Secret. Both are injection policy changes. Still unverified with a real credential: whether Circle additionally requires the Facilitator-Seller-Proof EIP-712 header on /settle, and whether it echoes network verbatim as eip155:5042 — callback.go compares that as an exact string, and a mismatch turns every settlement Ambiguous.
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Circle runs a hosted x402 facilitator for Arc at https://api.circle.com/v1/facilitator/x402, so the rail needs no relayer, no gas wallet and no key — it verifies the EIP-3009 authorization, screens both addresses, pays the gas and broadcasts. Auth is an ordinary bearer token, which facilitator_headers already covers, and the base URL carries a path, which checkFacilitatorURL already permits and NewCallbackVerifier already trims. Rail is an opaque CAIP-2 string and the gate never contacts a chain, so this is config, tests and chart only: no production Go changes and the non-custodial invariant is untouched.
Values are taken from Circle's own /supported response. Note asset_name is "USDC" and not the "USD Coin" that Base and Polygon USDC use for the same field: a wrong value there yields an offer that validates and parses but can never be paid, because the client signs over a different EIP-712 domain and the facilitator's rejection names no field. The asset address is the ERC-20 view of native USDC at six decimals; the same funds are eighteen decimals natively, which is only a trap for an operator reading a balance over rpc_url, since the gate never calls it.
Arc gets its own single-rail test fixture rather than becoming a third rail in payGateTwoFacilitators, so the two-rail premise of TestOfferHeaderFitsDefaultProxyBuffers and the header budget in docs/nginx.md both stay intact.
The chart block stays commented: the sidecar runs readOnlyRootFilesystem with only a read-only ConfigMap mount, so the bbolt grant ledger has nowhere to live, and CIRCLE_API_KEY is not wired from a Secret. Both are injection policy changes.
Still unverified with a real credential: whether Circle additionally requires the Facilitator-Seller-Proof EIP-712 header on /settle, and whether it echoes network verbatim as eip155:5042 — callback.go compares that as an exact string, and a mismatch turns every settlement Ambiguous.