docs: add CCTP V2 integration guide for Arc Testnet (closes #110)#127
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docs: add CCTP V2 integration guide for Arc Testnet (closes #110)#127zkasuran wants to merge 1 commit into
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Documents the Arc-specific details needed to move native USDC on and off Arc with CCTP V2, addressing circlefin#110: - Arc CCTP domain is 26 (verified against Circle's supported-blockchains list; the testnet shares the mainnet domain). - All Arc CCTP contracts are V2. The V1 depositForBurn selector (0x6fd3504e) reverts against the V2 TokenMessenger; the V2 selector is 0x8e0250ee. Both were checked by computing keccak of the signatures. - Burns sourced from Arc should use minFinalityThreshold 2000 (finalized); 1000 can leave the attestation stuck pending. - eth_estimateGas can return data:null for depositForBurn, so pass an explicit gasLimit. - How to fetch the attestation from the Iris API and the fee endpoint. Contract addresses are from Circle's EVM smart contracts reference and the TokenMessenger was confirmed to have code on Arc Testnet. Adds a link from the README documentation section.
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What this does
Adds a CCTP V2 integration guide at
docs/cctp-v2-integration.mdand links it from the README documentation section. It resolves #110.The guide documents the Arc-specific details a developer needs to move native USDC on and off Arc with Cross-Chain Transfer Protocol V2, which are not currently in this repo or obvious from Circle's general docs:
destinationDomainindepositForBurn.depositForBurnselector (0x6fd3504e) reverts against the V2 TokenMessenger. The V2 selector is0x8e0250ee. This trips up code ported from older Circle examples.minFinalityThreshold: 2000for burns sourced from Arc. 1000 (Fast Transfer) can leave the attestation stuckpending.eth_estimateGascan returndata: nullfordepositForBurn, so pass an explicitgasLimit(covered with the typical gas range).How I verified the values
0x8FE6…2DAAreturns contract code (2175 bytes) on Arc Testnet viaeth_getCode.depositForBurn(uint256,uint32,bytes32,address,bytes32,uint256,uint32)=0x8e0250ee, V1depositForBurn(uint256,uint32,bytes32,address)=0x6fd3504e.minFinalityThresholdsemantics (1000 = Fast/confirmed, 2000 = Standard/finalized): Circle's contract interfaces. The "use 2000 on Arc" guidance comes from the field report in docs: CCTP V2 integration on Arc Testnet — domain 26, minFinalityThreshold 2000, V1 selector incompatible #110; I documented it as Arc behavior, not as a Circle spec./v2/messages/{sourceDomain}and/v2/burn/USDC/fees/{src}/{dst}paths return well-formed responses against the sandbox host.Docs-only change, no code touched.
AI disclosure
This guide was prepared with help from Claude (Anthropic), which drafted the prose. Every value (domain, contract addresses, selectors, finality thresholds, API paths) was verified against Circle's official documentation, an on-chain
eth_getCodecall, a local keccak computation of the selectors, and live calls to the Iris sandbox API before submitting. The verification steps are listed above so they can be rechecked.