Arc Relay Bridge — open-source CCTP V2 bridge + USDC paymaster reference for Arc Testnet

[osr21]

Arc Relay Bridge — open-source CCTP V2 bridge + USDC paymaster for Arc Testnet

Repo: https://github.com/osr21/arc-relay-bridge
Release: https://github.com/osr21/arc-relay-bridge/releases/tag/v1.0.0

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What it is

A standalone, frontend-only cross-chain USDC bridge built directly on CCTP V2 — no SDK wrapper, no backend DB, no wrapped tokens. Users connect MetaMask, pick source/destination chain, and move native USDC in a 4-step flow (Approve → Burn → Attest → Mint).

Supported chains: Arc Testnet ↔ Ethereum Sepolia ↔ Base Sepolia ↔ Avalanche Fuji

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What makes it different from the existing sample apps

The 5 apps in the gallery cover payments, escrow, and treasury — none covers bridging. This fills that gap with a full CCTP V2 reference: 7-param depositForBurn, per-chain minFinalityThreshold, and Circle Iris attestation polling.

It also ships three pieces of infrastructure not yet deployed anywhere else on Arc Testnet:

Component	What it does	Arc Testnet contract
GasRelayer	Covers the CCTP mint fee from the bridged amount — no destination gas required	0xf89773D7d9C43c01203793bf991e2550975a0C49
USDC Paymaster (ERC-4337 v0.7)	First USDC-denominated paymaster on Arc Testnet — pay gas in USDC, not ETH	0xEE39e1690F1bE07e8a68813f57cE3142197CECf6
YieldVault	On-chain USDC yield vaults across all 4 chains (Arc: 18.5% APY)	0xFf8f0Fc1Cca51ddE49ee1E7083D36CC99Af01665

All contracts compiled with evmVersion: "paris" (no PUSH0) and single-immutable (0x60a0) init — compatible with Arc's EVM constraints.

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Key technical notes for Arc builders

• All chains use CCTP V2 — the 7-param depositForBurn (selector 0x8e0250ee). V1 4-param selector will require(false) on these contracts.
• Arc minFinalityThreshold: 2000 (finalized); all others: 1000 (safe, ~1–2 min attestation).
• validatePaymasterUserOp must NOT use nonReentrant — global _locked storage writes violate ERC-7562 for unstaked paymasters and cause silent Pimlico rejections.
• 2-immutable init (0x60c0) silently reverts on Arc/Base/Fuji — keep any second constructor var as constant.

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Question for the team

Is there a process for submitting community apps to the sample apps gallery? The gallery currently has 5 great apps but nothing covering CCTP bridging — happy to adapt it to better fit the reference implementation format.

Also interested in the AMP design partner program — the GasRelayer here is conceptually related to what AMP describes at the protocol level.