docs: Circle AppKit v1.5.x kit.bridge() and kit.send() have no documented Arc Testnet integration path — only kit.swap() / estimateSwap() are viable

[osr21]

Summary

Circle AppKit v1.5.x (@circle-fin/app-kit) documents kit.bridge() and kit.send() as top-level primitives, but neither has a documented path for Arc Testnet. When building a swap DApp that needed cross-chain bridging (Ethereum Sepolia → Arc Testnet) and wallet-to-wallet token sends, only kit.swap() and kit.estimateSwap() worked reliably.

What we expected

The AppKit README implies that kit.bridge() enables USDC bridging between any two supported chains including Arc Testnet, and that kit.send() sends USDC/EURC between wallets on the same chain.

What actually happened

• kit.bridge() — No documentation on which chain identifiers are valid for Arc Testnet (e.g. "Arc_Testnet" string constant). The CCTP attestation service used internally does not document Arc Testnet support.
• kit.send() — No documentation on whether Arc Testnet is supported, or whether the underlying transfer is an on-chain ERC-20 transfer() or a Circle-mediated off-chain transfer.
• Both methods require the backend wallet private key to execute, which conflicts with the client-side viem adapter pattern shown in docs — creating a security/UX architecture mismatch.

Workaround

• Bridge: Guide users to faucet.circle.com manually. No programmatic on-chain bridge path was available.
• Send: Implemented a direct ERC-20 transfer() call via MetaMask + viem, bypassing AppKit entirely.

Environment

• @circle-fin/app-kit v1.5.0
• @circle-fin/adapter-viem-v2 v1.10.0
• Arc Testnet (Chain ID 5042002)
• Observed: May 2025

Request

Please add to the Arc developer docs:

1. Which AppKit methods are supported on Arc Testnet
2. The correct chain identifier string for Arc Testnet in kit.bridge()
3. Whether kit.send() is implemented for Arc Testnet or falls back to raw ERC-20

[osr21]

Confirmed findings + working alternative for cross-chain USDC bridging

Based on our experience building a bridge DApp on Arc Testnet:

What works:

• kit.swap() and kit.estimateSwap() work for same-chain USDC swaps on Arc Testnet
• For Arc Testnet ↔ Ethereum Sepolia/Base Sepolia/Avalanche Fuji bridging, CCTP V2 directly is the only fully documented path

What doesn't have an official Arc path:

• kit.bridge() — no documented Arc Testnet configuration in AppKit v1.5.x
• kit.send() — no documented Arc Testnet wallet-to-wallet send path

Working alternative for USDC bridging (CCTP V2):
The CCTP V2 contracts are live on Arc Testnet. All chains (Arc, Sepolia, Base Sepolia, Fuji) share the same contract addresses:

• TokenMessenger: 0x8FE6B999Dc680CcFDD5Bf7EB0974218be2542DAA
• MessageTransmitter: 0xE737e5cEBEEBa77EFE34D4aa090756590b1CE275

Arc Testnet's CCTP domain ID is 26. See docs/cctp-v2.md in PR #79 for a complete
integration guide including the Arc-specific minFinalityThreshold and attestation timing.