[Arc Testnet quirk] eth_estimateGas returns data:null for complex calls — use hardcoded gasLimit

[osr21]

Symptom

On Arc Testnet, eth_estimateGas returns { data: null } or an unhelpful error for multi-step transactions (e.g. ERC-20 approve followed by a CCTP depositForBurn). ethers.js interprets this as a failed estimation and throws before the transaction is even submitted.

Affected calls

• usdc.approve(tokenMessenger, amount) — sometimes passes, sometimes fails estimation
• tokenMessenger.depositForBurn(...7 params) — consistently fails estimation on Arc Testnet
• Any call with complex state reads (multiple SLOADs) in the same block

Reproduction

const provider = new ethers.JsonRpcProvider('https://rpc.drpc.testnet.arc.network');
const messenger = new ethers.Contract(TOKEN_MESSENGER, ABI, provider);
// This throws: "estimateGas failed — data: null"
await messenger.estimateGas.depositForBurn(amount, domain, recipient, token, caller, maxFee, threshold);

Workaround

Supply an explicit gasLimit override so ethers.js skips estimation entirely:

const tx = await messenger.depositForBurn(...args, { gasLimit: 600_000n });

600k covers approve + CCTP burn comfortably. The actual gas used is typically 180–250k, so there's no waste — unused gas is refunded.

References

• Tracked in arc-node#80
• Implementation in this repo: ChainConfig.gasLimitOverride field in src/lib/chains.ts