bug: eth_gasPrice returns stale baseline — ERC-20 approve() rejects with "replacement transaction underpriced" without ≥30% gas price premium

[osr21]

Summary

When building a token swap DApp on Arc Testnet using viem, every ERC-20 approve() call fails with "replacement transaction underpriced" unless the caller manually fetches the live gas price and applies at least a 30% upward bump before submitting.

This is separate from #80 (gasLimit override) — the issue here is specifically gasPrice (EIP-1559-style replacement threshold) not gasLimit.

Steps to reproduce

1. Connect to Arc Testnet via createPublicClient / createWalletClient with viem
2. Call walletClient.writeContract({ functionName: "approve", ... }) without an explicit gasPrice
3. Transaction is submitted but immediately rejected by the node with:

   replacement transaction underpriced
   

Workaround

Fetch the live gas price and apply a 30% premium before every write:

const networkGasPrice = await publicClient.getGasPrice();
const gasPrice = (networkGasPrice * 130n) / 100n;

await walletClient.writeContract({
  ...
  gasPrice, // must be explicit
});

This applies to every ERC-20 write on Arc Testnet — approve(), transfer(), etc.

Environment

• Network: Arc Testnet (Chain ID 5042002)
• RPC: https://rpc.testnet.arc.network
• viem v2.48.11
• Observed: May 2025

Impact

Any DApp that submits ERC-20 transactions without an explicit gas price premium will silently fail. The error message does not indicate that the solution is a gas price bump — it looks like a nonce/mempool collision.

Suggested fix

The node should either (a) honor MetaMask/viem default gas price estimates without rejection, or (b) document that a minimum gas price premium is required for all Arc Testnet transactions.

[osr21]

Confirmed workaround + ethers.js v6 snippet

The +30% gas price bump is required specifically when transactions follow each other in quick
succession (e.g., the approve → burn sequence in a CCTP bridge flow). A standalone transaction
with the default gas price succeeds fine.

Ethers.js v6 pattern:

async function getGasOverrides(provider: ethers.Provider) {
  const feeData = await provider.getFeeData();
  // Apply 30% premium to avoid "replacement transaction underpriced" on rapid sequences
  const gasPrice = feeData.gasPrice != null
    ? (feeData.gasPrice * 130n) / 100n
    : undefined;
  return { gasPrice, gasLimit: 600_000n };
}

// Usage:
const overrides = await getGasOverrides(provider);
const tx1 = await usdc.approve(spender, amount, overrides);
await tx1.wait();
// overrides are already elevated — re-use or re-fetch for the next tx
const tx2 = await contract.nextMethod(args, overrides);

viem pattern (as described in the original report):

import { parseGwei } from "viem";
const gasPrice = await publicClient.getGasPrice();
const bumpedGasPrice = (gasPrice * 130n) / 100n;
const hash = await walletClient.writeContract({
  ...contract,
  gas: 600_000n,
  gasPrice: bumpedGasPrice,
});