[bug] WalletConnectConnector.getChainId() returns CAIP-2 string, breaks wagmi writeContract

[okwme]

Description

WalletConnectConnector.getChainId() returns the CAIP-2 network ID (e.g., "eip155:84532") instead of a numeric chain ID. This causes viem's writeContract to fail with:

Cannot convert eip155:84532 to a BigInt

The AuthConnector correctly wraps this with a parseChainId() helper that extracts the numeric portion, but WalletConnectConnector does not.

Steps to Reproduce

1. Use @reown/appkit-adapter-wagmi v1.8.18+ with wagmi v3
2. Connect via WalletConnect (or AppKit's embedded wallet)
3. Call writeContract from @wagmi/core (or useWriteContract from @wagmi/vue / wagmi)
4. The call fails with Cannot convert eip155:84532 to a BigInt

Root Cause

In WalletConnectConnector (source):

async getChainId() {
  const chainId = ChainController.getActiveCaipNetwork(ConstantsUtil.CHAIN.EVM)?.id;
  // ❌ Returns CAIP network ID like "eip155:84532" directly
  return chainId;
}

In AuthConnector, this is handled correctly:

function parseChainId(chainId) {
  let network = Number(NetworkUtil.parseEvmChainId(chainId));
  // ✅ Extracts numeric chain ID
}

async getChainId() {
  const { chainId } = await provider.getChainId();
  return parseChainId(chainId);  // ✅ Returns numeric
}

wagmi's writeContract internally calls getConnectorClient() which calls connector.getChainId(). The CAIP-2 string is passed to viem, which tries BigInt("eip155:84532") and throws.

Workaround

We bypass wagmi's writeContract entirely by encoding calldata manually and using viem's sendTransaction with chain: null:

import { encodeFunctionData } from 'viem'
import { sendTransaction } from 'viem/actions'
import { getConnectorClient } from '@wagmi/core'

async function writeContract(config, params) {
  const client = await getConnectorClient(config, { chainId })
  const data = encodeFunctionData({
    abi: params.abi,
    functionName: params.functionName,
    args: params.args,
  })
  return sendTransaction(client, {
    to: params.address,
    data,
    chain: null, // Skip chain validation
  })
}

Note: even with getConnectorClient returning a client with the correct numeric chain.id, viem's writeContract still fails because it re-queries the chain from the connector internally.

Expected Fix

WalletConnectConnector.getChainId() should parse the CAIP network ID to extract the numeric chain ID, similar to how AuthConnector does it:

async getChainId() {
  const caipNetworkId = ChainController.getActiveCaipNetwork(ConstantsUtil.CHAIN.EVM)?.id;
  if (caipNetworkId) {
    const parts = String(caipNetworkId).split(':');
    return Number(parts[parts.length - 1]);
  }
  // fallback...
}

Environment

• @reown/appkit: 1.8.18
• @reown/appkit-adapter-wagmi: 1.8.18
• @wagmi/core: 3.4.0
• @wagmi/vue: 0.1.11
• viem: 2.46.3
• Chain: Base Sepolia (84532)
• Wallet: AppKit embedded wallet via WalletConnect

[linear]

REOWN-4533