[BUG] Rabby agent approval fails because EIP-712 chainId is hard-coded to 421614

Update after further debugging

I have some additional findings after investigating both the frontend and backend.

1. Rabby is working correctly

The wallet is connected correctly.

window.ethereum.isRabby
// true

window.ethereum.chainId
// "0xa4b1"

window.ethereum.selectedAddress
// 0xe1...

The wallet is on Arbitrum One (42161).

2. The frontend signs using a hard-coded chain

Intercepting the EIP-712 request shows NOFX builds the typed-data with:

{
  "domain": {
    "chainId": 421614
  },
  "message": {
    "signatureChainId": "0x66eee",
    "hyperliquidChain": "Mainnet"
  }
}

Rabby rejects this because the connected wallet is on Arbitrum One (42161).

3. After patching the wallet request

I monkey-patched the frontend so that the wallet signs using:

domain.chainId = 42161
signatureChainId = 0xa4b1

This allows Rabby to display the signing popup.

So the original issue is definitely caused by the frontend constructing the EIP-712 payload with a hard-coded chain.

4. The backend rejects the patched request

Once the wallet signs successfully, the request reaches the backend.

Instead of succeeding, the backend returns:

POST /api/hyperliquid/submit-exchange

400 Bad Request

{
  "error": "invalid signatureChainId"
}

Looking through the repository shows why.

The backend explicitly validates:

if strings.TrimSpace(fmt.Sprint(action["signatureChainId"])) != "0x66eee" {
    return fmt.Errorf("invalid signatureChainId")
}

The frontend also hard-codes:

signatureChainId: "0x66eee"

in multiple places.

5. This creates a compatibility deadlock

Current behavior:

• Wallet on Arbitrum One → Rabby refuses to sign because the typed-data uses 421614.
• Patch frontend to use the wallet chain → backend rejects the request because it only accepts 0x66eee.

So both the frontend and backend currently assume a fixed signature chain.

6. I don't believe this is a wallet issue

The wallet is functioning normally.

The problem appears to be that NOFX assumes:

signatureChainId = 0x66eee

everywhere.

This works only if every wallet accepts signing for that domain.

Rabby follows EIP-712 more strictly and requires the signing domain to match the active chain.

Suggested fix

The frontend should obtain the connected wallet chain dynamically:

const chainId = await provider.request({
    method: "eth_chainId",
});

and sign using that chain.

The backend should validate that the signature is valid rather than requiring:

signatureChainId == "0x66eee"

This would make Hyperliquid onboarding compatible with Rabby and other EIP-1193 wallets while preserving Hyperliquid Mainnet operation.