[Python] ExactEvmScheme silently accepts raw LocalAccount but fails at sign time

[endcycles]

Bug

ExactEvmScheme(signer=account) accepts an eth_account.signers.local.LocalAccount without error, but fails later during create_payment_payload with a confusing ValueError from encode_typed_data.

The issue is that LocalAccount.sign_typed_data has a different signature than the ClientEvmSigner protocol:

# ClientEvmSigner protocol (what ExactEvmScheme calls):
sign_typed_data(domain, types, primary_type, message) -> bytes

# LocalAccount.sign_typed_data (what gets called):
sign_typed_data(domain_data=None, message_types=None, message_data=None, full_message=None)

When called positionally, primary_type (a string) lands in the message_data parameter, and message (a dict) lands in full_message. This triggers:

ValueError: You may supply either `full_message` as a single argument or
`domain_data`, `message_types`, and `message_data` as three arguments, but not both.

Steps to Reproduce

from eth_account import Account
from x402 import PaymentRequired, x402ClientSync
from x402.mechanisms.evm.exact import ExactEvmScheme

account = Account.from_key("0x...")

# This is accepted without error but will fail later:
scheme = ExactEvmScheme(signer=account)

client = x402ClientSync()
client.register("eip155:*", scheme)

# Fails here with ValueError from encode_typed_data
payload = client.create_payment_payload(payment_required)

Workaround

Wrap the account in EthAccountSigner:

from x402.mechanisms.evm.signers import EthAccountSigner

signer = EthAccountSigner(account)
scheme = ExactEvmScheme(signer=signer)

Suggestion

Either:

1. Add a type check / runtime validation in ExactEvmScheme.__init__ that rejects LocalAccount with a helpful error pointing to EthAccountSigner
2. Auto-wrap LocalAccount instances in EthAccountSigner when detected
3. Document the requirement prominently in the README

Environment

• x402 Python SDK v2.0.0
• eth-account 0.13.7
• Python 3.12

[madisoncarter1234]

took a swing at both of your issues, let me know if this works!