Escape hatch for power users: forward an arbitrary read-only JSON-RPC method to the chain. Method must be in our read-only whitelist (eth_call, eth_getLogs, eth_getBlockByNumber, eth_getTransactionReceipt, eth_chainId, eth_blockNumber, etc.). Mutating methods (eth_sendTransaction, eth_sendRawTransaction) are rejected — sign and broadcast through your own provider.