Wallet

The Gully Game SDK never holds a private key. Every write to Gully Chain (submitting a score, completing a quest, paying an x402 invoice) goes through one interface, ITransactionSender, that you implement with whatever account the player uses.

#The seam

namespace GullyLabs.GameSdk
{
    public sealed class TransactionRequest
    {
        public string To;
        public string Data = "0x";
        public BigInteger Value = BigInteger.Zero;
        public long ChainId = GullyChain.TestnetChainId; // 485590
    }

    public interface ITransactionSender
    {
        string Address { get; }
        Task<string> SendTransactionAsync(TransactionRequest tx); // returns the tx hash once broadcast
    }
}

SDK methods that write take an ITransactionSender argument, for example GullyArcadeClient.SubmitScoreAsync(attestation, sender) and X402Client.GetAsync(url, sender). Methods that only build calldata (Erc20.TransferCalldata, Abi.Call) let you send it yourself.

#Which account backs it

The player's address comes from the Gully ID gully_account claim (see Gully ID).

#Session keys

A passkey cannot sign silently mid-game. Instead, at sign-in the player approves a session key: a short-lived key, held by the game client, that the smart account accepts only for the calls and limits you request (for example: only submitScore on GullyArcade and complete on QuestRegistry, for 24 hours, with no value transfers). If the device is lost, the session expires on its own.

#Sponsored gas

Gully accounts on Gully Chain have gas sponsored through the ERC-4337 paymaster, so players do not need ETH to play. The sender builds a user operation for the smart account and sends it to the Gully Chain bundler; the paymaster pays the fee.

#A minimal sender for testing

For editor tests against a local chain or a throwaway testnet key, a sender can sign raw transactions and post them with JsonRpcClient.SendRawTransactionAsync. Keep such keys out of the repo and out of builds.

public sealed class DevSender : ITransactionSender
{
    readonly JsonRpcClient _rpc;
    readonly IMyTestSigner _signer;               // your own signing code, editor-only
    public DevSender(JsonRpcClient rpc, IMyTestSigner signer) { _rpc = rpc; _signer = signer; }
    public string Address => _signer.Address;
    public async Task<string> SendTransactionAsync(TransactionRequest tx)
    {
        string raw = await _signer.SignAsync(tx); // signed, RLP-encoded transaction hex
        return await _rpc.SendRawTransactionAsync(raw);
    }
}

#Rules

• Request the narrowest session permissions that work, and the shortest lifetime.
• Show the player what a transaction does before the first approval.
• Link to the explorer after a write: GullyChain.TxUrl(txHash).