Self-Custody Signing Reference

{
  stepId: string;        // send it back verbatim
  type: SignatureRequestType;
  venue: string;         // who the request is for; switch on `type`, not this
  signerAddress: string; // the wallet that must sign or send
  chainId?: number;      // often absent; read the chain from the payload
  payload: unknown;      // sign or send it verbatim
  expiresAt: string;     // ISO-8601; always read it
  purpose?: string;      // for display: funding, funding_and_fee, fee, app_fee, referral_payout
}

import { serializeSignature } from "viem";
import type { SignerFn } from "@agg-build/sdk";

const mySigner: SignerFn = async (req) => {
  switch (req.type) {
    case "eip712":
    case "hl_l1_action":
      return walletClient.signTypedData(req.payload as never);

    case "personal_sign": {
      const p = req.payload as string | { raw: `0x${string}` };
      return walletClient.signMessage({ message: typeof p === "string" ? p : { raw: p.raw } });
    }

    case "safe_tx": {
      const { safeTxHash } = req.payload as { safeTxHash: `0x${string}` };
      return walletClient.signMessage({ message: { raw: safeTxHash } });
    }

    case "eip7702_authorization": {
      const auth = await walletClient.signAuthorization(req.payload as never);
      // viem types `yParity` and `v` as optional. Derive rather than default:
      // a wrong parity recovers to another address and the server rejects it.
      const yParity = auth.yParity ?? (auth.v === undefined ? undefined : Number(auth.v) - 27);
      if (yParity !== 0 && yParity !== 1) throw new Error("authorization has no usable parity");
      return serializeSignature({ r: auth.r, s: auth.s, yParity });
    }

    case "transaction": {
      const tx = req.payload as { chainId: string; to: string; value: string; data: string };
      // Broadcast on the request's chain, not whichever one the wallet is on.
      await walletClient.switchChain({ id: Number(tx.chainId) });
      // Return the hash right away. Do NOT wait for the receipt.
      return {
        txHash: await walletClient.sendTransaction({
          to: tx.to as `0x${string}`,
          value: BigInt(tx.value), // decimal wei string; "0" for an approve
          data: tx.data as `0x${string}`,
        }),
      };
    }

    default:
      throw new Error(`unsupported signature request: ${req.type}`);
  }
};