Gasless XR Art Swap

Required keys.

Add these in your Lovable project under Settings → Secrets before pasting the prompt below.

Paste into a fresh Lovable project. Make sure all five secrets above are set first. read the build strategy →

Build "Gasless XR Art Swap" in ONE Lovable message. Single-page demo.

CONCEPT
Trade XR art pieces effortlessly with embedded wallets and sponsored transactions.
Discipline: Game Design & Interactive Media (interactive art exchange).
Onchain primitive: Privy social + sponsored tx. Why this primitive: Privy embedded wallet with Linea Sepolia tx removes gas friction in art trades.

5-CREDIT BUDGET (HARD LIMIT):
- ONE single-page app. No router, no Lovable Cloud, no database, no auth flows beyond Privy drop-in.
- ONE Solidity contract, <=80 lines, deployed to Linea Sepolia, verified on LineaScan.
- Privy is always the auth layer (Google login, embedded wallet). Users pay their own gas — Linea Sepolia gas is negligible (sub-cent), so no paymaster or sponsorship is needed.
- Pinata/IPFS only if the idea genuinely needs to store a file or metadata.
- At most ONE AI call per user action (use Lovable AI Gateway with LOVABLE_API_KEY if AI is part of the idea).
- Skip tests, skip CI, skip docs pages. Ship the demo, nothing else.

STACK
- React + Vite single page (the index route).
- SSR-safe Privy mount is mandatory. Never import @privy-io/react-auth at
  module scope of a route file — it crashes SSR. Use
  lazy(() => import('./privy-client-entry')) inside <ClientOnly> + <Suspense>,
  and put <PrivyProvider> only inside privy-client-entry.tsx.
- PrivyProvider config MUST declare Linea Sepolia as the default AND only
  supported chain — otherwise Privy defaults to Ethereum mainnet, refuses
  switchChain(59141) silently, and sendTransaction hangs forever with the
  button stuck on "Logging on chain…". Import lineaSepolia from viem/chains:
    import { lineaSepolia } from 'viem/chains';
    <PrivyProvider appId={import.meta.env.VITE_PRIVY_APP_ID}
      config={{ loginMethods:['google','email'],
                embeddedWallets:{ ethereum:{ createOnLogin:'users-without-wallets' } },
                appearance:{ theme:'dark' },
                defaultChain: lineaSepolia,
                supportedChains: [lineaSepolia] }}>
- Read the embedded wallet from useWallets, not user.wallet:
    const embedded = wallets.find(w => w.walletClientType === 'privy');
- Before every send, make sure the wallet is on Linea Sepolia:
    if (embedded.chainId !== 'eip155:59141') await embedded.switchChain(59141);
- Send with chainId per-call. Users approve each tx and pay their own gas —
  Linea Sepolia gas is negligible (sub-cent), so no sponsorship is needed:
    await sendTransaction(
      { to, data, chainId: 59141 },
      { address: embedded.address }
    );
- Do NOT pass `sponsor: true`, ZeroDev, SmartWalletsProvider, or a paymaster URL.
  This app runs on Linea Sepolia; users pay the tiny gas themselves.
- Hardhat in /contracts (kept outside the Vite bundle). Install
  `@nomicfoundation/hardhat-toolbox` AND `@nomicfoundation/hardhat-verify@latest`
  (>=3.x — older versions still hit Etherscan v1 and fail with
  "You are using a deprecated V1 endpoint, switch to Etherscan API V2").
- hardhat.config.cjs uses the Etherscan v2 shape with a customChains entry
  for Linea Sepolia (LineaScan is on Etherscan Multichain — same API key):
    require("@nomicfoundation/hardhat-toolbox");
    require("@nomicfoundation/hardhat-verify");
    module.exports = {
      solidity: { version: "0.8.24", settings: { optimizer: { enabled: true, runs: 200 } } },
      networks: { linea_sepolia: {
        url: process.env.LINEA_SEPOLIA_RPC_URL,                 // Alchemy Linea Sepolia HTTPS URL, REQUIRED
        accounts: [process.env.METAMASK_PRIVATE_KEY.startsWith("0x")
          ? process.env.METAMASK_PRIVATE_KEY : "0x" + process.env.METAMASK_PRIVATE_KEY],
        chainId: 59141,
      } },
      etherscan: {
        apiKey: { linea_sepolia: process.env.ETHERSCAN_API_KEY },
        customChains: [{
          network: "linea_sepolia",
          chainId: 59141,
          urls: {
            apiURL: "https://api-sepolia.lineascan.build/api",
            browserURL: "https://sepolia.lineascan.build",
          },
        }],
      },
      sourcify: { enabled: false },
    };
- Deploy: `npx hardhat run scripts/deploy.cjs --network linea_sepolia`.
- Verify (run RIGHT AFTER deploy, no constructor args for these contracts):
  `npx hardhat verify --network linea_sepolia <address>`
  On success LineaScan returns "Successfully verified contract … on the block explorer"
  and the source becomes readable at
  `https://sepolia.lineascan.build/address/<address>#code`.
- Frontend reads: create a viem public client with the Alchemy URL —
  `createPublicClient({ chain: lineaSepolia, transport: http(import.meta.env.VITE_LINEA_SEPOLIA_RPC_URL) })`
  (import `lineaSepolia` from `viem/chains`). Expose the RPC to the client by
  also setting VITE_LINEA_SEPOLIA_RPC_URL to the same value.
- Write the deployed address to `src/data/contract.json` so the UI links to
  `https://sepolia.lineascan.build/address/<address>`.

CONTRACT (contracts/GaslessXRArtSwap.sol):
```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;
/// @title SocialLogGaslessXRArtSwap
/// @notice Trade XR art pieces effortlessly with embedded wallets and sponsored transactions.
/// @notice Built during the Creative AI & Quantum Hackathon organised by StreetKode Fam during Indian Krump Festival 14
contract SocialLogGaslessXRArtSwap {
    event Logged(address indexed author, string cid, uint256 at);
    /// @notice Built during the Creative AI & Quantum Hackathon organised by StreetKode Fam during Indian Krump Festival 14
    function log(string calldata cid) external {
        emit Logged(msg.sender, cid, block.timestamp);
    }
}
```

USER FLOW
1. Land on page -> 'Sign in with Google' (Privy) -> embedded wallet auto-provisioned.
2. Every interactive art exchange action the user performs is sent as a Linea Sepolia tx (`log(payload)`) via the Privy embedded wallet, and displayed with a LineaScan link.
3. Footer renders: "Built during the Creative AI & Quantum Hackathon organised by StreetKode Fam during Indian Krump Festival 14"

REQUIRED SECRETS (Lovable -> Project Settings -> Secrets):
- METAMASK_PRIVATE_KEY   Linea Sepolia deployer key. Fund it: https://www.hackquest.io/faucets/59141
- LINEA_SEPOLIA_RPC_URL  Alchemy Linea Sepolia HTTPS endpoint (https://linea-sepolia.g.alchemy.com/v2/<key>). Create a free app at https://dashboard.alchemy.com/ -> copy the HTTPS URL. Public RPCs throttle under hackathon load — Alchemy is required.
- ETHERSCAN_API_KEY      For `npx hardhat verify` — LineaScan is on Etherscan Multichain, so the same key works. Get: https://etherscan.io/myapikey
- PRIVY_APP_ID           Google sign-in + embedded wallet. Docs: https://docs.privy.io/llms-full.txt
- PINATA_JWT             IPFS uploads (only if app pins media). Docs: https://docs.pinata.cloud/llms-full.txt

CREDIT (must appear in UI footer AND as NatSpec on every deployed contract):
Built during the Creative AI & Quantum Hackathon organised by StreetKode Fam during Indian Krump Festival 14

Market sizing.

Indicative figures for hackathon pitches — refine with your own research before raising.