REELCAST · x402

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Build "REELCAST" in ONE Lovable message. Single-page x402-native paid app on Sei Devnet (arctic-1).

CONCEPT
A pay-per-view casting vault where actors pay to pin their career to IPFS and casting directors pay to unlock high-res reels. No subscriptions, just 0.01 USDC to view a performance or drop a digital headshot into a production folder. Facilitator handles the EIP-3009 signature, ensuring actors are compensated for 'audition data' and agents pay for access.
Discipline: Theater & Live Performance (performance showcase).
Onchain primitive: x402 micropayments on Sei Devnet arctic-1 (USDC via EIP-3009). Why: Legacy casting platforms lock talent behind monthly fees; this meters the interaction. By treating every click on a reel as a transaction, it filter-proofs the talent pool and creates a micro-economy for talent scouts.

5-CREDIT BUDGET (HARD LIMIT):
- ONE single-page app. No Lovable Cloud, no database, no auth flows beyond Privy drop-in.
- NO smart contract deploy. x402 settles USDC via EIP-3009 `transferWithAuthorization` — the USDC contract already exists at 0x4E4a29F76Cd0dff2A4e5e56D7A065E0aF33f32e2 on Sei Devnet arctic-1 (chainId 713715).
- Privy is the auth + signing layer (Google login + embedded wallet).
- At most ONE AI call per user action (Lovable AI Gateway with LOVABLE_API_KEY, only if AI is part of the idea).
- Skip tests, skip CI, skip docs. Ship the demo.

CHAIN CHOICE (non-obvious — read before you swap chains)
PayAI's x402 facilitator settles Sei traffic ONLY on Sei Devnet arctic-1 (chainId 713715, deprecated per chainid.network but live at facilitator). It does NOT settle on Sei Testnet atlantic-2 (chainId 1328). Do not swap for atlantic-2 — the EIP-712 domain will mismatch and PayAI returns `invalid_signature`.

STACK
- React + Vite + TanStack Start (the template Lovable ships).
- viem does NOT export arctic-1. Define it once in src/lib/sei-arctic.ts:
    import { defineChain } from "viem";
    export const seiArctic = defineChain({
      id: 713715, name: "Sei Devnet (arctic-1)",
      nativeCurrency: { name: "Sei", symbol: "SEI", decimals: 18 },
      rpcUrls: { default: { http: ["https://evm-rpc-arctic-1.sei-apis.com"] } },
      blockExplorers: { default: { name: "Seiscan", url: "https://testnet.seiscan.io" } },
      testnet: true,
    });
- Privy embedded wallet, lazy + client-only mount (`@privy-io/react-auth` crashes under SSR):
    import { seiArctic } from "@/lib/sei-arctic";
    <PrivyProvider appId={import.meta.env.VITE_PRIVY_APP_ID}
      config={{ loginMethods:['google'],
                embeddedWallets:{ ethereum:{ createOnLogin:'users-without-wallets' } },
                defaultChain: seiArctic as never,
                supportedChains: [seiArctic] as never }}>
- viem public client uses the arctic-1 RPC — put it in src/data/rpc.json as
  { "seiArctic": "https://evm-rpc-arctic-1.sei-apis.com" } and use
  createPublicClient({ chain: seiArctic, transport: http(rpc.seiArctic) }).

TEN NON-OBVIOUS x402 RULES (get these wrong and it silently fails)
1. CORS: proxy the facilitator. Public x402 facilitators (including x402.payai.network) do NOT send
   Access-Control-Allow-Origin. A direct browser fetch throws "TypeError: Failed to fetch" BEFORE
   you see the 402. Wrap the upstream call in a same-origin TanStack server route at
   src/routes/api/public/x402-proxy.ts and forward PAYMENT-SIGNATURE (request) + PAYMENT-RESPONSE (response).
2. x402 v2 envelope shape. The base64-encoded PAYMENT-SIGNATURE payload is NOT
   { scheme, network, payload } at top level — that's v1 and PayAI rejects it as invalid_payload.
   It MUST be:
     { "x402Version": 2,
       "accepted": { /* the full PaymentRequirement you picked, echoed back verbatim */ },
       "payload":  { "signature": "0x…",
                     "authorization": { from, to, value, validAfter, validBefore, nonce } } }
3. Network id is CAIP-2: "eip155:713715" for Sei Devnet arctic-1 (NOT "sei-testnet" and NOT "eip155:1328").
   Match on this when picking a requirement from accepts[].
4. Amount field renamed. v2 uses `amount` (atomic units, string), NOT v1's `maxAmountRequired`.
   USDC has 6 decimals — "10000" = 0.01 USDC.
5. Header names are literal-cased and non-standard: PAYMENT-SIGNATURE (request) and PAYMENT-RESPONSE (response).
6. EIP-3009 domain fields come from requirement.extra. Use extra.name ("USDC") and extra.version ("2")
   in the EIP-712 domain — NOT hardcoded. chainId is 713715; verifyingContract is requirement.asset.
7. nonce is bytes32 random, generated client-side (crypto.getRandomValues(new Uint8Array(32)) → 0x-hex).
   Never reuse. validAfter = now-60s, validBefore = now + maxTimeoutSeconds (default 300).
8. Sign via Privy embedded wallet's provider, NOT React hooks: get the EIP-1193 provider
   (const provider = await embedded.getEthereumProvider()) and call
   provider.request({ method: "eth_signTypedData_v4", params: [address, JSON.stringify(typedData)] }).
9. Use the arctic-1 RPC from src/data/rpc.json (rule above). USDC balanceOf against a random public RPC will flake.
10. Fund flow: NO public USDC faucet on arctic-1. Show the user's Privy address prominently,
    link them to arctic-1 SEI faucet (https://sei-faucet.nima.enterprises) for gas (not actually
    required — x402 is gasless — but reassuring), and add a UI note asking to DM PayAI / a
    maintainer for 0.10 arctic-1 USDC. Then a "Refresh balance" button.

FILE LAYOUT
  src/data/x402.json          { endpoint, proxy, usdcAddress: "0x4E4a29F76Cd0dff2A4e5e56D7A065E0aF33f32e2",
                                chainId: 713715, network: "eip155:713715",
                                faucetUrl: "https://sei-faucet.nima.enterprises",
                                explorer: "https://testnet.seiscan.io" }
  src/data/rpc.json           { "seiArctic": "https://evm-rpc-arctic-1.sei-apis.com" }
  src/lib/sei-arctic.ts       defineChain wrapper (viem has no arctic-1 export)
  src/lib/x402.ts             fetchChallenge / pickRequirement / signPayment / fetchPaid
  src/routes/api/public/x402-proxy.ts   same-origin GET proxy (below)
  src/routes/index.tsx        demo UI: sign-in → fund → 4-step flow log

PROXY ROUTE (drop-in — copy verbatim):
```ts
// src/routes/api/public/x402-proxy.ts
import { createFileRoute } from "@tanstack/react-router";
import x402Cfg from "@/data/x402.json";

export const Route = createFileRoute("/api/public/x402-proxy")({
  server: {
    handlers: {
      GET: async ({ request }) => {
        const sig = request.headers.get("PAYMENT-SIGNATURE");
        const upstream = await fetch(x402Cfg.endpoint, {
          method: "GET",
          headers: sig ? { "PAYMENT-SIGNATURE": sig } : {},
        });
        const body = await upstream.arrayBuffer();
        const out = new Headers();
        const ct = upstream.headers.get("content-type");
        if (ct) out.set("Content-Type", ct);
        const pr = upstream.headers.get("PAYMENT-RESPONSE");
        if (pr) out.set("PAYMENT-RESPONSE", pr);
        return new Response(body, { status: upstream.status, headers: out });
      },
    },
  },
});
```

The /api/public/* prefix bypasses Lovable's published-site auth — desired for a demo endpoint.

USER FLOW (log every step in the UI so the user sees what happened)
1. Land on page → "Sign in with Google" (Privy) → embedded wallet auto-provisioned on Sei Devnet arctic-1.
2. Fund: show wallet address + "Get 0.01 USDC on Sei arctic-1" → link to PayAI Discord / maintainer for USDC
   → "Refresh balance" button reads USDC balanceOf via viem + the arctic-1 RPC.
3. Click the primary action button for this idea (performance showcase). App runs:
   (a) Challenge — GET /api/public/x402-proxy → expect 402 → parse { x402Version:2, accepts:[…], error }.
       Pick accepts[] where network === "eip155:713715" && scheme === "exact".
   (b) Sign — Build EIP-3009 typed data (see rules 6–8), call Privy signTypedData,
       wrap into the v2 envelope (rule 2), base64.
   (c) Retry — GET /api/public/x402-proxy with header PAYMENT-SIGNATURE: <base64>.
   (d) Settle — On 200, read PAYMENT-RESPONSE header, base64-decode →
       { success, transaction, network, payer }. Link tx to `${explorer}/tx/${transaction}`.
4. Footer renders: "Built during the Creative AI & Quantum Hackathon organised by StreetKode Fam during Indian Krump Festival 14"

FACILITATOR
Default endpoint: https://x402.payai.network/api/sei-testnet/paid-content (returns 402 with an
accepts[] challenge, settles 0.01 USDC per successful call on Sei Devnet arctic-1, returns the
protected payload). Note: PayAI's path is called "sei-testnet" but the underlying chain is
arctic-1 (chainId 713715), not atlantic-2 (chainId 1328).

REQUIRED SECRETS (Lovable → Project Settings → Secrets):
- PRIVY_APP_ID          Google sign-in + embedded wallet. In the Privy dashboard, add Sei Devnet
                        (713715, RPC https://evm-rpc-arctic-1.sei-apis.com). No Gas Sponsorship
                        policy needed (x402 is gasless). Docs: https://docs.privy.io/llms-full.txt

COMMON FAILURE MODES (fix these before shipping)
- "TypeError: Failed to fetch" at step (a): called the facilitator directly from the browser. Use the proxy.
- "invalid_payload" at step (c): sent v1 envelope. Wrap under `accepted` (rule 2).
- "invalid_signature": wrong domain — chainId mismatch (must be 713715, not 1328), or extra.version
  hardcoded to "1". Use chainId 713715 and extra.version from the requirement.
- "insufficient_funds": wallet has SEI but no USDC. Request arctic-1 USDC from PayAI / maintainer,
  then Refresh balance.
- Balance stays at 0 after funding: reading against the wrong RPC. Point at
  https://evm-rpc-arctic-1.sei-apis.com via rpc.json (NOT the atlantic-2 RPC).
- expires_at errors on retry: clock skew or reused nonce. Generate fresh nonce + timestamps per attempt.

CREDIT (must appear in UI footer):
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.