Construyendo Comercio Agéntico #4: Pagos Stablecoin x402 — Cuando los Agentes Pagan en USDC

POST /api/v1/agent/checkout HTTP/1.1
Host: api.agenticmcpstores.com
Content-Type: application/json
PAYMENT-SIGNATURE: eyJzaWduYXR1cmUiOiIweGFiYy4uLiIsImF1dGhvcml6YXRpb24iOnsiZnJvbSI6IjB4MTExMSIsInRvIjoiMHgyMjIyIiwidmFsdWUiOiI1MDAwMDAwIiwidmFsaWRBZnRlciI6IjE3MTI1MDAwMDAiLCJ2YWxpZEJlZm9yZSI6IjE3MTI1MDM2MDAiLCJub25jZSI6IjB4ZGVhZGJlZWYifSwic2NoZW1lIjoiZXhhY3QiLCJuZXR3b3JrIjoiYmFzZSJ9

{"items": [{"productId": "prod_001", "quantity": 1}]}

HTTP/1.1 402 Payment Required
PAYMENT-REQUIRED: eyJzY2hlbWUiOiJleGFjdCIsIm5ldHdvcmsiOiJiYXNlIi4uLn0=

{
  "paymentRequired": {
    "scheme": "exact",
    "network": "base",
    "maxAmountRequired": "5000000",
    "payTo": "0x2222...merchant_wallet",
    "maxTimeoutSeconds": 1800,
    "extra": {
      "tokenAddress": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "name": "USDC",
      "version": "2"
    }
  },
  "facilitator": {
    "verifyUrl": "https://x402.org/facilitator/verify",
    "settleUrl": "https://x402.org/facilitator/settle"
  }
}

// Payload PAYMENT-SIGNATURE V2 (decodificado de base64)
{
  "signature": "0xabc123...firma_eip712",
  "authorization": {
    "from": "0x1111...wallet_agente",
    "to": "0x2222...wallet_merchant",
    "value": "5000000",
    "validAfter": "1712500000",
    "validBefore": "1712503600",
    "nonce": "0xdeadbeef"
  },
  "scheme": "exact",
  "network": "base"
}

// Lógica de reintento de liquidación (simplificada)
for (let attempt = 0; attempt < 5; attempt++) {
  if (attempt > 0) {
    await sleep(5000 * Math.pow(2, attempt - 1)); // 5s, 10s, 20s, 40s
  }
  const result = await fetch(facilitator.settleUrl, {
    method: "POST",
    body: JSON.stringify({ paymentPayload, paymentRequired }),
    signal: AbortSignal.timeout(15_000) // 15s timeout por solicitud
  });
  if (result.success) {
    return { status: "COMPLETED", txHash: result.txHash };
  }
}
return { status: "FAILED" };

// Inbound: unidades mínimas USDC → centavos USD
// 1 USDC (1,000,000 unidades) = 100 centavos → dividir por 10,000
const cents = parseInt(usdcSmallestUnit) / 10_000;
// Ejemplo: "5000000" (5 USDC) → 500 centavos ($5.00)

// Outbound: centavos USD → unidades mínimas USDC
const usdc = String(Math.round(cents * 10_000));
// Ejemplo: 500 centavos → "5000000" (5 USDC)

// Almacenado en MerchantProtocol.config (base de datos)
{
  "protocol": "X402",
  "enabled": true,
  "priority": 100,
  "config": {
    "walletAddress": "0xAbCd...wallet_merchant",
    "network": "base",
    "facilitatorUrl": "https://x402.org/facilitator",
    "supportedTokens": ["USDC"],
    "maxTransactionAmount": 100000000  // 100 USDC límite de seguridad
  }
}

┌──────────┐     verify      ┌──────────────────────┐
│  PENDING │ ──────────────→ │ x402_pending_payment  │
└──────────┘                 └──────────┬───────────┘
                                        │
                          ┌─────────────┼─────────────┐
                          ↓             ↓             ↓
                    ┌───────────┐ ┌───────────┐ ┌─────────┐
                    │ completed │ │ x402_failed│ │ expired │
                    └───────────┘ └───────────┘ └─────────┘

Estados terminales no pueden sobreescribirse.
Expiración: job cada 30 minutos captura pagos atascados.