Align 402 response field names with x402 V2 spec

[andreabadesso]

Current behavior

Our 402 response uses some field names that differ from the x402 V2 spec:

{
  "accepts": [{
    "scheme": "hathor-escrow",
    "network": "hathor:testnet",
    "asset": "00",
    "amount": "100",
    "description": "Pay 1.00 HTR",
    "payTo": "WZe3ty22...",
    "maxTimeoutSeconds": 300,
    "extra": {
      "facilitatorUrl": "https://facilitator.x402.hathor.dev",
      "facilitatorAddress": "Wb6eLTZS...",
      "blueprintId": "0000121e...",
      "deadlineSeconds": 300
    }
  }]
}

x402 V2 spec field names

The V2 spec uses these field names in the accepts array entries:

• scheme ✅ (matches)
• network ✅ (matches)
• asset ✅ (matches)
• price — we use amount. The spec calls it price.
• payTo ✅ (matches)
• description ✅ (matches)
• resource ✅ (matches)
• mimeType ✅ (matches)

The extra field is Hathor-specific (escrow blueprint ID, facilitator address, deadline). The spec doesn't define this — each scheme can add its own fields.

Changes needed

Resource server (resource-server.js)

• Rename amount to price in the 402 response
• Keep amount in the facilitator verify/settle payloads (internal, not spec-facing)

Client (client.js) and dApp (dapp/components/X402Fetch.tsx)

• Read price instead of amount from 402 responses

Facilitator (facilitator.js)

• Accept both maxAmountRequired and price in verify requests for compatibility

References

• x402 V2 seller quickstart
• The V2 route config uses { scheme, price, network, payTo }