Watch a URL for 1 hour: signed callbacks when its verdict changes

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0x38287535a4f47f53360940cfad8bf9ac5bc04a69",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "50000",
    "maxTimeoutSeconds": 300
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "body": {
          "callback_url": "https://agent.example/hooks/watch",
          "payload": {
            "deploy": "v2.3.1"
          },
          "url": "https://example.com"
        },
        "bodyType": "json",
        "method": "POST",
        "type": "http"
      },
      "output": {
        "example": {
          "expires_at": "2026-09-10T16:00:00+00:00",
          "interval_seconds": 300,
          "kind": "watch",
          "receipt": {
            "algorithm": "ed25519",
            "key_id": "…",
            "receipt_id": "01J…",
            "signature": "…"
          },
          "state": "active",
          "url": "https://example.com",
          "wake_id": "wk_01j…"
        },
        "type": "json"
      }
    },
    "schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "properties": {
        "input": {
          "additionalProperties": false,
          "properties": {
            "body": {
              "properties": {
                "callback_url": {
                  "description": "Public https URL that receives the POSTs. Private and reserved addresses are refused; redirects are not followed.",
                  "type": "string"
                },
                "payload": {
                  "description": "Up to 4 KB of JSON echoed back in every callback.",
                  "type": "object"
                },
                "url": {
                  "description": "The http(s) URL to watch. Public hosts only.",
                  "type": "string"
                }
              },
              "required": [
                "url",
                "callback_url"
              ]
            },
            "bodyType": {
              "enum": [
                "json",
                "form-data",
                "text"
              ],
              "type": "string"
            },
            "method": {
              "enum": [
                "POST"
              ],
              "type": "string"
            },
            "type": {
              "const": "http",
              "type": "string"
            }
          },
          "required": [
            "type",
            "method",
            "bodyType",
            "body"
          ],
          "type": "object"
        },
        "output": {
          "properties": {
            "example": {
              "type": "object"
            },
            "type": {
              "type": "string"
            }
          },
          "required": [
            "type"
          ],
          "type": "object"
        }
      },
      "required": [
        "input"
      ],
      "type": "object"
    }
  }
}

curl "https://sentinel.rootstuff.io/x402/watch-1h"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://sentinel.rootstuff.io/x402/watch-1h");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}

import httpx
res = httpx.get("https://sentinel.rootstuff.io/x402/watch-1h")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header