Reliability: ETH/USD price with retry-with-backoff and last-known-good cache fallback laye

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0xf74f2020aC3d73F2Bf5ee0F8Bf635475eA881319",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "10000",
    "maxTimeoutSeconds": 300
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "method": "GET",
        "queryParams": {
          "simulateFailureRate": 0
        },
        "type": "http"
      },
      "output": {
        "example": {
          "attempts": 0,
          "cacheAgeSeconds": 0,
          "ethUsdPrice": 0,
          "simulateFailureRate": 0,
          "source": "live"
        },
        "type": "json"
      }
    },
    "schema": {
      "properties": {
        "input": {
          "properties": {
            "queryParams": {
              "properties": {
                "simulateFailureRate": {
                  "description": "0-1, simulates upstream failures to demo the fallback path.",
                  "type": "number"
                }
              },
              "required": [],
              "type": "object"
            }
          }
        },
        "output": {
          "properties": {
            "example": {
              "properties": {
                "attempts": {
                  "type": "integer"
                },
                "cacheAgeSeconds": {
                  "type": [
                    "number",
                    "null"
                  ]
                },
                "ethUsdPrice": {
                  "type": "number"
                },
                "simulateFailureRate": {
                  "type": "number"
                },
                "source": {
                  "enum": [
                    "live",
                    "cache-fallback"
                  ],
                  "type": "string"
                }
              },
              "type": "object"
            }
          }
        }
      }
    }
  }
}

curl "https://lab.paidapis.net/api/reliable-eth-price"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://lab.paidapis.net/api/reliable-eth-price");
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://lab.paidapis.net/api/reliable-eth-price")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header