Return bounded factual eth_estimateGas units and recent eth_feeHistory execution-fee evide

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0xdb7b2b54f80479826222749a2ea73a8acc306e1e",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "5000",
    "maxTimeoutSeconds": 60
  }
]

{
  "bazaar": {
    "info": {
      "description": "Return bounded factual eth_estimateGas units and recent eth_feeHistory execution-fee evidence for one unsigned Ethereum or Base transaction. Not execution, signing, custody, trading, or a guaranteed final cost. Call when you need point-in-time gas units and recent execution-fee context before signing or submitting.",
      "input": {
        "body": {
          "chain": "eip155:8453",
          "data": "0x",
          "to": "0x0000000000000000000000000000000000000001",
          "value_wei": "0"
        },
        "bodyType": "json",
        "method": "POST",
        "type": "http"
      },
      "output": {
        "example": {
          "chain": {
            "caip2": "eip155:8453",
            "chain_id": 8453,
            "name": "base"
          },
          "fee_history": {
            "block_count": 5,
            "newest_block": "latest"
          },
          "gas_estimate": {
            "gas_units": "21000"
          },
          "illustrative_execution_fees": {
            "covers": "l2_execution_fee_only",
            "guaranteed_final_cost": false,
            "kind": "illustrative_execution_fee_observations",
            "recommendation": false
          },
          "limitations": [
            "Point-in-time gas evidence, not a guaranteed final cost or total transaction cost."
          ],
          "machine": "VM06",
          "methodology_version": "transaction-gas-preflight-0.1.0",
          "request_shape": {
            "calldata_bytes": 0,
            "has_from": false,
            "value_nonzero": false
          },
          "status": "OK"
        },
        "type": "json"
      }
    },
    "schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "properties": {
        "input": {
          "additionalProperties": false,
          "properties": {
            "body": {
              "additionalProperties": false,
              "properties": {
                "chain": {
                  "description": "Analysis chain only. Payment remains Base eip155:8453.",
                  "enum": [
                    "eip155:1",
                    "eip155:8453"
                  ],
                  "type": "string"
                },
                "data": {
                  "description": "Optional 0x-prefixed even-length hex calldata. Default 0x. Maximum 8192 bytes. Request body maximum 20480 bytes.",
                  "maxLength": 16386,
                  "pattern": "^0x(?:[0-9a-fA-F]{2})*$",
                  "type": "string"
                },
                "from": {
                  "description": "Optional 0x-prefixed 20-byte sender used only as an eth_estimateGas field. No ownership is implied.",
                  "pattern": "^0x[0-9a-fA-F]{40}$",
                  "type": "string"
                },
                "to": {
                  "description": "Required 0x-prefixed 20-byte destination. Contract creation is not supported.",
                  "pattern": "^0x[0-9a-fA-F]{40}$",
                  "type": "string"
                },
                "value_wei": {
                  "description": "Optional unsigned base-10 integer string in the uint256 range. Default 0. JSON Schema cannot express the full uint256 upper bound; runtime validation rejects values above 2^256-1.",
                  "pattern": "^(0|[1-9][0-9]*)$",
                  "type": "string"
                }
              },
              "required": [
                "chain",
                "to"
              ],
              "type": "object"
            },
            "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": {
              "additionalProperties": true,
              "properties": {
                "chain": {
                  "type": "object"
                },
                "fee_history": {
                  "description": "Recent eth_feeHistory execution-fee evidence.",
                  "type": [
                    "object",
                    "null"
                  ]
                },
                "gas_estimate": {
                  "description": "eth_estimateGas units when estimable.",
                  "type": [
                    "object",
                    "null"
                  ]
                },
                "illustrative_execution_fees": {
                  "description": "Illustrative L2 execution-fee observations, not a guaranteed final cost.",
                  "type": [
                    "object",
                    "null"
                  ]
                },
                "limitations": {
                  "items": {
                    "type": "string"
                  },
                  "type": "array"
                },
                "machine": {
                  "enum": [
                    "VM06"
                  ],
                  "type": "string"
                },
                "methodology_version": {
                  "enum": [
                    "transaction-gas-preflight-0.1.0"
                  ],
                  "type": "string"
                },
                "request_shape": {
                  "type": "object"
                },
                "status": {
                  "enum": [
                    "OK",
                    "PARTIAL",
                    "UNESTIMABLE",
                    "HOLD"
                  ],
                  "type": "string"
                }
              },
              "required": [
                "status",
                "machine",
                "methodology_version",
                "chain",
                "gas_estimate",
                "limitations"
              ],
              "type": "object"
            },
            "type": {
              "type": "string"
            }
          },
          "required": [
            "type"
          ],
          "type": "object"
        }
      },
      "required": [
        "input"
      ],
      "type": "object"
    }
  }
}

curl "https://api.agentmercantile.com/v1/transaction-gas-preflight"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://api.agentmercantile.com/v1/transaction-gas-preflight");
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://api.agentmercantile.com/v1/transaction-gas-preflight")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header