API 契約

以下保留檔案原文，沒有改寫資料或結果。可使用「複製原始內容」取得完整檔案。

{
  "kind": "teaching-contract-not-openapi",
  "version": "demo-api-1",
  "endpoint": "POST /payments",
  "request": {"order_id": "non-empty string"},
  "responses": {
    "200": {"order_id": "requested order", "status": "PAID"},
    "400": {"error": "INVALID_REQUEST"},
    "404": {"error": "ORDER_NOT_FOUND"},
    "409": {"error": "ORDER_ALREADY_PAID"}
  },
  "persistence": {
    "orders": "id TEXT PRIMARY KEY, status TEXT NOT NULL (PENDING or PAID)",
    "payments": "id INTEGER PRIMARY KEY, order_id TEXT NOT NULL",
    "successful_payment": "one payment row and PENDING -> PAID in one atomic transaction",
    "rejected_payment": "no state or row count changes",
    "concurrency": "two simultaneous requests for one PENDING order yield one 200, one 409 and one payment"
  },
  "not_in_scope": ["real payment provider", "authentication", "pricing", "refunds", "multi-tenant isolation"]
}