Transactions 与消费顺序 — Downcity Payments

Topup 和 Charge 都产生一条 CreditsTransaction。每张受影响 Card 对应一条不可变 CreditsTransactionEntry，Entry 同时承担账本职责。

await bureau.credits.charge({
  user_id: "user_123",
  credits: 250_000,
  source: "model_usage",
  ref: "request_456",
  idempotency_key: "model_usage:request_456",
});

未指定 Card 时，服务按到期时间从早到晚消费有效 Ephemeral Cards，再消费 Primary Card。指定 Card 时不会跨 Card。总额度不足时整体失败并返回 402，不会产生部分扣费。

const transactions = await bureau.credits.transactions.list({ user_id: "user_123" });
const entries = await bureau.credits.history.list({ transaction_id: transactions[0].transaction_id });