const res = await fetch(url, { method: "POST", headers, body });
const reader = res.body!.getReader();
const decoder = new TextDecoder();
let buffer = "";
let text = "";

while (true) {
  const { done, value } = await reader.read();
  if (done) break;
  buffer += decoder.decode(value, { stream: true });

  const lines = buffer.split("\n");
  buffer = lines.pop() ?? "";

  for (const line of lines) {
    if (!line.startsWith("data: ")) continue;

    const payload = line.slice(6);
    if (payload === "[DONE]") return text;   // 必须先判断，否则 JSON.parse 抛错

    const evt = JSON.parse(payload);
    switch (evt.type) {
      case "output.text.delta":
        text += evt.delta ?? evt.content ?? "";
        break;
      case "usage.trial_exhausted":
        showPurchasePrompt();               // 不要落进错误分支
        break;
      case "run.failed":
        throw new Error(evt.message ?? "run failed");
      default:
        if (evt.type?.startsWith("tool_call.")) renderToolCall(evt);
    }
  }
}

import json

async for line in response.aiter_lines():
    if not line.startswith("data: "):
        continue

    payload = line[6:]
    if payload == "[DONE]":
        break

    evt = json.loads(payload)
    t = evt.get("type")

    if t == "output.text.delta":
        print(evt.get("delta") or evt.get("content") or "", end="", flush=True)
    elif t == "usage.trial_exhausted":
        handle_trial_exhausted()
    elif t == "run.failed":
        raise RuntimeError(evt.get("message", "run failed"))