从零重建 Q2 · 并发任务调度器Rebuild Q2 · the concurrent task runner
空文件夹。实现一个带并发上限的异步任务调度器：并发数不得超过上限、结果顺序与输入一致、失败的任务以 rejected 出现而不是让整批崩掉。An empty folder. Implement an async task scheduler with a concurrency limit: never run more than the limit at once, keep results in input order, and report a failed task as rejected instead of letting the whole batch fail.
题面在下一页。计时基准是「开考那一刻」的时间戳，存在本机 —— 刷新、切标签页、关掉浏览器再回来都不会重置，也不会把你踢回这一屏。The paper is on the next page. The clock is anchored to the timestamp taken when you start and lives in this browser: refreshing, switching tabs or closing the window and coming back will not reset it, and will not throw you back to this screen.
所以别用它当预览 —— 想先看题的话，那已经不是考场了。So do not use it as a preview. If you look at the paper first, this stops being an exam.
- 从空文件夹开始。自己 npm init、自己装依赖、自己配脚本。脚手架是考试内容的一部分。Start from an empty folder. Run npm init yourself, install deps yourself, wire the scripts yourself.
- 计时期间不许打开对应的课、练习场、模拟考讲解。提示和参考答案要交卷才解锁。While the clock runs, no lessons, no practice page, no walkthroughs. Hints and the reference answer unlock only after you hand in.
- 查官方文档、查报错、查 API 签名都允许 —— 真实考试也允许。抄这个站里的答案不允许。Official docs, error messages and API signatures are fair game, same as the real assessment. Copying this site's answers is not.
- 时限到了不会强制打断。计时器变红，交卷记录里标「超时」—— 什么时候停由你决定，但记录如实。Hitting the limit does not stop you. The clock turns red and the attempt is tagged over-time. You decide when to stop, the record stays honest.
- 交卷后先逐条勾验收命令的真实结果，再看提示和答案。顺序不能反。After handing in, tick the real result of each acceptance command first. Hints and answers come after that, not before.
- 中途放弃也会记一条「放弃」，而且抹不掉。记录难看才有约束力。Giving up records a gave-up attempt, and it stays. A record you can quietly delete constrains nobody.
它是源项目里那道题的「从零重写」版：不给脚手架、不给起始代码，只给需求和验收命令。参考答案就是源项目里的真实实现。It is the from-scratch version of a task in the source project: no scaffold, no starter code, only requirements and acceptance commands. The reference answer is the real implementation from that project.
还没准备好？先回去过一遍Not ready yet? Go back through React CapstoneReact Capstone。考场里没有提示按钮，卡住了只能靠已经会的东西。. There is no hint button in here; if you get stuck, you get stuck with what you already know.
正在读本机记录…Reading local records…
题目：从零重建 Q2 · 并发任务调度器。记录只存在这台浏览器里，换设备看不到。Challenge: 从零重建 Q2 · 并发任务调度器. Records live in this browser only.