من المستند إلى التنفيذ: مصفوفة التتبع

const express = require('express');const app = express();app.use(express.json()); const tokens = { 'tok-1': 1, 'tok-2': 2, 'tok-3': 3, 'tok-4': 4 };const course = { id: 1, title: 'تصميم الويب', capacity: 2, enrolled: [], waitlist: [] }; function auth(req, res, next) {  req.userId = tokens[(req.headers.authorization || '').replace('Bearer ', '')];  if (!req.userId) return res.status(401).json({ error: 'سجّل الدخول' });  next();} app.get('/api/courses/1', (req, res) => {  res.json({ enrolled: course.enrolled, waitlist: course.waitlist });}); // FR-02.2 + FR-15.1 + BR-06app.post('/api/courses/1/enroll', auth, (req, res) => {  if (course.enrolled.includes(req.userId) || course.waitlist.includes(req.userId))    return res.status(409).json({ error: 'مسجل أو منتظر مسبقًا' });            // BR-06  if (course.enrolled.length >= course.capacity) {                              // FR-15.1    course.waitlist.push(req.userId);    return res.status(202).json({ status: 'waitlisted', position: course.waitlist.length });  }  course.enrolled.push(req.userId);  res.status(201).json({ status: 'enrolled' });}); // FR-02.5 + FR-15.2app.delete('/api/courses/1/enroll', auth, (req, res) => {  course.enrolled = course.enrolled.filter(id => id !== req.userId);  let promoted = null;  if (course.enrolled.length < course.capacity && course.waitlist.length) {    promoted = course.waitlist.shift();    course.enrolled.push(promoted);  }  res.json({ cancelled: true, promoted });}); app.listen(3000);