populated sub-documents have same references about mongoose HOT 1 CLOSED

const mongoose = require('mongoose');

// MongoDB connection URL
const MONGO_URI = 'mongodb://localhost:27017/mongoose_repro';

// Placeholder function to simulate URL signing
async function signUrl(avatarUrl) {
  // Simulate signing process
  return `${avatarUrl}?signed=true`;
}

const userSchema = new mongoose.Schema({
  username: String,
  avatar: String,
});

const messageSchema = new mongoose.Schema({
  chat: mongoose.Schema.Types.ObjectId,
  sender: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
  text: String,
  createdAt: { type: Date, default: Date.now },
});

const User = mongoose.model('User', userSchema);
const Message = mongoose.model('Message', messageSchema);

async function main() {
  await mongoose.connect(MONGO_URI);
  console.log('Connected to MongoDB');

  await User.deleteMany({});
  await Message.deleteMany({});

  // Create sample users and messages
  const user1 = new User({ username: 'user1', avatar: 'avatar1.png' });
  const user2 = new User({ username: 'user2', avatar: 'avatar2.png' });
  await user1.save();
  await user2.save();

  const chatId = new mongoose.Types.ObjectId();
  const messages = [
    new Message({ chat: chatId, sender: user1._id, text: 'Hello from user1' }),
    new Message({ chat: chatId, sender: user1._id, text: 'Another message from user1' }),
    new Message({ chat: chatId, sender: user2._id, text: 'Hello from user2' }),
  ];
  await Message.insertMany(messages);

  // Query and populate
  const populatedMessages = await Message.find({ chat: chatId })
    .sort({ createdAt: 1 })
    .populate('sender')
    .exec();

  // Attempt to sign avatars
  for (let message of populatedMessages) {
    message.sender.avatar = await signUrl(message.sender.avatar);
  }

  console.log('Populated Messages:', populatedMessages);

  // Clean up
  await mongoose.connection.close();
}

main().catch(err => console.error(err));

  // Query and populate
  const populatedMessages = await Message.find({ chat: chatId })
    .sort({ createdAt: 1 })
    .populate({ path: 'sender', clone: true }) // <-- add `clone: true` to make Mongoose clone result documents and avoid multiple messages having the same `sender`
    .exec();