Добавьте файлы проекта.

src/Massenger.Client/Pages/ChatPage.xaml.cs

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+using Massenger.Client.Services;
+using Massenger.Client.ViewModels;
+
+namespace Massenger.Client.Pages;
+
+[QueryProperty(nameof(ChatId), "chatId")]
+public partial class ChatPage : ContentPage
+{
+    private readonly ChatViewModel _viewModel;
+
+    private string? _chatId;
+
+    public string? ChatId
+    {
+        get => _chatId;
+        set
+        {
+            _chatId = value;
+            _ = LoadChatAsync(value);
+        }
+    }
+
+    public ChatPage()
+    {
+        InitializeComponent();
+        _viewModel = ServiceHelper.GetRequiredService<ChatViewModel>();
+        _viewModel.AttachRealtime();
+        BindingContext = _viewModel;
+    }
+
+    protected override void OnDisappearing()
+    {
+        base.OnDisappearing();
+        _viewModel.DetachRealtime();
+    }
+
+    private async Task LoadChatAsync(string? chatId)
+    {
+        if (Guid.TryParse(chatId, out var parsed))
+        {
+            await _viewModel.LoadAsync(parsed);
+        }
+    }
+}