Screen backdrop (schema v5/v6) + five-scene catalog + webcam polish: live desktop/game capture as a permanent non-deletable bottom layer (Source.IsBackdrop), auto full-screen game detection (Win32FullScreenDetector) else primary display, GraphicsCapturePicker re-designation, refcounted shared ScreenCaptureManager, Live-only backdrop by policy (HasBackdrop + v5-v6 backfill + EnforceBackdropPolicy, checkbox gone), SceneCatalog (Starting/Live/BRB/Chat/Ending) with + button re-adding missing scenes, webcam mid-session transparent-container fix (GetPreviewBitmap propagation), Chat half-screen-area cap, 'Add Webcam' always opens the picker (SwapWebcamIdentityAsync, no silent resurrect), WindowsRuntimeMarshal frame-read + 5s-throttled errors, docs updated, tests (65 passing)

MainWindow.xaml.cs

@@ -46,6 +46,16 @@ public partial class MainWindow : Window
         _viewModel.Shutdown();
     }
 
+    private void MainWindow_Activated(object? sender, EventArgs e)
+    {
+        _viewModel.RefreshBackdropAutoCapture();
+    }
+
+    private void MainWindow_Deactivated(object? sender, EventArgs e)
+    {
+        _viewModel.NoteBackgroundWindow();
+    }
+
     private void UpdateTaskbarOverlay()
     {
         TaskbarInfo.Overlay = _viewModel.IsLive
@@ -91,6 +101,16 @@ public partial class MainWindow : Window
         }
     }
 
+    private void AddSceneButton_Click(object sender, RoutedEventArgs e)
+    {
+        if (sender is Button { ContextMenu: { } menu } button)
+        {
+            menu.PlacementTarget = button;
+            menu.Placement = System.Windows.Controls.Primitives.PlacementMode.Bottom;
+            menu.IsOpen = true;
+        }
+    }
+
     // ─── Preview image selection / move / resize ───
     private bool _isDraggingOverlay;
     private bool _isResizing;
@@ -166,6 +186,22 @@ public partial class MainWindow : Window
             _viewModel.RemoveSourceCommand.Execute(element);
     }
 
+    private void BackdropMenu_ChangeCapture(object sender, RoutedEventArgs e)
+    {
+        _ = _viewModel.ChangeBackdropCaptureAsync();
+    }
+
+    private void BackdropMenu_RefreshCapture(object sender, RoutedEventArgs e)
+    {
+        _viewModel.RefreshBackdropAutoCapture();
+    }
+
+    private void SourceMenu_Remove(object sender, RoutedEventArgs e)
+    {
+        if (sender is MenuItem { DataContext: SceneElement element })
+            _viewModel.RemoveSourceCommand.Execute(element);
+    }
+
     private void OpacitySlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
         => OpacityValueText.Text = $"{Math.Round(e.NewValue * 100)}%";
 
@@ -227,8 +263,8 @@ public partial class MainWindow : Window
         else if (_isResizing)
         {
             var isWebcam = selected is WebcamSceneConfig;
-            var maxW = isWebcam ? MainViewModel.WebcamMaxWidth : 1920;
-            var maxH = isWebcam ? MainViewModel.WebcamMaxHeight : 1080;
+            var maxW = isWebcam ? MainViewModel.MaxWebcamWidthFor(_viewModel.ActiveScene?.Name) : 1920;
+            var maxH = isWebcam ? MainViewModel.MaxWebcamHeightFor(_viewModel.ActiveScene?.Name) : 1080;
             var newW = Math.Clamp(p.X - selected.X, 32, maxW);
             var newH = newW / _resizeAspect;
             if (newH > maxH)