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)

Models/Source.cs

@@ -27,7 +27,22 @@ public enum ClipShape
 public class Source : SceneElement
 {
     private SourceType _type;
-    public SourceType Type { get => _type; set => Set(ref _type, value); }
+    public SourceType Type
+    {
+        get => _type;
+        set
+        {
+            if (Set(ref _type, value))
+            {
+                Raise(nameof(IsLiveCapture));
+                Raise(nameof(DisplaySource));
+            }
+        }
+    }
+
+    /// <summary>The permanent scene backdrop (live desktop/game capture). Never removable/reorderable.</summary>
+    private bool _isBackdrop;
+    public bool IsBackdrop { get => _isBackdrop; set => Set(ref _isBackdrop, value); }
 
     private bool _isEnabled = true;
     public bool IsEnabled { get => _isEnabled; set => Set(ref _isEnabled, value); }
@@ -39,6 +54,15 @@ public class Source : SceneElement
     private IntPtr? _windowHandle;
     public IntPtr? WindowHandle { get => _windowHandle; set => Set(ref _windowHandle, value); }
 
+    /// <summary>
+    /// Identifies what this live-capture source points at: "monitor:&lt;index&gt;" or
+    /// "window:&lt;hwnd&gt;". Persisted so a re-designated backdrop survives a reload.
+    /// </summary>
+    private string? _captureKey;
+    public string? CaptureKey { get => _captureKey; set => Set(ref _captureKey, value); }
+
+    public bool IsLiveCapture => Type is SourceType.DisplayCapture or SourceType.WindowCapture;
+
     // Image (asset stored in the layout database)
     private string? _assetId;
     private ImageSource? _imageSource;
@@ -59,7 +83,7 @@ public class Source : SceneElement
 
     public ImageSource? ImageSource => _imageSource;
 
-    public override ImageSource? DisplaySource => _imageSource;
+    public override ImageSource? DisplaySource => IsLiveCapture ? VideoImageSource : _imageSource;
 
     public override bool IsImageSource => Type == SourceType.Image;
 }