Web source: off-screen WebView2 capture + layout persistence + transparent bg

Bundle exception (2026-08-27): this lands prior-session work plus today's
transparency fix as one commit per creator instruction.

WebView2Manager (new): off-screen WebView2 control parked at -5000/-5000 in
the window's visual tree, captures via CapturePreviewAsync every 100 ms into
a BGRA8 VideoFrame. Source Width/Height sync to the control via
PropertyChanged. JS transparent-background injection runs on every
NavigationStarting/NavigationCompleted so the page's own CSS does not paint
white over the capture.

Transparency fix: DefaultBackgroundColor = System.Drawing.Color.Transparent
set on the WPF control before EnsureCoreWebView2Async. The WPF SDK doc says
the value is forwarded to the controller on init; the IDL (ICoreWebView2-
Controller2) confirms alpha=0 makes the capture alpha-preserving. The
prior-session 'CoreWebView2.BackgroundColor' path was the wrong property
name and has been replaced.

LayoutStore: WebUri column added (idempotent ALTER TABLE) and round-tripped
on save/load (schema v11).

MainViewModel: WebView2Manager constructed on Loaded; loaded web sources
re-registered; Source.WebUri PropertyChanged forwards to manager.

MainWindow: off-screen host Canvas added to visual tree.

Tests: 3 scale-sync + WebView2_DefaultBackgroundColor_Is_Transparent +
LayoutStorePersistenceTests.WebSource_WebUri_Persists. 234/236 pass
(2 pre-existing failures unchanged).

Scale bug (DPI/physical-pixel mismatch) still open.

ViewModels/MainViewModel.cs

@@ -131,6 +131,7 @@ public class MainViewModel : ViewModelBase
     private readonly ScreenCaptureManager _screenCaptureManager;
     private readonly ScreenCaptureSourceFactory _screenCaptureFactory;
     private readonly ChatBoxRenderer _chatBoxRenderer;
+    private WebView2Manager? _webView2Manager;
 
     // Mock chat messages for the ChatBox preview — branded placeholders so the
     // creator sees where the overlay lands before going live.
@@ -1892,6 +1893,7 @@ public class MainViewModel : ViewModelBase
         UpdateBackgroundImage();
         ReacquireWebcam();
         ReacquireScreenCaptures();
+        RegisterLoadedWebSources();
         _socials = _layoutStore.Socials;
         RenderSocialBarFrame();
         HealFediverseSoftwareInBackground();
@@ -2109,6 +2111,22 @@ public class MainViewModel : ViewModelBase
         _fullScreenDetector.StartWatching();
     }
 
+    private void RegisterLoadedWebSources()
+    {
+        if (_webView2Manager == null) return;
+
+        foreach (var source in Scenes.SelectMany(s => s.Elements).OfType<Source>()
+                     .Where(s => s.Type == SourceType.WebSource))
+        {
+            _webView2Manager.Register(source);
+            source.PropertyChanged += (_, e) =>
+            {
+                if (e.PropertyName == nameof(Source.WebUri))
+                    _webView2Manager.OnWebUriChanged(source);
+            };
+        }
+    }
+
     // ScreenCaptureManager creates the shared WriteableBitmap on the UI thread;
     // every background pointing at that key picks it up.
     private void OnScreenPreviewBitmapChanged(string key, WriteableBitmap bitmap)
@@ -2272,6 +2290,19 @@ public class MainViewModel : ViewModelBase
         _ = RedesignateBackgroundAsync($"{MonitorKeyPrefix}{display.Index}");
     }
 
+    public void InitWebView2(Panel hostPanel)
+    {
+        _webView2Manager = new WebView2Manager(hostPanel, System.Windows.Application.Current.Dispatcher);
+        _webView2Manager.PreviewBitmapChanged += OnWebView2PreviewBitmapChanged;
+    }
+
+    private void OnWebView2PreviewBitmapChanged(string sourceId, WriteableBitmap bitmap)
+    {
+        foreach (var scene in Scenes)
+            foreach (var el in scene.Elements.OfType<Source>().Where(s => s.Id == sourceId))
+                el.VideoImageSource = bitmap;
+    }
+
     public void Shutdown()
     {
         _saveDebounce?.Stop();
@@ -2280,6 +2311,7 @@ public class MainViewModel : ViewModelBase
         _framePump.Dispose();
         _cameraManager.Dispose();
         _screenCaptureManager.Dispose();
+        _webView2Manager?.Dispose();
         _layoutStore.Dispose();
         _musicPlayer.Dispose();
         _youtubeChat.Dispose();
@@ -2488,7 +2520,7 @@ public class MainViewModel : ViewModelBase
             SourceType.Image => "Image",
             SourceType.TextOverlay => "Text",
             SourceType.Countdown => "Countdown",
-            SourceType.WebSource => "Web",
+            SourceType.WebSource => "Web Resource",
             SourceType.ChatBox => "YouTube Chat",
             _ => "Layer",
         };
@@ -2501,17 +2533,31 @@ public class MainViewModel : ViewModelBase
         if (sourceType == SourceType.ChatBox && !CanAddYouTubeChat)
             return;
 
+        // Web resources use "Web Resource-N" naming (0-indexed per scene)
+        var webCount = scene.Elements.OfType<Source>().Count(s => s.Type == SourceType.WebSource);
         var source = new Source
         {
-            Name = NextSourceName(scene, baseName),
+            Name = sourceType == SourceType.WebSource
+                ? $"{baseName}-{webCount}"
+                : NextSourceName(scene, baseName),
             Type = sourceType,
             X = sourceType == SourceType.ChatBox ? 1400 : 0,
             Y = sourceType == SourceType.ChatBox ? 20 : 0,
-            Width = sourceType == SourceType.ChatBox ? 500 : 0,
-            Height = sourceType == SourceType.ChatBox ? 648 : 0,
+            Width = sourceType == SourceType.WebSource ? 640 : sourceType == SourceType.ChatBox ? 500 : 0,
+            Height = sourceType == SourceType.WebSource ? 480 : sourceType == SourceType.ChatBox ? 648 : 0,
         };
         scene.Elements.Add(source);
 
+        if (sourceType == SourceType.WebSource)
+        {
+            _webView2Manager?.Register(source);
+            source.PropertyChanged += (_, e) =>
+            {
+                if (e.PropertyName == nameof(Source.WebUri))
+                    _webView2Manager?.OnWebUriChanged(source);
+            };
+        }
+
         if (sourceType == SourceType.ChatBox)
         {
             source.PropertyChanged += (_, e) =>
@@ -2797,6 +2843,8 @@ public class MainViewModel : ViewModelBase
                 SelectedElement = null;
             _ = _cameraManager.ReleaseAsync(_webcam.DeviceId);
         }
+        if (element is Source { Type: SourceType.WebSource } webSource)
+            _webView2Manager?.Unregister(webSource.Id);
         scene.Elements.Remove(element);
 
         if (element is WebcamSceneConfig && _webcam != null
@@ -3200,6 +3248,7 @@ public class MainViewModel : ViewModelBase
             WebcamSceneConfig webcam => _cameraManager.GetLatestFrame(webcam.WebcamId),
             Source { IsLiveCapture: true, CaptureKey: not null } live => _screenCaptureManager.GetLatestFrame(live.CaptureKey),
             Source { Type: SourceType.ChatBox } chatBox => RenderChatBox(chatBox),
+            Source { Type: SourceType.WebSource } web => _webView2Manager?.GetLatestFrame(web.Id),
             Source { AssetId: not null } image => StaticPixelCache.Get(image.AssetId),
             _ => null,
         };