refactor: extract ChatOverlayLayer — real component decomposition, Commit G

The first true decomposition of the 4105-line god-object, not another partial
shuffle. MainViewModel.Chat.cs 194 -> 44 lines of thin delegation; all chat
behavior now lives in a self-contained Services/ChatOverlayLayer.cs (199):

- Owns the message buffer (Messages), ChatBoxRenderer, fade + mock-preview
  timers, per-source preview renders, and the live-output RenderFrame path.
- The VM keeps only the binding surface: ChatMessages delegates to
  _chatLayer.Messages (so XAML ItemsSource + LeftPanel CollectionChanged hold),
  CanAddYouTubeChat / ShowChatInactiveMessage stay computed on the VM
  (OnPropertyChanged raised from VM setters + XAML-bound), and thin forwards.
- Scenes handed in as args (no Func seam), so the layer owns no scene graph.

An AI reading ChatOverlayLayer.cs now sees the entire chat feature in one
self-contained unit. Zero behavior change; build 0 warnings; 246 pass, only the
2 known failures. Docs: ViewModels/index.md tracker updated in same commit.

Services/ChatOverlayLayer.cs

@@ -0,0 +1,199 @@
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Windows;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Threading;
+using ytLive.Helpers;
+using ytLive.Models;
+
+namespace ytLive.Services;
+
+/// <summary>Owns the YouTube-chat overlay behavior: the message buffer, the
+/// renderer, and the fade/mock-preview timers. The MainViewModel keeps only the
+/// thin binding surface (the shared <see cref="Messages"/> collection + two
+/// computed gate props) and hands the scene list in at each call — this class
+/// owns all chat logic so an AI can read one self-contained unit.</summary>
+public sealed class ChatOverlayLayer
+{
+    private readonly ChatBoxRenderer _renderer;
+
+    // Mock chat messages for the ChatBox preview — branded placeholders so the
+    // creator sees where the overlay lands before going live.
+    private static readonly IReadOnlyList<ChatMessage> MockChatMessages = new[]
+    {
+        new ChatMessage { AuthorName = "LlamaCasty", Message = "welcome to the stream!", Timestamp = DateTime.Now.AddMinutes(-4), IsMember = true },
+        new ChatMessage { AuthorName = "LlamaCastyFan", Message = "$10 — LlamaCasty is the best!", Timestamp = DateTime.Now.AddMinutes(-3), IsSuperChat = true },
+        new ChatMessage { AuthorName = "GamerDude", Message = "what streaming software is this?", Timestamp = DateTime.Now.AddMinutes(-2) },
+        new ChatMessage { AuthorName = "LlamaCasty", Message = "thanks for watching! llamacasty.com", Timestamp = DateTime.Now.AddMinutes(-1), IsMember = true },
+        new ChatMessage { AuthorName = "LlamaDog", Message = "Subscribe so they can buy the subscription at llamacasty.com!", Timestamp = DateTime.Now, IsMember = true },
+    };
+
+    // Chat fade timer: clears chat overlay after N seconds of inactivity.
+    private DispatcherTimer? _fadeTimer;
+    private CancellationTokenSource? _mockCts;
+
+    /// <summary>The live chat message buffer. Shared with the ViewModel (which
+    /// binds it to the panel) via <c>ChatMessages =&gt; _chatLayer.Messages</c>.</summary>
+    public ObservableCollection<ChatMessage> Messages { get; } = new();
+
+    public ChatOverlayLayer(ChatBoxRenderer renderer) => _renderer = renderer;
+
+    /// <summary>Ingest a message from the poller. UI-thread marshalled: appended
+    /// to the buffer (capped at 500), mock preview stopped, swipe to real
+    /// messages, and the fade timer reset. Scenes are handed in so the layer can
+    /// refresh every ChatBox preview without owning the scene graph.</summary>
+    public void OnMessageReceived(ChatMessage message, IEnumerable<Scene> scenes)
+    {
+        System.Windows.Application.Current.Dispatcher.Invoke(() =>
+        {
+            Messages.Add(message);
+            if (Messages.Count > 500)
+                Messages.RemoveAt(0);
+
+            // Reset chat fade timer on every message
+            ResetChatFadeTimer(scenes);
+
+            StopMockPreview();
+
+            // Switch ChatBox previews from mock to real messages
+            foreach (var chatBox in scenes.SelectMany(s => s.Elements).OfType<Source>()
+                         .Where(s => s.Type == SourceType.ChatBox))
+                UpdatePreview(chatBox);
+        });
+    }
+
+    private void ResetChatFadeTimer(IEnumerable<Scene> scenes)
+    {
+        _fadeTimer?.Stop();
+        var chatBoxes = scenes.SelectMany(s => s.Elements).OfType<Source>()
+            .Where(s => s.Type == SourceType.ChatBox && s.ChatFadeSeconds > 0).ToList();
+        if (chatBoxes.Count == 0) return;
+
+        var delay = chatBoxes.Min(s => s.ChatFadeSeconds);
+        _fadeTimer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(delay) };
+        _fadeTimer.Tick += (_, _) =>
+        {
+            _fadeTimer?.Stop();
+            _fadeTimer = null;
+            Messages.Clear();
+            foreach (var chatBox in scenes.SelectMany(s => s.Elements).OfType<Source>()
+                         .Where(s => s.Type == SourceType.ChatBox))
+                UpdatePreview(chatBox);
+            StartMockPreview(scenes);
+        };
+        _fadeTimer.Start();
+    }
+
+    /// <summary>Renders the live-output frame for one ChatBox element (the
+    /// compositor path), or null when no messages are buffered yet. Mirrors the
+    /// preview render but without writing onto the source's VideoImageSource.</summary>
+    public VideoFrame? RenderFrame(Source chatBox)
+    {
+        if (Messages.Count == 0) return null;
+
+        var width = (int)Math.Max(1, chatBox.Width);
+        var height = (int)Math.Max(1, chatBox.Height);
+
+        return _renderer.Render(
+            Messages,
+            width,
+            height,
+            chatBox.ChatFontSize,
+            chatBox.ChatFontFamily,
+            chatBox.ChatFontColor,
+            chatBox.ChatBackgroundColor,
+            chatBox.ChatMaxMessages,
+            chatBox.ChatShowTimestamps,
+            chatBox.ChatShowBadges,
+            chatBox.ChatMemberColor,
+            chatBox.ChatSuperChatColor);
+    }
+
+    /// <summary>Renders one ChatBox preview: real messages when connected, mock
+    /// when not. Writes the resulting bitmap onto the source's
+    /// <c>VideoImageSource</c>.</summary>
+    public void UpdatePreview(Source chatBox, IReadOnlyList<ChatMessage>? messages = null)
+    {
+        try
+        {
+            messages ??= Messages.Count > 0 ? (IReadOnlyList<ChatMessage>)Messages : MockChatMessages;
+            var width = (int)Math.Max(32, chatBox.Width);
+            var height = (int)Math.Max(32, chatBox.Height);
+
+            var frame = _renderer.Render(
+                messages,
+                width,
+                height,
+                chatBox.ChatFontSize,
+                chatBox.ChatFontFamily,
+                chatBox.ChatFontColor,
+                chatBox.ChatBackgroundColor,
+                chatBox.ChatMaxMessages,
+                chatBox.ChatShowTimestamps,
+                chatBox.ChatShowBadges,
+                chatBox.ChatMemberColor,
+                chatBox.ChatSuperChatColor);
+
+            var bitmap = new WriteableBitmap(width, height, 96, 96, PixelFormats.Bgra32, null);
+            bitmap.WritePixels(new Int32Rect(0, 0, width, height), frame.BgraPixels, frame.Stride, 0);
+            chatBox.VideoImageSource = bitmap;
+        }
+        catch (Exception ex) { AppLog.Write($"UpdateChatBoxPreview failed: {ex.Message}"); }
+    }
+
+    private async Task RunMockPreviewAsync(Source chatBox, CancellationToken ct)
+    {
+        var n = 0;
+        while (!ct.IsCancellationRequested)
+        {
+            UpdatePreview(chatBox, MockChatMessages.Take(n + 1).ToList());
+            await Task.Delay(1000, ct);
+            n++;
+            if (n == MockChatMessages.Count)
+            {
+                await Task.Delay(3000, ct);
+                n = 0;
+            }
+        }
+    }
+
+    public void StartMockPreview(IEnumerable<Scene> scenes)
+    {
+        StopMockPreview();
+        _mockCts = new CancellationTokenSource();
+        var ct = _mockCts.Token;
+        foreach (var chatBox in scenes.SelectMany(s => s.Elements).OfType<Source>()
+                     .Where(s => s.Type == SourceType.ChatBox && s.ChatPreviewEnabled))
+            _ = RunMockPreviewAsync(chatBox, ct);
+    }
+
+    public void StopMockPreview()
+    {
+        _mockCts?.Cancel();
+        _mockCts?.Dispose();
+        _mockCts = null;
+    }
+
+    /// <summary>Render previews + wire property-change subscriptions for all
+    /// ChatBox sources across every scene. Called after layout load so existing
+    /// ChatBox sources show mock content and respond to config changes.</summary>
+    public void UpdateConfiguredBoxes(IEnumerable<Scene> scenes)
+    {
+        foreach (var scene in scenes)
+            foreach (var chatBox in scene.Elements.OfType<Source>().Where(s => s.Type == SourceType.ChatBox))
+            {
+                chatBox.PropertyChanged += (_, e) =>
+                {
+                    if (e.PropertyName is nameof(Source.ChatFontSize) or nameof(Source.ChatFontColor)
+                        or nameof(Source.ChatBackgroundColor) or nameof(Source.ChatBackgroundOpacity)
+                        or nameof(Source.ChatMaxMessages) or nameof(Source.ChatShowTimestamps)
+                        or nameof(Source.ChatShowBadges) or nameof(Source.ChatMemberColor)
+                        or nameof(Source.ChatSuperChatColor) or nameof(Source.ChatFontFamily)
+                        or nameof(Source.ChatFadeSeconds) or nameof(Source.Width) or nameof(Source.Height))
+                        UpdatePreview(chatBox);
+                };
+                UpdatePreview(chatBox);
+            }
+    }
+}

ViewModels/MainViewModel.Chat.cs

@@ -1,7 +1,5 @@
 using System.Collections.ObjectModel;
-using System.Windows.Media;
-using System.Windows.Media.Imaging;
-using System.Windows.Threading;
+using System.Linq;
 using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.Services;
@@ -11,22 +9,12 @@ namespace ytLive.ViewModels;
 public partial class MainViewModel : ViewModelBase
 {
 
-    private readonly ChatBoxRenderer _chatBoxRenderer;
+    private readonly ChatOverlayLayer _chatLayer;
 
-    // Mock chat messages for the ChatBox preview — branded placeholders so the
-    // creator sees where the overlay lands before going live.
-    private static readonly IReadOnlyList<ChatMessage> MockChatMessages = new[]
-    {
-        new ChatMessage { AuthorName = "LlamaCasty", Message = "welcome to the stream!", Timestamp = DateTime.Now.AddMinutes(-4), IsMember = true },
-        new ChatMessage { AuthorName = "LlamaCastyFan", Message = "$10 — LlamaCasty is the best!", Timestamp = DateTime.Now.AddMinutes(-3), IsSuperChat = true },
-        new ChatMessage { AuthorName = "GamerDude", Message = "what streaming software is this?", Timestamp = DateTime.Now.AddMinutes(-2) },
-        new ChatMessage { AuthorName = "LlamaCasty", Message = "thanks for watching! llamacasty.com", Timestamp = DateTime.Now.AddMinutes(-1), IsMember = true },
-        new ChatMessage { AuthorName = "LlamaDog", Message = "Subscribe so they can buy the subscription at llamacasty.com!", Timestamp = DateTime.Now, IsMember = true },
-    };
-    // Chat fade timer: clears chat overlay after N seconds of inactivity.
-    private System.Windows.Threading.DispatcherTimer? _chatFadeTimer;
-
-    public ObservableCollection<ChatMessage> ChatMessages { get; } = new();
+    /// <summary>The live chat message buffer — the same collection the
+    /// <see cref="ChatOverlayLayer"/> owns; here so XAML can bind it and the
+    /// left panel can subscribe to its changes.</summary>
+    public ObservableCollection<ChatMessage> ChatMessages => _chatLayer.Messages;
 
     /// <summary>The Add → YouTube Chat menu item: enabled only while no chat layer exists
     /// anywhere — one chat overlay per layout.</summary>
@@ -37,158 +25,20 @@ public partial class MainViewModel : ViewModelBase
     public bool ShowChatInactiveMessage => !IsLive;
 
     private void OnChatMessageReceived(ChatMessage message)
-    {
-        System.Windows.Application.Current.Dispatcher.Invoke(() =>
-        {
-            ChatMessages.Add(message);
-            if (ChatMessages.Count > 500)
-                ChatMessages.RemoveAt(0);
+        => _chatLayer.OnMessageReceived(message, Scenes);
 
-            // Reset chat fade timer on every message
-            ResetChatFadeTimer();
-
-            StopMockChatPreview();
-
-            // Switch ChatBox previews from mock to real messages
-            if (StagedScene != null)
-                foreach (var chatBox in StagedScene.Elements.OfType<Source>().Where(s => s.Type == SourceType.ChatBox))
-                    UpdateChatBoxPreview(chatBox);
-        });
-    }
-
-    private void ResetChatFadeTimer()
-    {
-        _chatFadeTimer?.Stop();
-        var chatBoxes = Scenes.SelectMany(s => s.Elements).OfType<Source>()
-            .Where(s => s.Type == SourceType.ChatBox && s.ChatFadeSeconds > 0).ToList();
-        if (chatBoxes.Count == 0) return;
-
-        var delay = chatBoxes.Min(s => s.ChatFadeSeconds);
-        _chatFadeTimer = new System.Windows.Threading.DispatcherTimer
-        { Interval = TimeSpan.FromSeconds(delay) };
-        _chatFadeTimer.Tick += (_, _) =>
-        {
-            _chatFadeTimer?.Stop();
-            _chatFadeTimer = null;
-            ChatMessages.Clear();
-            foreach (var chatBox in Scenes.SelectMany(s => s.Elements).OfType<Source>()
-                         .Where(s => s.Type == SourceType.ChatBox))
-                UpdateChatBoxPreview(chatBox);
-            StartMockChatPreview();
-        };
-        _chatFadeTimer.Start();
-    }
+    private void UpdateChatBoxPreview(Source chatBox, IReadOnlyList<ChatMessage>? messages = null)
+        => _chatLayer.UpdatePreview(chatBox, messages);
 
     private VideoFrame? RenderChatBox(Source chatBox)
-    {
-        if (ChatMessages.Count == 0) return null;
-
-        var width = (int)Math.Max(1, chatBox.Width);
-        var height = (int)Math.Max(1, chatBox.Height);
-
-        return _chatBoxRenderer.Render(
-            ChatMessages,
-            width,
-            height,
-            chatBox.ChatFontSize,
-            chatBox.ChatFontFamily,
-            chatBox.ChatFontColor,
-            chatBox.ChatBackgroundColor,
-            chatBox.ChatMaxMessages,
-            chatBox.ChatShowTimestamps,
-            chatBox.ChatShowBadges,
-            chatBox.ChatMemberColor,
-            chatBox.ChatSuperChatColor);
-    }
-
-    /// <summary>
-    /// Renders the ChatBox preview: real messages when connected, mock when not.
-    /// </summary>
-    private void UpdateChatBoxPreview(Source chatBox, IReadOnlyList<ChatMessage>? messages = null)
-    {
-        try
-        {
-            messages ??= ChatMessages.Count > 0 ? (IReadOnlyList<ChatMessage>)ChatMessages : MockChatMessages;
-            var width = (int)Math.Max(32, chatBox.Width);
-            var height = (int)Math.Max(32, chatBox.Height);
-
-            var frame = _chatBoxRenderer.Render(
-                messages,
-                width,
-                height,
-                chatBox.ChatFontSize,
-                chatBox.ChatFontFamily,
-                chatBox.ChatFontColor,
-                chatBox.ChatBackgroundColor,
-                chatBox.ChatMaxMessages,
-                chatBox.ChatShowTimestamps,
-                chatBox.ChatShowBadges,
-                chatBox.ChatMemberColor,
-                chatBox.ChatSuperChatColor);
-
-            var bitmap = new WriteableBitmap(width, height, 96, 96, System.Windows.Media.PixelFormats.Bgra32, null);
-            bitmap.WritePixels(new System.Windows.Int32Rect(0, 0, width, height), frame.BgraPixels, frame.Stride, 0);
-            chatBox.VideoImageSource = bitmap;
-        }
-        catch (Exception ex) { AppLog.Write($"UpdateChatBoxPreview failed: {ex.Message}"); }
-    }
-
-    private CancellationTokenSource? _mockChatCts;
-
-    private async Task RunMockChatPreviewAsync(Source chatBox, CancellationToken ct)
-    {
-        var n = 0;
-        while (!ct.IsCancellationRequested)
-        {
-            UpdateChatBoxPreview(chatBox, MockChatMessages.Take(n + 1).ToList());
-            await Task.Delay(1000, ct);
-            n++;
-            if (n == MockChatMessages.Count)
-            {
-                await Task.Delay(3000, ct);
-                n = 0;
-            }
-        }
-    }
+        => _chatLayer.RenderFrame(chatBox);
 
     private void StartMockChatPreview()
-    {
-        StopMockChatPreview();
-        _mockChatCts = new CancellationTokenSource();
-        var ct = _mockChatCts.Token;
-        foreach (var chatBox in Scenes.SelectMany(s => s.Elements).OfType<Source>()
-                     .Where(s => s.Type == SourceType.ChatBox && s.ChatPreviewEnabled))
-            _ = RunMockChatPreviewAsync(chatBox, ct);
-    }
+        => _chatLayer.StartMockPreview(Scenes);
 
     private void StopMockChatPreview()
-    {
-        _mockChatCts?.Cancel();
-        _mockChatCts?.Dispose();
-        _mockChatCts = null;
-    }
+        => _chatLayer.StopMockPreview();
 
-    /// <summary>
-    /// Render previews + wire property-change subscriptions for all ChatBox
-    /// sources across every scene. Called after layout load so existing ChatBox
-    /// sources show mock content and respond to config changes.
-    /// </summary>
     private void UpdateActiveChatBoxPreviews()
-    {
-        foreach (var scene in Scenes)
-            foreach (var chatBox in scene.Elements.OfType<Source>().Where(s => s.Type == SourceType.ChatBox))
-            {
-                chatBox.PropertyChanged += (_, e) =>
-                {
-                    if (e.PropertyName is nameof(Source.ChatFontSize) or nameof(Source.ChatFontColor)
-                        or nameof(Source.ChatBackgroundColor) or nameof(Source.ChatBackgroundOpacity)
-                        or nameof(Source.ChatMaxMessages) or nameof(Source.ChatShowTimestamps)
-                        or nameof(Source.ChatShowBadges) or nameof(Source.ChatMemberColor)
-                        or nameof(Source.ChatSuperChatColor) or nameof(Source.ChatFontFamily)
-                        or nameof(Source.ChatFadeSeconds) or nameof(Source.Width) or nameof(Source.Height))
-                        UpdateChatBoxPreview(chatBox);
-                };
-                UpdateChatBoxPreview(chatBox);
-            }
-    }
+        => _chatLayer.UpdateConfiguredBoxes(Scenes);
 }

ViewModels/MainViewModel.cs

@@ -274,7 +274,7 @@ public partial class MainViewModel : ViewModelBase
         _screenCaptureManager.CaptureFailed += (key, message) =>
             AppLog.Write($"ScreenCaptureManager: capture '{key}' failed: {message}");
 
-        _chatBoxRenderer = new ChatBoxRenderer();
+        _chatLayer = new ChatOverlayLayer(new ChatBoxRenderer());
 
         _rtmpUrlProvider = () => _reusableStreamUrl; // TASK 5: the reusable stream's ingest URL
         _framePump = new FramePump(

ViewModels/index.md

@@ -72,5 +72,6 @@ commit, tag `refactor-commit-N`, no per-commit push).
 - [x] **Commit D · `refactor-commit-D`** — **SocialsDialog** → `SocialsDialogViewModel.cs` 515 → **334** + new **`SocialSlotViewModel.cs`** (183 lines). Moved the `DialogEntry` record + the row-level `SocialSlotViewModel` (six-fixed-slot row VM: service/logo/lock/edit/validate state + computed `Show*` flags) into its own file; `SocialsDialogViewModel.cs` keeps the dialog VM (sign-in gate, validation orchestration, commit). `DialogEntry` stays `public` in the same namespace so both files see it. Pending: LayoutStore.
 - [x] **Commit E · `refactor-commit-E`** — **LayoutStore** → `LayoutStore.cs` 1402 split into 6 concern-based partials: **`LayoutStore.cs`** (47: shell — `Instance`, fields, ctor + `EnsureSchema`, `GetUserVersion`, `Dispose`), **`LayoutStore.Migrations.cs`** (495: all `Migrate*` + `EnsureSchema`), **`LayoutStore.Load.cs`** (221: `Load`), **`LayoutStore.Save.cs`** (339: `Save`), **`LayoutStore.Settings.cs`** (292: mic/record-folder/reusable-stream + license/transition/broadcast/hotkey/window `GetSetting`/`UpsertSetting`), **`LayoutStore.Assets.cs`** (41: `GetAssetBytes`/`UpsertAsset`). **PHASE 3 COMPLETE — no production `.cs` over 500.**
 - [x] **Commit F · `refactor-commit-F`** — **Recording (context/concern)** → new **`MainViewModel.Recording.cs`** (121 lines). The encoder (`Services/Encoder/FfmpegEncoder.cs`) and frame pump (`Services/Encoder/FramePump.cs`) were ALREADY extracted services — the planned "extract FFmpegEncoder/StreamHealthMonitor/FramePump" was a no-op premise. The honest functional seam was the local recording-output concern: `StartRecordFile`, `FinalizeRecordingAsync`, `UniquePath`, `ChooseRecordFolder`, `ResetRecordFolder`, `DefaultRecordFolder` + fields `_recordFolder`/`RecordFolderDisplay`/`_activeRecordPath`/`_recordStartTime`/`_recordLength` moved out of the live-stream orchestration. `MainViewModel.Streaming.Operations.cs` 475 → **377**; `MainViewModel.Streaming.cs` 328 → **323**. Same partial class, MVVM glue untouched.
+- [x] **Commit G · `refactor-commit-G`** — **ChatOverlayLayer (true component)** → new **`Services/ChatOverlayLayer.cs`** (199 lines). The first REAL decomposition of the 4,105-line god-object: `MainViewModel.Chat.cs` 194 → **44** (thin delegation). The layer owns all chat behavior — `Messages` buffer, `ChatBoxRenderer`, fade timer, mock-preview timer, per-source preview renders, live-output `RenderFrame`. The VM keeps only the binding surface: `ChatMessages` (delegates to `_chatLayer.Messages`, so XAML bind + LeftPanel `CollectionChanged` hold), `CanAddYouTubeChat`/`ShowChatInactiveMessage` (computed + `OnPropertyChanged` from VM setters), and thin forwards. Scenes are handed in as args (no `Func` seam) so the layer stays scene-graph-free. Zero behavior change; 246 pass / 2 known.
 The partial `.cs` files land next to `MainViewModel.cs` in this folder as the split
 proceeds; each partial carries its own `using`s and re-declares nothing from core.