refactor: split Chat out of MainViewModel — Commit 10/12

MainViewModel.Chat.cs (194 lines) takes the YouTube chat overlay: ChatMessages
(+500 cap, clear-on-fade), OnChatMessageReceived (dispatcher marshal,
mock→real preview switch), chat fade timer (ResetChatFadeTimer), the ChatBox
render paths (RenderChatBox for the live compositor, UpdateChatBoxPreview for
the editor preview), the mock preview loop (MockChatMessages/StartMockChatPreview/
StopMockChatPreview/RunMockChatPreviewAsync/_mockChatCts), UpdateActiveChatBoxPreviews,
CanAddYouTubeChat (one-per-layout gate) and ShowChatInactiveMessage. Core drops
1119 -> 940 lines. Ctor wiring (MessageReceived hookup, ChatBoxRenderer ctor,
LoadLayout preview start, dispose) stays in core; ResolveOutputFrame (core)
still calls RenderChatBox cross-partial.

Zero behavior change; build 0 warnings; 246 pass, only the 2 known failures.
Docs: index.md Chat row added + core row trimmed in the same commit.

ViewModels/MainViewModel.Chat.cs

@@ -0,0 +1,194 @@
+using System.Collections.ObjectModel;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Threading;
+using ytLive.Helpers;
+using ytLive.Models;
+using ytLive.Services;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel : ViewModelBase
+{
+
+    private readonly ChatBoxRenderer _chatBoxRenderer;
+
+    // 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 Add → YouTube Chat menu item: enabled only while no chat layer exists
+    /// anywhere — one chat overlay per layout.</summary>
+    public bool CanAddYouTubeChat
+        => StagedScene != null
+           && !Scenes.Any(s => s.Elements.OfType<Source>().Any(e => e.Type == SourceType.ChatBox));
+
+    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);
+
+            // 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 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;
+            }
+        }
+    }
+
+    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);
+    }
+
+    private void StopMockChatPreview()
+    {
+        _mockChatCts?.Cancel();
+        _mockChatCts?.Dispose();
+        _mockChatCts = 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>
+    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);
+            }
+    }
+}

ViewModels/MainViewModel.cs

@@ -55,22 +55,8 @@ public partial class MainViewModel : ViewModelBase
     private readonly Func<string?> _rtmpUrlProvider;
     private readonly TransitionService _transition = new();
 
-    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.
-    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;
-
     // Branding flash (monetization): a full-frame "made with LlamaCasty!" shown
     // for ~1s every 300s on the live output, ~25% opacity. Paid unlock sets
     // BrandFlashEnabled = false. See ai.md "Monetization".
@@ -96,8 +82,6 @@ public partial class MainViewModel : ViewModelBase
     /// shipped THIRD-PARTY-NOTICES.txt (never opens the OS viewer).</summary>
     public string LicensesText { get; private set; } = string.Empty;
 
-    public ObservableCollection<ChatMessage> ChatMessages { get; } = new();
-
     public SceneElement? SelectedElement
     {
         get => _selectedElement;
@@ -125,12 +109,6 @@ public partial class MainViewModel : ViewModelBase
         }
     }
 
-    /// <summary>The Add → YouTube Chat menu item: enabled only while no chat layer exists
-    /// anywhere — one chat overlay per layout.</summary>
-    public bool CanAddYouTubeChat
-        => StagedScene != null
-           && !Scenes.Any(s => s.Elements.OfType<Source>().Any(e => e.Type == SourceType.ChatBox));
-
     private static readonly SolidColorBrush BarOnBrush = CreateBrush("#2ecc71");
     private static readonly SolidColorBrush BarOffBrush = CreateBrush("#e94560");
     private static SolidColorBrush CreateBrush(string hex)
@@ -141,7 +119,6 @@ public partial class MainViewModel : ViewModelBase
         && !el.IsDraggable && !el.IsWebcam
         && el is not Source { Type: SourceType.Countdown or SourceType.WebSource or SourceType.ChatBox };
 
-    public bool ShowChatInactiveMessage => !IsLive;
     public bool ShowPreviewPlaceholder => !ShowEmptySceneHint && ActiveBackgroundImage == null && BackgroundImage == null;
 
     // Paid unlock flips this off (see ai.md "Monetization"). When disabled the
@@ -903,49 +880,6 @@ public partial class MainViewModel : ViewModelBase
         Process.Start(new ProcessStartInfo(url) { UseShellExecute = true });
     }
 
-    private void OnChatMessageReceived(ChatMessage message)
-    {
-        System.Windows.Application.Current.Dispatcher.Invoke(() =>
-        {
-            ChatMessages.Add(message);
-            if (ChatMessages.Count > 500)
-                ChatMessages.RemoveAt(0);
-
-            // 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();
-    }
-
     // Scene-element → latest frame, for the live compositor. The map mirrors the
     // preview: webcam by DeviceId, live captures (the background) by CaptureKey,
     // images/background by AssetId. A null frame leaves the element transparent.
@@ -962,119 +896,6 @@ public partial class MainViewModel : ViewModelBase
         };
     }
 
-    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;
-            }
-        }
-    }
-
-    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);
-    }
-
-    private void StopMockChatPreview()
-    {
-        _mockChatCts?.Cancel();
-        _mockChatCts?.Dispose();
-        _mockChatCts = 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>
-    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);
-            }
-    }
-
     // The tier's crop rect over the 1920x1080 master, integer-aligned (the VM's
     // OutputRect* are doubles — the vertical 607.5 half-pixel crop rounds to 608).
     private CompositorOptions BuildCompositorOptions()

ViewModels/index.md

@@ -8,7 +8,7 @@ areas' docs in their own rows keeps this index small to read.
 
 | File | Purpose |
 |------|---------|
-| `MainViewModel.cs` | Core. `public partial class MainViewModel : ViewModelBase`. **Source commands + element rows:** scenes are pure selection rows; sources carry edit/visibility/trash (`EditElementCommand` sets `element.IsEditing`, `ToggleElementVisibilityCommand` flips `IsVisible`, `RemoveSourceCommand`; Backdrop trash slot reserved via `HiddenBoolToVisibilityConverter` — TASK 13); shared `NextSourceName` (Image, Image2, Image3… no-space increment from actual names — used by `AddSource` + `AddReusedImage`), `AddImageCommand`. **Overlays/lifecycle:** fields + ctor wiring (all command assignments, mixer/camera/chat/hotkey/subscription hookups), `Shutdown`/`SaveLayoutNow`/`ScheduleSave`/`LoadLayout`, `SetPanel`/`ShowOverlay`/`ShowLicenses`, `CreateBrush` + shared `BarOnBrush`/`BarOffBrush` (referenced by Audio/Trax/Socials partials), `OpenUrl`/`ComposeEmail`/`SubmitBug`/`SubmitFeature`, window-geometry pass-through, `SelectedElement`/`OnSelectedElementPropertyChanged`, `ShowPreviewPlaceholder`/`ShowChatInactiveMessage`, `BrandFlash*`, WebView2 hosting (`InitWebView2`/`RegisterLoadedWebSources`/`OnWebView2PreviewBitmapChanged`), frame-pump wiring (construction + `_rtmpUrlProvider` seam + `Dispose`) — the pump's stream-state consumers live in the Streaming partial. |
+| `MainViewModel.cs` | Core. `public partial class MainViewModel : ViewModelBase`. **Source commands + element rows:** scenes are pure selection rows; sources carry edit/visibility/trash (`EditElementCommand` sets `element.IsEditing`, `ToggleElementVisibilityCommand` flips `IsVisible`, `RemoveSourceCommand`; Backdrop trash slot reserved via `HiddenBoolToVisibilityConverter` — TASK 13); shared `NextSourceName` (Image, Image2, Image3… no-space increment from actual names — used by `AddSource` + `AddReusedImage`), `AddImageCommand`. **Overlays/lifecycle:** fields + ctor wiring (all command assignments, mixer/camera/chat/hotkey/subscription hookups), `Shutdown`/`SaveLayoutNow`/`ScheduleSave`/`LoadLayout`, `SetPanel`/`ShowOverlay`/`ShowLicenses`, `CreateBrush` + shared `BarOnBrush`/`BarOffBrush` (referenced by Audio/Trax/Socials partials), `OpenUrl`/`ComposeEmail`/`SubmitBug`/`SubmitFeature`, window-geometry pass-through, `SelectedElement`/`OnSelectedElementPropertyChanged`, `ShowPreviewPlaceholder`, `BrandFlash*`, WebView2 hosting (`InitWebView2`/`RegisterLoadedWebSources`/`OnWebView2PreviewBitmapChanged`), frame-pump wiring (construction + `_rtmpUrlProvider` seam + `Dispose`, plus `ResolveOutputFrame` → `RenderChatBox` for chat layers) — the pump's stream-state consumers live in the Streaming partial. |
 | `MainViewModel.Account.cs` | Session + connected account: `LoadSavedSessionAsync` (DPAPI restore at startup), `SignInAsync`/`ChangeAccountAsync`/`SignOutYouTubeAsync`, `IsConnected`/`AccountAvatarUrl`/`AccountDisplayName`/`AccountStatusLightToolTip` via `SyncConnectedAccount` (cleared on End). |
 | `MainViewModel.License.cs` | Polar license (freemium): `LicenseKey`/`LicenseMessage`/`IsLicenseValidating`/`IsLicenseEntryOpen`/`IsHubVisible`/`IsPremium`, `OfflineGracePeriod`, `ValidateLicenseAtStartupAsync`/`ActivateLicenseAsync`. |
 | `MainViewModel.Scenes.cs` | Five-scene catalog: `Scenes` + `StagedScene`/`LiveScene`/`IsEditMode`, `AddScene` (canonical names only), `MissingScenes`/`ShowAddScene`/`AddSceneCommand`; scene wiring `OnScenesChanged`/`WireScene`/`UnwireScene`; transitions `SelectedTransitionType`/`TransitionDurationMs`/`TransitionToScene`/`ApplyTransitionToLive`; global hotkeys `HandleHotkey`/`OpenHotkeyConfig`/`RefreshHotkeyLabels`; scene-gating hints (`CanChangeBackground`). |
@@ -18,6 +18,7 @@ areas' docs in their own rows keeps this index small to read.
 | `MainViewModel.Trax.cs` | Background music (TASK 9, rides the loopback into the stream): `_musicPlayer` (`MusicPlayer`), `IsMusicPlaying`/`TraxError`/`TraxDotBrush`/`TraxToolTip`, interaction `TraxLeftClick`/`TraxRightClick`/`PickTraxTrack`, playback `LoadTrax`/`PlayTrax`/`PauseTrax`/`OnTraxPlaybackEnded`/`RefreshTraxUi`, `UpdateTraxLocalGain` (mirrors the game bar's mute onto `MusicPlayer.LocalGain` so the track ducks/restores with desktop audio). |
 | `MainViewModel.Socials.cs` | Social bar (global resource, overlaid on every scene): `_socials`/`_socialBarFrame`/`_socialValidator` (`ISocialValidator`/`HttpSocialValidator`), `HasSocials`/`SocialBarVisible`/`SocialBarDotBrush`/`SocialBarGlowBrush`/`Socials`/`SocialBarTop`, `OpenSocialDialogCommand`/`OpenSocialDialog` (spawns `SocialsDialogViewModel` + window; saved copy replaces `_socials`), `NotifySocialsChanged`/`RenderSocialBarFrame` (`SocialBarRenderer` → immutable `_socialBarFrame` the frame pump reads), fediverse heal `HealFediverseSoftwareAsync` (static, test-facing) + `HealFediverseSoftwareInBackground`, bar edge toggle `SetSocialBarPosition`/`ToggleSocialBarPosition`. `BarOnBrush`/`BarOffBrush`/`CreateBrush` stay in core (shared tokens). |
 | `MainViewModel.Streaming.cs` | Go-live/record + health + quality tiers + session UI. **Stream state:** `StreamStatus`/`StreamVisibility` setters + `_streamStatus` field, `IsOffline`/`IsLive`/`IsLivePrivate`. **Go-live flow:** `StartSession` (routes by pill state) → `BeginRecordOnly` (signed-out local recording) or `BeginGoLive` (GoLive dialog → captures title/description/visibility + `BroadcastForm.CaptureGoLive` → `PrepareAndStartLiveAsync`: reusable stream → `CreateBroadcast` (stores `_currentBroadcastId`) → empty-metadata warn → chat poll start (liveChatId) → `_framePump.StartAsync()` + health poll; failures → `StreamStatus.Error`, never a crash); `StartRecordFile` (auto-named `ty-…-0000.mp4`) + `FinalizeRecordingAsync` (rename modal, `UniquePath`); `StopStream` (posts Offline, stops chat/audio pipe/pump, clears `_currentBroadcastId`; session/token deliberately NOT cleared — sign-out stays explicit). **Health:** `CurrentHealth`/`ResetHealth`/`ApplyHealth`/`OnFramePumpHealthUpdated` (marshal `FramePump.HealthUpdated` off the stderr thread), `PollHealthAsync`/`OnHealthPollTick`/`ApplyHealthIssue` (report-by-exception banner `HealthIssueBanner`/`HealthIssueBackground` via `StreamHealthReporter`). **Session timer:** `_liveTimer` (ctor-wired) `UpdateSessionTimer`/`OnLiveTimerTick`/`LiveElapsedText`/`_recDotPulse`. **Start/End UI:** REC/ON-AIR pills (`RecordPillOn`/`OnAirPillOn`/`CanToggleOnAir`), `ShowPrimaryStartButton`/`CanStartSession`/`ShowEndStreamButton`/`EndButtonText`/`ShowLogInButton`, REC sign `RecDotBrush`/`RecTextBrush`/`RecDotOpacity`/`OnAirBrush`, live window tokens `WindowTitle`/`TopBarBackground`/`PreviewGlow*` via `UpdateLiveVisuals`; `ChooseRecordFolder`/`ResetRecordFolder`/`_recordFolder`/`RecordFolderDisplay`/`DefaultRecordFolder`. **Resolution dropdown:** `QualityOptions`/`SelectedQuality`/`ResolutionHelp`/`ApplyStreamQuality` + `OutputRect*`/`DimRects`/`IsOutputCropped`/`ResolutionBadgeText` over the 1920×1080 master. **Pipeline bits:** `_framePump`/`_liveTimer`/`_healthPollTimer` fields, `BuildEncoderOptions`. Commands `StartStreamCommand`/`EndStreamCommand`/`ChooseRecordFolderCommand`/`ResetRecordFolderCommand`. Broadcast pull-out: `CurrentBroadcastId`/`BroadcastForm`. |
+| `MainViewModel.Chat.cs` | Chat overlay + preview pipeline: `ChatMessages` (500-message cap; clear-on-fade), `OnChatMessageReceived` (marshal `_youtubeChat.MessageReceived` onto the dispatcher, switch previews mock→real), fade `_chatFadeTimer`/`ResetChatFadeTimer` (shortest `ChatFadeSeconds` across chat layers); live render `RenderChatBox` (called from `ResolveOutputFrame`, stays in core) + preview render `UpdateChatBoxPreview` (bitmap onto `chatBox.VideoImageSource`); mock preview `MockChatMessages`/`StartMockChatPreview`/`StopMockChatPreview`/`RunMockChatPreviewAsync`/`_mockChatCts`; `UpdateActiveChatBoxPreviews` (wires Chat* property-change subscriptions + first render); `CanAddYouTubeChat` (one-per-layout gate), `ShowChatInactiveMessage` (`!IsLive`). `_chatBoxRenderer` field. Ctor wiring (`MessageReceived` hookup, `new ChatBoxRenderer()`, `LoadLayout` preview start, `_youtubeChat.Dispose`) stays in core. |
 | `GoLiveViewModel.cs` | Start Stream dialog: **account row** (saved channel shown with Change Account, or Sign in to YouTube; Start gated on `IsSignedIn`/`IsBusy`) + title/description + **locked Visibility (always "Private" — ship step 7, no dropdown)**, start/cancel requests |
 | **About hub (TASK 11, in `MainViewModel`)** | the About overlay is the in-app creator hub: `ChannelUrl`/`MastodonUrl`/`CoffeeUrl` (public consts, live) + `PremiumUrl` (tabled billing seam — TASK 12 → the greyed "Unlock Premium" button lights up when filled); `OpenLicensesCommand` → `ShowLicenses()` loads the shipped `THIRD-PARTY-NOTICES.txt` into `LicensesText` and sets `IsLicensesOpen` (in-app scrolling panel, never the OS viewer); `BackToAbout_Click` in `MainWindow.xaml.cs` flips it off. |
 | `ReuseImageViewModel.cs` | Add Image dialog: candidate list (`ReuseImageCandidate`), reuse/new/cancel |
@@ -47,7 +48,7 @@ Progress (Commit N/12 · tag):
 - [x] **Commit 7/12 · `refactor-commit-7`** — **Trax** → `MainViewModel.Trax.cs`
 - [x] **Commit 8/12 · `refactor-commit-8`** — **Socials** → `MainViewModel.Socials.cs`
 - [x] **Commit 9/12 · `refactor-commit-9`** — **Streaming** → `MainViewModel.Streaming.cs`
-- [ ] **Commit 10/12** — **Chat** (YouTube chat + mock preview + chatbox render)
+- [x] **Commit 10/12 · `refactor-commit-10`** — **Chat** → `MainViewModel.Chat.cs`
 - [ ] **Commit 11/12** — **Overlays** (settings/bug/feature/about panels + license entry)
 
 The partial `.cs` files land next to `MainViewModel.cs` in this folder as the split