feat(alerts): TASK 43 — native events & alerts (six unique animations) + chat parity

Replace the external StreamElements feed with NATIVE YouTube events per the creator's
2026-09-23 question.

Chat parity half:
- YouTubeChatService decodes ALL SIX liveChat/messages event types into
  ChatMessage.Kind (superChat/superSticker/newSponsor/membershipGifting/
  giftMembershipReceived/memberMilestoneChat) — the four formerly-empty overlay
  rows are real now — and re-arms its one-shot poll on the server's
  pollingIntervalMillis (streamList connection semantics; clamp 1000-6000ms,
  maxResults=2000). ParsePage internal static seam + ChatPage record for
  deterministic tests; optional HttpClient ctor seam kept; InjectSimulatedMessage
  (TASK 41) preserved.

Alerts half (creator rulings: one celebration zone, six UNIQUE animations, no
menus/polls, sub mention = chat row only, NO viewer count):
- New SourceType.AlertBox 'Stream Alerts' (one per layout, CanAddAlerts gate
  mirroring chat; idle = transparent).
- AlertRenderer: six distinct branded animations (SuperChat slide-up/shine/
  count-up, SuperSticker scale-pop, NewMember drop-in/flash, MemberGift slide-left/
  chip-fan, GiftReceived confetti, MemberMilestone rise/growth-bar), every card
  drawing the 'made with LlamaCasty!' brand line.
- AlertOverlayLayer: true component (Commit-G pattern) — queue (cap 10, drop tail
  never stall), 33ms UI ticker, cache-first RenderFrame + UpdatePreview,
  Advance(double) as the deterministic test clock; ChatEventKind.None rows never
  enqueue.
- Wired: resolver RenderAlertBox, _alertLayer ctor + dispose, LoadLayout previews,
  Add menu item (Controls/LeftPanel.xaml), TestSessionViewModel sims tagged
  (member->NewMember, superchat->SuperChat).

Good Dog ONE integration test: AlertLayerTests (RealApp STA, real WPF raster) —
ParsePage classifies all six kinds + cadence fields; None rows enqueue nothing;
six events play pairwise-distinct moving frames then drain to null.

Gate: clean build 0 warnings; full suite 316/317, the one failure
(LayerReorderPersistenceTests.RealMouseDrag) repros on the clean tree — the
known environmental class (real-mouse-drag no-ops with a game/fullscreen window
focused).

References (OBS/overlay ecosystem):
- streamList semantics: https://developers.google.com/youtube/v3/live/docs/liveChatMessages/streamList
- OBS alert-box pattern (designated celebration zone, idle transparent): creator-chosen model

ViewModels/MainViewModel.Chat.cs

@@ -10,6 +10,7 @@ public partial class MainViewModel : ViewModelBase
 {
 
     private readonly ChatOverlayLayer _chatLayer;
+    private readonly AlertOverlayLayer _alertLayer;
 
     /// <summary>The live chat message buffer — the same collection the
     /// <see cref="ChatOverlayLayer"/> owns; here so XAML can bind it and the
@@ -22,10 +23,19 @@ public partial class MainViewModel : ViewModelBase
         => StagedScene != null
            && !Scenes.Any(s => s.Elements.OfType<Source>().Any(e => e.Type == SourceType.ChatBox));
 
+    /// <summary>The Add → Stream Alerts menu item: one alert zone per layout
+    /// (multiple zones would double-play every event).</summary>
+    public bool CanAddAlerts
+        => StagedScene != null
+           && !Scenes.Any(s => s.Elements.OfType<Source>().Any(e => e.Type == SourceType.AlertBox));
+
     public bool ShowChatInactiveMessage => !IsLive;
 
     private void OnChatMessageReceived(ChatMessage message)
-        => _chatLayer.OnMessageReceived(message, Scenes);
+    {
+        _chatLayer.OnMessageReceived(message, Scenes);
+        _alertLayer.OnMessageReceived(message, Scenes);
+    }
 
     private void UpdateChatBoxPreview(Source chatBox, IReadOnlyList<ChatMessage>? messages = null)
         => _chatLayer.UpdatePreview(chatBox, messages);
@@ -33,6 +43,12 @@ public partial class MainViewModel : ViewModelBase
     private VideoFrame? RenderChatBox(Source chatBox)
         => _chatLayer.RenderFrame(chatBox);
 
+    private void UpdateAlertBoxPreview(Source alertBox)
+        => _alertLayer.UpdatePreview(alertBox);
+
+    private VideoFrame? RenderAlertBox(Source alertBox)
+        => _alertLayer.RenderFrame(alertBox);
+
     private void StartMockChatPreview()
         => _chatLayer.StartMockPreview(Scenes);
 
@@ -41,4 +57,7 @@ public partial class MainViewModel : ViewModelBase
 
     private void UpdateActiveChatBoxPreviews()
         => _chatLayer.UpdateConfiguredBoxes(Scenes);
+
+    private void UpdateActiveAlertBoxPreviews()
+        => _alertLayer.UpdateConfiguredBoxes(Scenes);
 }

ViewModels/MainViewModel.Sources.cs

@@ -29,15 +29,18 @@ public partial class MainViewModel
             SourceType.Countdown => "Countdown",
             SourceType.WebSource => "Web Resource",
             SourceType.ChatBox => "YouTube Chat",
+            SourceType.AlertBox => "Stream Alerts",
             _ => "Layer",
         };
 
         // The (+) menu only adds regular layers. The Background is a locked
         // per-screen layer managed by EnsureBackground/NormalizeBackgrounds —
-        // never user-created, never deleted. YouTube Chat is one-per-layout.
+        // never user-created, never deleted. YouTube Chat and Stream Alerts
+        // are one-per-layout.
         if (sourceType is SourceType.DisplayCapture or SourceType.WindowCapture or SourceType.Background)
             return;
-        if (sourceType == SourceType.ChatBox && !CanAddYouTubeChat)
+        if ((sourceType == SourceType.ChatBox && !CanAddYouTubeChat)
+            || (sourceType == SourceType.AlertBox && !CanAddAlerts))
             return;
 
         // Web resources use "Web Resource-N" naming (0-indexed per scene)
@@ -48,10 +51,10 @@ public partial class MainViewModel
                 ? $"{baseName}-{webCount}"
                 : NextSourceName(scene, baseName),
             Type = sourceType,
-            X = sourceType == SourceType.ChatBox ? 1400 : 0,
-            Y = sourceType == SourceType.ChatBox ? 20 : 0,
-            Width = sourceType == SourceType.WebSource ? 640 : sourceType == SourceType.ChatBox ? 500 : 0,
-            Height = sourceType == SourceType.WebSource ? 480 : sourceType == SourceType.ChatBox ? 648 : 0,
+            X = sourceType == SourceType.ChatBox ? 1400 : sourceType == SourceType.AlertBox ? 620 : 0,
+            Y = sourceType == SourceType.ChatBox ? 20 : sourceType == SourceType.AlertBox ? 430 : 0,
+            Width = sourceType == SourceType.WebSource ? 640 : sourceType == SourceType.ChatBox ? 500 : sourceType == SourceType.AlertBox ? 680 : 0,
+            Height = sourceType == SourceType.WebSource ? 480 : sourceType == SourceType.ChatBox ? 648 : sourceType == SourceType.AlertBox ? 200 : 0,
         };
         _sceneGraph.AddElement(scene, source);
 

ViewModels/MainViewModel.cs

@@ -308,6 +308,7 @@ public partial class MainViewModel : ViewModelBase
         _mediaManager.MediaFailed += OnMediaFailed;
 
         _chatLayer = new ChatOverlayLayer(new ChatBoxRenderer());
+        _alertLayer = new AlertOverlayLayer(new AlertRenderer());
 
         _rtmpUrlProvider = () => _reusableStreamUrl; // TASK 5: the reusable stream's ingest URL
         _framePump = new FramePump(
@@ -397,6 +398,7 @@ public partial class MainViewModel : ViewModelBase
         StagedScene = Scenes.FirstOrDefault();
         UpdateActiveBackground();
         UpdateActiveChatBoxPreviews();
+        UpdateActiveAlertBoxPreviews();
         StartMockChatPreview();
         UpdateBackgroundImage();
         ReacquireWebcam();
@@ -437,6 +439,7 @@ public partial class MainViewModel : ViewModelBase
         _layoutStore.Dispose();
         _musicPlayer.Dispose();
         _youtubeChat.Dispose();
+        _alertLayer.Dispose();
     }
 
     public void SaveLayoutNow()
@@ -520,6 +523,7 @@ public partial class MainViewModel : ViewModelBase
             WebcamSceneConfig webcam => _cameraManager.GetLatestFrame(DeviceKeyForWebcam(webcam.WebcamId)),
             Source { IsLiveCapture: true, CaptureKey: not null } live => _screenCaptureManager.GetLatestFrame(live.CaptureKey),
             Source { Type: SourceType.ChatBox } chatBox => RenderChatBox(chatBox),
+            Source { Type: SourceType.AlertBox } alertBox => RenderAlertBox(alertBox),
             Source { Type: SourceType.WebSource } web => _webView2Manager?.GetLatestFrame(web.Id),
             Source { IsMediaSource: true, MediaPath: not null } media => _mediaManager.GetLatestFrame(media.MediaPath),
             Source { AssetId: not null } image => StaticPixelCache.Get(image.AssetId),

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`. **Lifecycle/ctor wiring:** fields + ctor wiring (all command assignments, mixer/camera/chat/hotkey/subscription hookups), `Shutdown`/`SaveLayoutNow`/`ScheduleSave`/`LoadLayout`, `CreateBrush` + shared `BarOnBrush`/`BarOffBrush` (referenced by Audio/Trax/Socials partials), 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.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`. **Lifecycle/ctor wiring:** fields + ctor wiring (all command assignments, mixer/camera/chat/hotkey/subscription hookups), `Shutdown`/`SaveLayoutNow`/`ScheduleSave`/`LoadLayout`, `CreateBrush` + shared `BarOnBrush`/`BarOffBrush` (referenced by Audio/Trax/Socials partials), window-geometry pass-through, `SelectedElement`/`OnSelectedElementPropertyChanged`, `ShowPreviewPlaceholder`, `BrandFlash*`, WebView2 hosting (`InitWebView2`/`RegisterLoadedWebSources`/`OnWebView2PreviewBitmapChanged`), frame-pump wiring (construction + `_rtmpUrlProvider` seam + `Dispose`, plus `ResolveOutputFrame` → `RenderChatBox`/`RenderAlertBox` for chat + alert 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`). |
@@ -19,7 +19,7 @@ areas' docs in their own rows keeps this index small to read.
 | `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:** mode switch `RecordPillOn`/`OnAirPillOn`, top-bar worlds (`ShowIdleWorld`/`ShowRecordAction`/`ShowStreamActions`/`ShowSignInButton`/`ShowAvatarButton`, reality line `RunningVisible`/`RunningText`/`RunningDotBrush`, Test gate `ShowTestButton`/`CanStartTest` — `RaiseTopBarModes()`), `ShowPrimaryStartButton`/`CanStartSession`/`ShowEndStreamButton`/`EndButtonText`, 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.Overlays.cs` | Settings/bug/feature/about panels + creator-hub links: panel state `IsSettingsOpen`/`IsBugOpen`/`IsFeatureOpen`/`IsAboutOpen` (via `SetPanel` → `IsAnyOverlayOpen`), `IsLicensesOpen` (flips `IsHubVisible`), `OverlayTitle`, `ShowOverlay` (one-panel exclusivity) + `ShowLicenses` (loads shipped `THIRD-PARTY-NOTICES.txt` into `LicensesText` on first open, never the OS viewer); bug/feature report `BugReportText`/`BugReportEmail`/`FeatureRequestText`/`FeatureRequestEmail` + `SubmitBug`/`SubmitFeature`/`ComposeEmail`/`OpenUrl`; About hub consts `ChannelUrl`/`MastodonUrl`/`CoffeeUrl` (public, integration-test live) + `PremiumUrl` (tabled billing seam — TASK 12 → greyed "Unlock Premium" lights up when filled) + `IsPremiumAvailable` + `SupportEmail` + `AppVersionLabel`; commands `OpenSettingsCommand`/`OpenBugCommand`/`OpenFeatureCommand`/`OpenAboutCommand`/`CloseOverlayCommand`/`SubmitBugCommand`/`SubmitFeatureCommand`/`OpenChannelCommand`/`OpenMastodonCommand`/`OpenCoffeeCommand`/`OpenPremiumCommand`/`OpenLicensesCommand`. Ctor command assignments stay in core. |
-| `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. |
+| `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, then feed **both** component layers), 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`). **Alerts (TASK 43):** same facade for the native alert box — `_alertLayer` (`AlertOverlayLayer`), `RenderAlertBox`/`UpdateAlertBoxPreview`, `UpdateActiveAlertBoxPreviews`, `CanAddAlerts` (one alert zone per layout). Ctor wiring (`MessageReceived` hookup, `new ChatBoxRenderer()`, `new AlertRenderer()`, `LoadLayout` preview start, `_youtubeChat.Dispose` + `_alertLayer.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.Overlays.cs`)** | 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 |