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

TASKS/task-03-capture-pipeline.md

@@ -5,7 +5,7 @@
 
 **Goal:** Real video preview in the center panel — the minimal source set below, composited per scene.
 
-### Status: 🔶 In progress — 27 of 30 items done (1 excluded: background removal); items 16, 17, 20 open
+### Status: 🔶 In progress — **Alerts (item 20) SHIPPED 2026-09-24 via TASK 43**; still open: item 17 (Text source), item 20's `RewardEvents` SQLite persistence half (16 compositing + 19 background removal excluded)
 
 1. ✅ **Milestone 1 — webcam** — MediaCapture (WinRT SDK projection) with device enumeration, CPU-first frame source, refcounted `CameraManager`, picker dialog, clip shapes (Traditional + Round) + mirror, 480×270 default placement — schema v2
 2. ✅ **Schema v3 (Ship Branch A)** — multi-scene webcam (singleton `Webcam` + per-scene `WebcamSceneConfig`), right-click border/context menu, static OBS-style borders, 50%-per-dimension webcam size cap, device-swap (`ReleaseAllAsync`) — 25 tests passing
@@ -26,7 +26,19 @@
 17. ☐ **Text source** — live text ("Starting soon", "Back in 5", handle, callout)
 18. ✅ **Chat box** — YouTube live chat rendered *on* the stream so viewers read along in-video — `ChatBoxRenderer` (WPF FormattedText → VideoFrame), configurable font size/color/badges/timestamps/max-messages via Elements panel, schema v10, persisted across save/load
 19. ❌ **Background removal (milestone 2)** — ONNX Runtime + DirectML, MediaPipe Selfie Segmentation — deliberately NOT in this build
-20. ☐ **Alerts** — Super Chat / membership / subscribe pop-ins; build after the six; **free and ungated** (the stale "one paid feature" label predates the 2026-08-31 monetization reversal and is corrected 2026-09-01 — the paid swap is the branding flash ONLY; see Monetization in `ai.md`). **v1 IN** per the complete-v1 ruling. **Precursor — reward-event capture (2026-09-01):** Alerts render from the app's canonical `RewardEvent` feed (all 7 `liveChatMessage` reward types, persisted to SQLite + the session report — see TASK 10 → "Related work — monetization awareness"), so it consumes that already-built data rather than re-integrating `liveChatMessages`. That capture is the required prior milestone.
+20. ✅ **Alerts — Super Chat / membership pop-ins (SHIPPED 2026-09-24 via TASK 43, NATIVE)** —
+    free and ungated (see Monetization in `ai.md`). **v1 IN** per the complete-v1 ruling. The
+    deliverable is now **native events + native animations, no third-party widget**: the chat feed
+    (`liveChat/messages`, six types decoded — TASK 43 half 1) drives a `SourceType.AlertBox`
+    ("Stream Alerts", one celebration zone per layout) where each event plays its **own unique
+    branded animation** (`AlertRenderer`/`AlertOverlayLayer`, 33ms ticker, `Advance` test clock).
+    **Creator rulings:** a free-subscriber mention is a plain chat row — NO sub alert (YouTube
+    emits no public event for free subs), NO viewer count (vetoed), and every card draws the
+    "made with LlamaCasty!" brand line (each broadcast = free product placement). **Precursor
+    (still open): the reward-event persistence half — the canonical `RewardEvents` SQLite table
+    (all six types persisted per broadcast) + `superChatEvents.list` backfill + the session-report
+    rollup (TASK 10 → "Related work — monetization awareness"). The shipped alert path parses
+    events into `ChatMessage` directly in memory; the report reads that table once it exists.**
 21. ✅ **Show Desktop toggle** — `Source.ShowDesktop` bool persisted in DB (schema migration + LayoutStore read/write). When checked, primary monitor captures regardless of fullscreen game state. Toggling off falls back to running game or releases to static placeholder. `ClearBackdropCaptureAsync` clears `CaptureKey` + `VideoImageSource` so static fallback renders. Toggle on Live backdrop context menu (IsCheckable MenuItem).
 22. ✅ **Top bar — status light + avatar + Log In button** — red/green/pulsing ellipse (disconnected/connected/live). Avatar border visible only when connected, loads via `BitmapImage` code-behind. "Log In" button visible when disconnected, calls `StartStreamCommand` → GoLiveWindow. `ShowStartStream` now requires `IsConnected`.
 23. ✅ **Chat preview — one-at-a-time mock messages** — `RunMockChatPreviewAsync`: simple async loop, displays `MockChatMessages[n]` via `Take(n+1)`, 1000ms between messages, wraps at end. `ChatPreviewEnabled` property on Source (default true). Stops on real messages, restarts on fade timer clear.
@@ -53,10 +65,12 @@ the hot few and nothing esoteric. If a user needs more, they've graduated to OBS
 4. **Image** — a floating graphic/logo overlay (watermark, badge, corner branding). Free-positioned.
 5. **Text** — live text ("Starting soon", "Back in 5", handle, callout). Casual streamers live on this.
 6. **Chat box** — YouTube live chat rendered *on* the stream so viewers read along in-video. YT-native.
-7. **Alerts** — Super Chat / membership / subscribe pop-ins. The dopamine source. **The one big lift**
-   (Super Chat event streaming + on-stream rendering/animation); build after the six. **Free and
-   ungated** — paid = flash removal only (stale "one paid feature" corrected 2026-09-01). Consumes
-   the canonical `RewardEvent` feed (reward-event capture, TASK 10 → related work).
+7. **Alerts** — Super Chat / membership pop-ins. The dopamine source. **The one big lift — DONE
+   (2026-09-24, TASK 43): native events + native animations.** One `SourceType.AlertBox`
+   celebration zone; six event types = six unique branded animations; free-sub mention = chat row
+   only; no viewer count. **Free and ungated** — paid = flash removal only (corrected 2026-09-01).
+   Pending: the `RewardEvents` SQLite persistence half (item 20; the report + journey read it,
+   TASK 10 → related work).
 
 Deliberately NOT supported: game capture, browser source, media playlist, VLC, color-key voodoo, MIDI.