feat(stream): TASK 41 Test Stream mode — private test broadcast + TEST drawer

Test button next to Start runs the real private-only go-live pipeline as a
session variant (IsTestStream): BeginTestStream -> extracted
StartStreamingSession(alsoRecord:false) shared with the dialog path — no Go
Live dialog, no 'last live' stamp, no recording. Gold top bar + TEST badge +
'End Test' button face; TEST drawer (third right-rail pull-out, three-way
exclusivity) auto-opens once the liveChatId resolves.

Chat tooling: Mock Chat Input sends a REAL liveChat/messages.insert
(YouTubeStreamService.InsertChatMessageAsync) that round-trips the real ~2s
poll and renders through the live overlay; simulated Subscriber/New
Member/Super Chat events inject through the poller's MessageReceived seam
(YouTubeChatService.InjectSimulatedMessage, ChatMessage.IsSimulated) — the
insert API only creates textMessageEvent, so non-text events are local-only
by design (ref: developers.google.com/youtube/v3/live/docs/liveChatMessages/insert).
Scopes youtube + youtube.force-ssl already cover insert; no re-consent.

Good Dog: ytLive.Tests/TestStreamTests.cs — coordinator protocol with fake
HTTP + real-window drawer exclusivity/gate. 0 warnings; 314/314 pass (clean
run; intermittent host abort is the pre-existing WinRT-webcam flake).

Docs ride in the same change: TASKS.md row 41, TASKS/task-41-test-stream-mode.md,
ai.md (YouTube Live API constraints), HANDOFF rewrite.

TASKS/task-41-test-stream-mode.md

@@ -0,0 +1,82 @@
+# TASK 41 — Test Stream mode: private test broadcast + TEST drawer
+
+**Status:** ✅ Done (2026-09-22) — one scope-checked work unit, one Good Dog integration test,
+314/314 suite green, 0 warnings.
+
+## Creator ask (2026-09-22)
+
+"YouTube Test Stream & Chat Integration": a **Test/Preview** button beside Start that runs a
+private broadcast via the API, monitors stream/ingest, activates the chat endpoint (liveChatId),
+and provides a **chat simulator**: mock chat input (`liveChatMessages.insert`) + a toggle to
+inject mock chat, with alert/event triggers for subscriber, membership, and Super Chat.
+
+## Locked decisions (user answers, 2026-09-22)
+
+- **Chat-overlay events only** — simulated events validate the existing chat overlay styling
+  (text / member `memberColor` / SuperChat `superChatColor` rows). Dedicated stinger/TTS alert
+  widgets are NOT part of this task — they stay queued under **TASK 3 items 16/17/20**.
+- **TEST drawer in the right rail** — third white tab below YPP, three-way one-open-at-a-time
+  exclusivity, auto-opens when a test broadcast boots.
+- **Hybrid simulation** — text = REAL `liveChat/messages.insert` (round-trips the real 2s poll
+  and renders through the live overlay path); member/SuperChat/subscriber = **local injection** at
+  the poller's `MessageReceived` seam (marked `IsSimulated`). YouTube's insert API only creates
+  `textMessageEvent`s — non-text events are local-only by design.
+
+## Facts the build sits on (verified in code, 2026-09-22 research pass)
+
+- **The app is already private-only go-live** — `YouTubeStreamService.CreateBroadcast` hardcodes
+  `privacyStatus="private"` + `enableAutoStart/Stop` + `low latency`, no monitor stream
+  (`enableMonitorStream=false`), and the Go Live dialog is locked to Private. "Test" is therefore a
+  **session variant over the real pipeline**, not a new broadcast mode.
+- The **liveChatId flow already exists**: `GetBroadcastLiveChatIdAsync` → `_youtubeChat.Start(liveChatId)`
+  in `PrepareAndStartLiveAsync` — the "chat endpoint activation" the ask describes.
+- OAuth scope already includes `youtube` + `youtube.force-ssl` (`YouTubeAuthService.cs:18`) —
+  enough for `liveChat/messages.insert`; no re-consent.
+- Chat = **polling** (`YouTubeChatService`, 2s): no webhook exists or is planned.
+- No alert system exists anywhere in the codebase (grep verified) — hence the scope decision above.
+- Existing mock-chat *preview* (`ChatOverlayLayer.StartMockChatPreview`) is static placeholders,
+  not live-injectable — separate from this task.
+
+## What shipped (TASK 41, 2026-09-22)
+
+- **`Controls/TopBar.xaml`** — **Test** button (secondary style) left of Start; visible only when
+  `ShowTestButton` (offline ∧ not recording ∧ signed-in); **TEST** amber badge while
+  `IsTestStream` (next to the elapsed clock).
+- **`Controls/PreviewPane.xaml`** — **TEST** tab (gold text, below YPP on the rail) + TEST drawer:
+  session caption / liveChatId line, **Mock Chat Input** (TextBox + Send), **SIMULATED EVENTS**
+  (Subscriber / New Member / Super Chat buttons), live feedback line, footer "End Test" + the
+  "private, same pipeline as a real live" note; drawer exclusivity wired three-way.
+- **`Services/TestSessionViewModel.cs`** (NEW) — the TEST drawer VM: `BeginTest(broadcastId,
+  liveChatId)` (auto-opens the dock once the liveChatId resolves), `SendTestMessageAsync` → real
+  insert, `Simulate{Subscriber,Member,SuperChat}Command` → `InjectSimulatedMessage`, `EndTestCommand`
+  → hands to `MainViewModel.StopStream`, `EndTestSilently` (idempotent, called on any stop/
+  rollback). Fully testable — takes `YouTubeStreamService` + `YouTubeChatService` via ctor.
+- **`Services/YouTubeStreamService.InsertChatMessageAsync(liveChatId, text)`** —
+  `POST liveChat/messages?part=snippet`; returns string error or null; never throws.
+- **`Services/YouTubeChatService.InjectSimulatedMessage(ChatMessage)`** — raises `MessageReceived`,
+  the exact seam the real poll uses, so simulations flow through the whole overlay pipeline;
+  marked `ChatMessage.IsSimulated`.
+- **`ViewModels/MainViewModel.*`** — `IsTestStream` (internal setter, test seam like `IsRecording`);
+  `BeginTestStream()` → the shared `StartStreamingSession(alsoRecord:false)` extracted from
+  `BeginGoLive` (no dialog — a Test needs no confirmation, every broadcast is already private; no
+  `BroadcastForm.CaptureGoLive` "last live" stamp; no recording). `StopStream` clears the face and
+  forgets the drawer session. `EndButtonText` = "End Test" while in a test. Gold top bar + glow
+  (`#9c6f1c`) identify a rehearsal vs the live red.
+- **Drawer exclusivity** (this task): opening TEST collapses Stream Settings + YPP and vice versa
+  (wired in `MainViewModel.Ypp.cs`).
+
+## Good Dog — ONE integration test
+
+`ytLive.Tests/TestStreamTests.cs` — one `[Fact]`, two sections:
+1. **Coordinator (no network, `RecordingHandler`-faked HTTP):** idle → `BeginTest` opens the dock
+   + enables chat; Mock Chat Input emits the insert (POST body asserted for the liveChatId +
+   messageText); Subscriber/New Member/Super Chat simulations arrive through `MessageReceived`
+   marked `IsSimulated` with the right shapes (member level, `$5.00` Super Chat, plain subscriber
+   row); End hands back to the app; `EndTestSilently` clears.
+2. **Real window (temp DB):** TEST tab/drawer exist, three-way drawer exclusivity, Test button
+   gate follows sign-in deterministically.
+
+## Follow-ups (NOT in this task)
+
+- Real stinger/TTS alert widgets → TASK 3 items 16/17/20.
+- Test-mode health-panel depth (per-broadcast status inside the drawer) if ever wanted.