fix(stream): TEST-tab chat — resolve liveChatId from snippet, poll until the broadcast is live

The open creator report ('I still cannot post a chat message in the TEST tab',
feedback 'Chat polling couldn't start — Mock Chat Input is disabled') was a single
cause: the liveChatId never resolved. Two YouTube API facts:
1. The id lives in snippet.liveChatId — contentDetails has no such property
   (TASK 44 read part=contentDetails: could never resolve).
   https://developers.google.com/youtube/v3/live/docs/liveBroadcasts
2. It only exists once the broadcast is LIVE — the official sample lists
   broadcastStatus=active, and our fetch ran before the frame pump pushed RTMP
   (enableAutoStart flips ready→live). A ready-state list legitimately returns
   no id.
   https://github.com/youtube/api-samples/blob/master/java/src/main/java/com/google/api/services/samples/youtube/cmdline/live/GetLiveChatId.java

Fix: GetBroadcastLiveChatIdAsync reads part=snippet and polls with a bounded
retry (10x/2s); PrepareAndStartLiveAsync starts the frame pump FIRST, then
resolves the id. Chat stays non-fatal. Docs ai.md/TASKS.md/HANDOFF.md +
MyMistakes recipe updated same commit. TASK 44.

Good Dog: ONE integration test (GetBroadcastLiveChatIdAsync_Polls_Snippet_...
) drives a broadcast that gains its id mid-retry and asserts every request used
part=snippet. Gate: clean build 0 warnings, vstest 318/318.

HANDOFF.md

@@ -1,52 +1,41 @@
-# HANDOFF — 2026-09-24 (TASK 43 shipped: native events & alerts — creator said "go")
+# HANDOFF — 2026-09-25 (TASK 44 shipped: TEST-tab chat fix — liveChatId now resolves)
 
 ## Branch / Commit State
 
-`main` HEAD = new commit for TASK 43 (native events & six-animation alert box); previous:
-`3a4e17c` (account zone world-independent), `cb75066` (YPP 403), `d72949e` (top-bar feedback),
-`ac6e67a` (end close-out). Repo is ~10 commits ahead of pushed `197ee81` — **push is the
-creator's call** (sub-milestone decision, not per-commit).
+`main` HEAD = new commit for TASK 44 (TEST-tab chat fix); previous: TASK 43 commit (native
+events & alerts), `ac6e67a` (end close-out). Repo is ~11 commits ahead of pushed `197ee81` —
+**push is the creator's call** (sub-milestone decision, not per-commit).
 
 **Working tree CLEAN after this unit's commit.**
 
-## ⚠️ The unit that just shipped (this turn, creator said "go")
+## ⚠️ The unit that just shipped (the open TEST-tab chat report, diagnosed + fixed)
 
-The creator asked (2026-09-23) whether the app could use **native YouTube events instead of
-StreamElements**. Research pinned the API facts; creator rulings locked the product shape. One
-combined work unit ("go"), task filed as **TASK 43** (`TASKS/task-43-native-alerts.md`):
+The HANDOFF-open creator report — *"I still cannot post a chat message in the TEST tab"* —
+is **RESOLVED** (one cause, one scoped unit, TASK 44 in `TASKS/task-44-test-chat-fix.md`):
 
-1. **Chat parity half** — `YouTubeChatService` now decodes **all six** `liveChat/messages`
-   event types into `ChatMessage.Kind` (the four previously-empty event rows are real now) and
-   re-arms its poll on the server's `pollingIntervalMillis` (streamList semantics; clamp
-   1000–6000ms, `maxResults=2000`).
-2. **Alerts half** — new **`SourceType.AlertBox`** ("Stream Alerts", one per layout,
-   `CanAddAlerts` gate mirroring chat): an OBS-style celebration zone, idle = transparent.
-   `Services/AlertRenderer.cs` draws **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), each card carrying the "made with
-   LlamaCasty!" brand line (free product placement per broadcast). `Services/AlertOverlayLayer.cs`
-   is a true component (Commit-G pattern): queue (cap 10) + 33ms ticker + cache-first
-   `RenderFrame` + `UpdatePreview`; **`Advance(double)` = deterministic test clock**.
-3. **Creator rulings baked in:** no menus/polls (asked once, held); free-sub mention = chat row
-   only, **no sub alert** (YouTube emits none); **no viewer count** (vetoed — demotivating,
-   weaponizable); six events = six unique animations, not a recolored template.
+- **The feedback line** "Chat polling couldn't start — Mock Chat Input is disabled" is
+  `TestSessionViewModel.BeginTest` running with a **null liveChatId**.
+- **Root cause (two API facts, cited in commit + MyMistakes):** (1) `liveChatId` lives in
+  **`snippet.liveChatId`** — `contentDetails` has no such property, and the old code read
+  `part=contentDetails` (can NEVER resolve); (2) YouTube only populates it once the broadcast
+  is **live** (official `GetLiveChatId.java` lists `broadcastStatus=active`), and the fetch
+  ran before the frame pump pushed RTMP (enableAutoStart flips ready→live).
+- **Fix:** `GetBroadcastLiveChatIdAsync(broadcastId, maxAttempts=10, delayMs=2000)` now reads
+  `part=snippet` and polls with a bounded retry; `PrepareAndStartLiveAsync` starts the frame
+  pump FIRST, then resolves the id. Chat stays non-fatal. TEST drawer wiring unchanged
+  (`BeginTest` opens the dock once the id resolves → Mock Chat Input becomes sendable).
 
-**Good Dog:** `ytLive.Tests/AlertLayerTests.cs` (RealApp STA, real WPF raster) — ParsePage
-classifies all six kinds + cadence fields; playback never enqueues a `None` (sub-mention) row,
-plays six pairwise-distinct moving frames, drains to idle. **Gate: clean build 0 warnings,
-316/317** — the ONE failure (`LayerReorderPersistenceTests.RealMouseDrag…`) repros on the CLEAN
-tree (proved via `git stash` + rebuild + isolated run): a real-mouse-drag test that no-ops while
-a game/fullscreen window steals the mouse (the HANDOFF-documented environmental class).
-**NOT a regression — do not chase it in-app; close games and rerun if in doubt.**
+**Good Dog:** ONE integration test in `YouTubeStreamServiceTests.cs`
+(`GetBroadcastLiveChatIdAsync_Polls_Snippet_Until_Id_Appears`) — a fake broadcast that starts
+without a liveChatId and gains it on a later poll; asserts the retry resolves it, polled ≥3x,
+and every request asked for snippet (never contentDetails). **Gate: clean build 0 warnings,
+full vstest 318/318 passed** (the LayerReorder real-mouse-drag test passed this run too).
 
 ## Follow-ups queued (NOT done in this unit)
 
-- **Creator report still open — not yet diagnosed:** "I still cannot post a chat message in the
-  TEST tab." The TEST drawer's Mock Chat Input posts a REAL `liveChat/messages.insert`; the fix
-  needs its own scoped unit.
 - **TASK 3 item 20 persistence half** — the canonical `RewardEvents` SQLite table +
-  `superChatEvents.list` (30-day) backfill + session-report rollup (the shipped alert path parses
-  events to `ChatMessage` in memory; the report reads that table once it exists).
+  `superChatEvents.list` (30-day) backfill + session-report rollup (events still parse to
+  `ChatMessage` in memory only).
 - TASK 3 item 16 (Text source) still open; TASK 40 units A/C/D queued; TASK 32–36 queued.
 
 ## Around the task (carried facts)
@@ -58,20 +47,19 @@ a game/fullscreen window steals the mouse (the HANDOFF-documented environmental
   must become one-time before launch. `MARCOM.md`/`MONETIZATION.md` gitignored — never commit.
 - Latent bug the YPP 403 masked: statistics are JSON **strings** — always the ValueKind-first
   `ReadInt64` (MyMistakes recipe), never `GetInt64`.
-- New facts recorded: the chat feed IS the event feed (six types, no sub event); streamList is a
-  connection-semantics description of that same endpoint (pollingIntervalMillis drives cadence).
+- **API fact (TASK 44):** a liveChatId fetch at insert time (lifecycleStatus `ready`) returns
+  nothing by design — missing liveChatId ≈ "broadcast not live yet", not an auth failure,
+  until ~20s post push. Debug with that lens.
 - Every committed change needs a **close + relaunch** of the running app to be seen — running
   builds are live; verify.sh can't run while the exe is locked.
 
 ## Next step
 
-1. **Creator verifies the alerts unit on the next run**: Add → Stream Alerts, then (Test Stream
-   drawer) Simulated Super Chat / New Member — confirm the zone stays transparent at idle and each
-   event plays its own animation on the canvas and preview; a real Super Chat during the next live
-   run confirms the real path.
-2. Push decision is the creator's (repo ~10 ahead). If pushed, note the commit id in this file.
-3. When scoped: diagnose the TEST-tab chat posting report ("I still cannot post a chat message in
-   the TEST tab") as its own Good-Dog unit.
+1. **Creator verifies the TEST-tab chat fix on the next run**: Test Stream → the drawer should
+   open with a liveChatId line and Mock Chat Input enabled ~as soon as the broadcast goes live;
+   send a message and confirm it round-trips through the ~2s poll and renders on the overlay.
+2. Push decision is the creator's (repo ~11 ahead). If pushed, note the commit id in this file.
+3. When scoped: TASK 3 item 20 (RewardEvents persistence half) draws next.
 
 ## Critical working rules (unchanged, still binding)