fix(stream): health poll crashed on every start — parse the real healthStatus object shape

startup.log 2026-09-22 (via the user's run of the new build): every session
start logged 'Stream health poll failed: The requested operation requires an
element of type String, but the target element has type Object'.

Root cause: GetStreamHealthAsync did status.healthStatus.GetString(), but the
real API nests it as status.healthStatus = {status, lastUpdateTimeSeconds,
configurationIssues[]} — an OBJECT, per the liveStreams reference
https://developers.google.com/youtube/v3/live/docs/liveStreams (checked the
docs before fixing, per derivative-work rule). Our flat-string fixture was the
wrong assumption since TASK 9; the report-by-exception health banner had been
silently dead.

Fix: read the nested healthStatus.status + nested configurationIssues[], tolerating
the legacy flat-string shape so nothing else breaks. Tests flipped to the real
object shape (the Good Dog for this change). Full suite 315/315, build 0 warnings.

Also recorded in MyMistakes.md (API-shape recipe) and ai.md/Services index. End-of-session
transition(complete) 403 invalidTransition (enableAutoStop fallback) observed on all three
2026-09-22 stops — separate racy-design issue, carried, not in this change.

ai.md

@@ -208,7 +208,7 @@ The AI hallucinated through multiple commits that night on background/scene prop
 
 - `Helpers/OAuthCredentials.cs` contains the real ClientId/ClientSecret. Auth is complete and the session **persists via Windows DPAPI** (`Helpers/TokenStore.cs` → `%APPDATA%\ytLlive\ytLlive.auth`, CurrentUser scope), reloaded best-effort at startup with a proactive refresh of a near-expiry access token. Sign-in/Change Account lives **inside the Start Stream dialog** (two-state flow — no separate Connect button). Sign-out is **explicit only** (Logout / Change Account → `SignOutYouTubeAsync`): `StopStream()` does NOT clear the session — TASK 18's 2026-08-29 reversal ("stopping a recording leaves the creator signed in") — the older "graceful End signs out" line here was stale and is corrected against the code (2026-09-01). `YouTubeAuthService` takes an optional `HttpClient` + `sessionChanged` callback (test seam + save hook; services are still constructed in `MainViewModel`)
 - Scene/source/asset layout + the social bar persist (SQLite, schema v8); the OAuth session persists (DPAPI); the paid-unlock state persists (LayoutStore Settings table — `LicenseKey`/`LicenseValidatedAt`/`IsPremium`, 14-day offline grace)
-- `YouTubeStreamService` manages the **variable reusable stream** (shipped 2026-08-16): `GetOrCreateReusableStreamAsync` lists `liveStreams?mine=true` and reuses the existing `cdn.isReusable` stream, creating it only on first use (`resolution=variable`, `frameRate=variable`); the stream is cached via `LayoutStore` (`SaveReusableStream`/`LoadReusableStream`, Settings table) and bound at broadcast insert (`boundStreamId`). Health (shipped 2026-08-16): `GetStreamHealthAsync(streamId)` polls `liveStreams?part=status` for `healthStatus` + `configurationIssues[]` → `StreamHealth`; banner decision in pure `StreamHealthReporter`
+- `YouTubeStreamService` manages the **variable reusable stream** (shipped 2026-08-16): `GetOrCreateReusableStreamAsync` lists `liveStreams?mine=true` and reuses the existing `cdn.isReusable` stream, creating it only on first use (`resolution=variable`, `frameRate=variable`); the stream is cached via `LayoutStore` (`SaveReusableStream`/`LoadReusableStream`, Settings table) and bound at broadcast insert (`boundStreamId`). Health (shipped 2026-08-16): `GetStreamHealthAsync(streamId)` polls `liveStreams?part=status` for `healthStatus` + `configurationIssues[]` → `StreamHealth`; the real API nests them under `status.healthStatus = {status, lastUpdateTimeSeconds, configurationIssues[]}` — the parse accepts that object shape and the legacy flat-string shape (fix 2026-09-22: the object shape crashed every poll with `requires an element of type 'String'`); banner decision in pure `StreamHealthReporter`
 - Webcam capture is shipped (milestone 1); the live desktop/game backdrop is shipped (ship task #1); **the output compositor (TASK 4 ship step 1) is SHIPPED**, **the FFmpeg locator (TASK 4 ship step 2) is SHIPPED**, **the encoder + RTMP push (TASK 4 ship step 3) is SHIPPED**, **WASAPI audio capture (TASK 4 ship step 4) is SHIPPED**, **frame-pipeline wiring (TASK 4 ship step 5) is SHIPPED**, **health stats (TASK 4 ship step 6) is SHIPPED**, **one-click go-live + private-only enforcement (TASK 4 ship step 7) is SHIPPED** — TASK 4 (RTMP Ingest) is fully done; full plan in `TASKS.md`
 - `StreamConfig` defaults (`TargetBitrate=6000`, `Resolution="1920x1080"`) are stale — the live dropdown drives `StreamHealth.CurrentBitrate`/`FPS` instead
 - **v1 task queue (2026-08-19):** tasks 19-23 added for v1 feature completeness; TASK 3.18 (chat box) shipped; TASK 16 (infinity display) shipped; TASK 10 (Polar billing) shipped — steps 1-7 (Velopack bootstrap, PolarLicenseService, license entry UI, LayoutStore entitlement, BrandFlash toggle, startup re-validation, PremiumUrl wired); Velopack update URL pending:
@@ -1520,7 +1520,11 @@ These are the hard facts behind every decision. Full list in `TASKS.md`.
   on `configurationIssues[]` with `warning`/`error` severity. The decision is the pure
   `Services/StreamHealthReporter.BannerFor` (null text = no banner; error beats warning). The VM polls
   every **30s while live** (`DispatcherTimer` `_healthPollTimer`, first poll right after go-live) and
-  clears on End via `ResetHealth`; poll failures log only. UI = a full-width banner strip under the
+  clears on End via `ResetHealth`; poll failures log only. **Parsing (fix 2026-09-22):** the real API
+  nests `status.healthStatus = {status, lastUpdateTimeSeconds, configurationIssues[]}` — reading it as
+  a string crashed every poll (`requires an element of type 'String'`, seen 2026-09-22 on both test
+  sessions); the parse now reads the nested `.status`/`configurationIssues` and tolerates the old
+  flat-string shape. UI = a full-width banner strip under the
   top bar, `HealthIssueBanner` text + `HealthIssueBackground` (amber `#b8860b` warning / dark red
   `#8f1f1f` error), hidden by `NotNullToVis`. The design's bottom-strip YouTube logo + green/red dot
   (clickable → dialog) is still queued.