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.

ytLive.Tests/YouTubeStreamServiceTests.cs

@@ -159,17 +159,22 @@ public class YouTubeStreamServiceTests
         Assert.Empty(handler.Requests); // never reached the API
     }
 
-    // TASK 5 item 3: liveStreams.status — healthStatus + configurationIssues[]
-    // parsed into the report-by-exception surface.
+    // TASK 5 item 3: liveStreams.status — status.healthStatus = {status,
+    // configurationIssues[]} (the REAL API shape — nested object, not a string;
+    // the flat-string shape was our own wrong fixture) parsed into the
+    // report-by-exception surface. This fixture is what a live test/real stream
+    // actually returns — it used to crash the poll with
+    // "requires an element of type 'String'" (2026-09-22 log, two sessions).
     [Fact]
     public async Task GetStreamHealthAsync_Parses_Status_And_Issue_Severities()
     {
         var handler = new RecordingHandler
         {
             ResponseBody = """
-                {"items":[{"status":{"healthStatus":"bad","configurationIssues":[
+                {"items":[{"status":{"healthStatus":{"status":"bad","lastUpdateTimeSeconds":1748000000,
+                    "configurationIssues":[
                     {"type":"bitrateHigh","severity":"error"},
-                    {"type":"reconnect","severity":"warning"}]}}]}
+                    {"type":"reconnect","severity":"warning"}]}}}]}
                 """
         };
         var service = new YouTubeStreamService(CreateAuthed(), new HttpClient(handler));
@@ -188,7 +193,7 @@ public class YouTubeStreamServiceTests
     [Fact]
     public async Task GetStreamHealthAsync_Good_Health_Yields_No_Issues()
     {
-        var handler = new RecordingHandler { ResponseBody = """{"items":[{"status":{"healthStatus":"good"}}]}""" };
+        var handler = new RecordingHandler { ResponseBody = """{"items":[{"status":{"healthStatus":{"status":"good"}}}]}""" };
         var service = new YouTubeStreamService(CreateAuthed(), new HttpClient(handler));
 
         var health = await service.GetStreamHealthAsync("S456");
@@ -218,7 +223,7 @@ public class YouTubeStreamServiceTests
     {
         var handler = new RecordingHandler
         {
-            ResponseBody = """{"items":[{"status":{"healthStatus":"good"}}]}"""
+            ResponseBody = """{"items":[{"status":{"healthStatus":{"status":"good"}}}]}"""
         };
         var service = new YouTubeStreamService(CreateAuthed(), new HttpClient(handler));
 
@@ -228,8 +233,9 @@ public class YouTubeStreamServiceTests
         Assert.Null(StreamHealthReporter.BannerFor(healthy!.ConfigurationIssues).Text);
 
         handler.ResponseBody = """
-            {"items":[{"status":{"healthStatus":"bad","configurationIssues":[
-                {"type":"bitrateHigh","severity":"error"}]}}]}
+            {"items":[{"status":{"healthStatus":{"status":"bad",
+                "configurationIssues":[
+                {"type":"bitrateHigh","severity":"error"}]}}}]}
             """;
         var degraded = await service.GetStreamHealthAsync("S456");
         Assert.Equal("bad", degraded?.HealthStatus);