feat(ui): add current-launch logs tab

Add Live Chat and Logs tabs to the non-edit left panel. Expose a bounded process-local AppLog feed so the newest messages appear first without importing earlier startup.log contents or changing file logging.

Ref: https://obsproject.com/forum/resources/understanding-obs-studio-log.473

Helpers/AppLog.cs

@@ -12,6 +12,7 @@ public static class AppLog
 {
     /// <summary>The cap for the live log file. Past this, it rolls to <c>startup.1.log</c>.</summary>
     private const long DefaultMaxBytes = 5 * 1024 * 1024;
+    private const int CurrentLaunchEntryLimit = 500;
 
     /// <summary>How many rolled copies to keep (startup.1.log, startup.2.log, …).</summary>
     private const int RetainedFiles = 1;
@@ -20,6 +21,8 @@ public static class AppLog
         InstanceProfile.DataRoot, "startup.log");
 
     private static readonly object Gate = new();
+    private static readonly List<AppLogEntry> CurrentLaunchEntries = new();
+    private static long _nextSequence;
 
     /// <summary>Test seam: point the log somewhere else. Null = the real profile's log.</summary>
     internal static string? PathOverride { get; set; }
@@ -29,16 +32,29 @@ public static class AppLog
 
     private static string LogPath => PathOverride ?? DefaultLogPath;
 
+    internal static IReadOnlyList<AppLogEntry> SnapshotCurrentLaunch()
+    {
+        lock (Gate)
+            return CurrentLaunchEntries.ToArray();
+    }
+
     public static void Write(string message)
     {
         try
         {
             lock (Gate)
             {
+                var entry = new AppLogEntry(
+                    ++_nextSequence,
+                    $"{DateTime.Now:yyyy-MM-dd HH:mm:ss.fff} {message}");
+                CurrentLaunchEntries.Add(entry);
+                if (CurrentLaunchEntries.Count > CurrentLaunchEntryLimit)
+                    CurrentLaunchEntries.RemoveAt(0);
+
                 var path = LogPath;
                 Directory.CreateDirectory(Path.GetDirectoryName(path)!);
                 LogRotation.RollIfNeeded(path, MaxBytes, RetainedFiles);
-                File.AppendAllText(path, $"{DateTime.Now:yyyy-MM-dd HH:mm:ss.fff} {message}{Environment.NewLine}");
+                File.AppendAllText(path, $"{entry.Text}{Environment.NewLine}");
             }
         }
         catch
@@ -52,3 +68,5 @@ public static class AppLog
         Write($"{message}: {exception}");
     }
 }
+
+public sealed record AppLogEntry(long Sequence, string Text);

Helpers/index.md

@@ -6,7 +6,7 @@ Cross-cutting utilities. See [`schema.md`](../schema.md) for the memory-map conv
 |------|---------|
 | `ViewModelBase.cs` | `INotifyPropertyChanged` + `SetProperty<T>()` — base for all ViewModels |
 | `RelayCommand.cs` | `ICommand` implementation for all button actions |
-| `AppLog.cs` | File logger to `%APPDATA%\ytLlive\startup.log`; startup checkpoints + unhandled-exception capture (the crash this map is named for). Size-capped: rolls to `startup.1.log` at 5 MB (TASK 55) |
+| `AppLog.cs` | File logger to `%APPDATA%\ytLlive\startup.log`; startup checkpoints + unhandled-exception capture. Size-capped: rolls to `startup.1.log` at 5 MB (TASK 55). Also keeps the newest 500 formatted entries in a process-local buffer for the Logs tab; it never loads prior-launch file contents |
 | `LogRotation.cs` | The size-capped-rotation policy as a pure function over a path: roll `startup.log` → `startup.1.log` when it passes the cap, keeping N rolled copies. Separate from `AppLog` so the logger's 156-call-site surface never changes and the rule is testable alone (TASK 55) |
 | `FocusPreservingListBox.cs` | `ListBox` subclass that keeps selection/focus coherent when the selected item is deleted; `IsSelectable` predicate skips hidden scenes; drag-reorder guard |
 | `OAuthCredentials.cs` | Baked-in Google OAuth client ID/secret (desktop app; loopback callback) |