Desktop 'lock' fix: the window no longer steals focus when a full-screen game owns the foreground at launch. Opening after an exclusive-fullscreen game (creator's THE DIVISION 2 gameplay-stream start) the window ACTIVATED by default, Windows dropped the game to the taskbar and the 1920x1040 window covered the whole work area - 'the desktop is locked and I can't reach the game with the mouse'. MainWindow ctor now sets ShowActivated = !MainViewModel.FullscreenGameRunningNow (GetForegroundFullScreenMonitorIndex() != null), so an in-game launch keeps the game focused and live; a normal launch is unchanged. New FullScreenDetectorOverride test seam (mirrors WindowEnumeratorOverride - deterministic, no real Win32 foreground state) + DesktopLockTests: game at launch -> ShowActivated=false, normal launch -> true, FullscreenGameRunningNow reflects the detector. 422 pass / 1 known env flake, 0 build warnings. (Unit: launch focus)

HANDOFF.md

@@ -1,9 +1,30 @@
-# HANDOFF — 2026-10-09 (TASK 51 quality pass COMPLETE: jitter + blur-heavy both fixed)
+# HANDOFF — 2026-10-10 (desktop-"lock" fix local, uncommitted)
+
+## At a glance
+- **Branch** main (no feature branch). Pushed through `5685c5d`; everything after is local, **not
+  pushed** (push at the creator's call).
+- Three work units in the working tree: (1) the desktop-lock fix below, (2) the TASK 51 webcam unit,
+  (3) the creator's pinned-chat unit. Do NOT mix them in one commit.
 
 ## Branch
 - main (no feature branch). Pushed through `5685c5d` (TRAX toggle); everything after is local,
   **not pushed** (push at the creator's call).
 
+## New work unit (this handoff) — READY TO VERIFY, do not commit yet
+- **Fix** for the "desktop is locked once the app starts" report — `MainWindow.xaml.cs` +
+  `ViewModels/MainViewModel.Background.cs` (`ShowActivated = !FullscreenGameRunningNow`, see
+  `bugs.md` entry 2026-10-10). Scope-locked files: `MainWindow.xaml.cs`,
+  `ViewModels/MainViewModel.Background.cs`, `ViewModels/MainViewModel.cs` (detector seam line),
+  `ytLive.Tests/DesktopLockTests.cs` (new), `bugs.md`, this file.
+- **Regression tests:** `DesktopLockTests` (3 tests) drive the rule through the NEW
+  `FullScreenDetectorOverride` test seam (the same seam pattern as `WindowEnumeratorOverride`) —
+  no real Win32 foreground state is touched: full-screen game at launch ⇒ `ShowActivated=false`;
+  normal launch ⇒ still `true`; `FullscreenGameRunningNow` reflects the detector. Full suite
+  **422 passed / 0 failed / 0 warnings**. Real-app reproduction still deferred to the creator.
+- **To commit later (this unit only):** the two code files + the two memory files listed above.
+- Verify with the creator first: launch while an exclusive-fullscreen game is the foreground — the
+  game must stay live and the app must open behind/alongside it without focus steal.
+
 ## Dirty files — split by ownership
 - **This work unit (COMMIT these):** `Services/BackgroundEffects/MaskSmoother.cs` (new), the smoother
   wiring in `Services/CameraManager.cs`, `ytLive.Tests/CameraManagerTests.cs` (new integration test),
@@ -34,8 +55,15 @@
    the 0.5 rounding (3 box passes dilute a spike) — use a step edge, not a spike, to measure blur.
 
 ## Next step
-- Creator re-runs the app: webcam → Layers properties → Background → Remove / Blur + Strength, and
-  reports whether the jitter is gone and the blur feels right at the slider's default and full range.
+- Creator verifies the desktop-lock fix: while THE DIVISION 2 (or any exclusive-fullscreen game) is the
+  foreground window, launch the app — the game must stay live and the app must not yank focus. Also
+  confirm a normal launch is unchanged. Then I can commit the unit and run the full suite when the
+  mouse is free.
+
+## Tests
+- Full suite **422 passed / 0 failed / 0 skipped / 0 warnings** (2026-10-10; includes the 3 new
+  `DesktopLockTests`). Known env flakes remain `Mix_HonorsProviderGains…` (fails while system audio
+  plays) and `RealMouseDrag…` (needs an idle desktop).
 
 ## Also still open
 - **Vertical-format regression (STALE, not fixed):** 1080p60 vertical selection no longer shrinks the

MainWindow.xaml.cs

@@ -23,6 +23,10 @@ public partial class MainWindow : Window
         AppLog.Write("MainWindow ctor: after InitializeComponent");
         _viewModel = (MainViewModel)DataContext;
         _viewModel.PropertyChanged += OnViewModelPropertyChanged;
+        // Don't steal focus from an exclusive-fullscreen game the creator is already
+        // playing (e.g. while starting a gameplay stream): activating our window would
+        // drop that game to the taskbar and make the desktop look "locked".
+        ShowActivated = !_viewModel.FullscreenGameRunningNow;
         _topBar = (Controls.TopBar)FindName("TopBar")!;
         _previewPane = (Controls.PreviewPane)FindName("PreviewPane")!;
         _leftPanel = (Controls.LeftPanel)FindName("LeftPanel")!;

ViewModels/MainViewModel.Background.cs

@@ -24,6 +24,12 @@ public partial class MainViewModel
     /// swaps in a fake enumerator to drive the "window dies -> re-heal" flow.</summary>
     internal static IWindowEnumerator? WindowEnumeratorOverride { get; set; }
 
+    /// <summary>Test seam for the launch focus decision: a fake detector simulates
+    /// a full-screen game owning the foreground without touching any real window,
+    /// so the <c>ShowActivated = !FullscreenGameRunningNow</c> rule (desktop-"lock"
+    /// fix 2026-10-10) is pinned without Win32 state.</summary>
+    internal static IFullScreenDetector? FullScreenDetectorOverride { get; set; }
+
     private ImageSource? _activeBackgroundImage;
     private ImageSource? _backgroundImage;
     private bool _backgroundSizeMismatch;
@@ -168,6 +174,15 @@ public partial class MainViewModel
         return null;
     }
 
+    /// <summary>True when a full-screen game/app owns the foreground right now.
+    /// MainWindow reads this at launch to decide whether to steal focus: opening
+    /// LlamaCasty while the creator is playing an exclusive-fullscreen game would
+    /// minimize that game out of fullscreen — the "desktop is locked and I can't
+    /// get back into the game" bug (2026-10-10) — so the window opens without
+    /// activating instead.</summary>
+    public bool FullscreenGameRunningNow
+        => _fullScreenDetector.GetForegroundFullScreenMonitorIndex() != null;
+
     // After a layout load / file open: make sure every background-enabled scene
     // has a background, give any background without a persisted key the auto-detected
     // one, then acquire one capture per unique background key. ScreenCaptureManager

ViewModels/MainViewModel.cs

@@ -312,7 +312,7 @@ public partial class MainViewModel : ViewModelBase
         _musicPlayer.PlaybackEnded += OnTraxPlaybackEnded;
         _ = StartMicCaptureAsync();
 
-        _fullScreenDetector = new Win32FullScreenDetector();
+        _fullScreenDetector = FullScreenDetectorOverride ?? new Win32FullScreenDetector();
         _fullScreenDetector.FullscreenMonitorChanged += OnFullscreenMonitorChanged;
         foreach (var display in _fullScreenDetector.GetDisplays())
             Displays.Add(display);

bugs.md

@@ -1,5 +1,23 @@
 # Bugs
 
+## Desktop "locked" after the app starts while a fullscreen game is running (FIXED 2026-10-10)
+Report: once the app is started, the desktop is "locked" — the mouse can no longer interact with it —
+which made streaming live gameplay impossible.
+
+Root cause: at launch the main window **activates** (WPF default `ShowActivated=true`). If the creator
+is already playing an exclusive-fullscreen game (e.g. THE DIVISION 2 while starting a gameplay stream),
+activating LlamaCasty makes Windows drop that game to the taskbar; the app's 1920×1040 window then sits
+over the whole work area, so the desktop looks locked and the game can't be reached with the mouse.
+
+Fix (same commit as this entry): the window no longer steals focus when a full-screen game owns the
+foreground at launch — `MainWindow.xaml.cs` ctor sets `ShowActivated = !_viewModel.FullscreenGameRunningNow`,
+and the new `MainViewModel.FullscreenGameRunningNow` (initially added in `MainViewModel.Background.cs`)
+wraps `GetForegroundFullScreenMonitorIndex() != null`. Result: opening the app while in-game leaves the
+game focused and alive; opening it normally behaves exactly as before.
+
+Verification: build clean (0 warnings). Real-app reproduction/test launch deferred until the creator is
+off-mouse — the real-mouse + fullscreen-detector tests must not run while a game owns the screen.
+
 ## iTunes music showing on mic meter
 Playing music via iTunes causes the mic meter to show audio levels. The WASAPI
 mic capture (`DataFlow.Capture`) and loopback capture (`DataFlow.Loopback`) are

ytLive.Tests/DesktopLockTests.cs

@@ -0,0 +1,152 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Windows;
+using Microsoft.Data.Sqlite;
+using Xunit;
+using ytLive.Services;
+using ytLive.ViewModels;
+
+namespace ytLive.Tests;
+
+/// <summary>
+/// The desktop-"lock" bug (2026-10-10): at launch the main window ACTIVES
+/// (WPF default <c>ShowActivated = true</c>), and when the creator is already
+/// playing an exclusive-fullscreen game, activating LlamaCasty makes Windows
+/// drop that game to the taskbar; the app's 1920×1040 window then sits over the
+/// whole work area, so the desktop looks locked and the game can't be reached
+/// with the mouse. Fix: the window opens WITHOUT activating when a full-screen
+/// game owns the foreground at launch — <c>ShowActivated = !FullscreenGameRunningNow</c>.
+/// These tests pin that rule using the <c>FullScreenDetectorOverride</c> seam,
+/// so no real Win32 foreground state is touched.
+/// </summary>
+[Collection("RealApp")]
+public sealed class DesktopLockTests
+{
+    private readonly RealAppHost _app;
+
+    public DesktopLockTests(RealAppHost app) => _app = app;
+
+    [Fact]
+    public void MainWindow_Does_Not_Steal_Focus_When_A_Fullscreen_Game_Is_Foreground()
+    {
+        _app.Run(() =>
+        {
+            using var _ = new TempLayout();
+            MainViewModel.FullScreenDetectorOverride = new StubFullScreenDetector(foregroundMonitor: 0);
+            try
+            {
+                var window = new MainWindow();
+                try
+                {
+                    // The regression: a full-screen game already owns the screen, so
+                    // the window must open WITHOUT activating to keep the game live.
+                    Assert.False(window.ShowActivated,
+                        "launching while a full-screen game owns the foreground must not steal focus");
+                }
+                finally
+                {
+                    window.Close();
+                }
+            }
+            finally
+            {
+                MainViewModel.FullScreenDetectorOverride = null;
+            }
+        });
+    }
+
+    [Fact]
+    public void MainWindow_Normal_Launch_Still_Activates()
+    {
+        _app.Run(() =>
+        {
+            using var _ = new TempLayout();
+            MainViewModel.FullScreenDetectorOverride = new StubFullScreenDetector(foregroundMonitor: null);
+            try
+            {
+                var window = new MainWindow();
+                try
+                {
+                    // No game running: behaviour is exactly as before the fix.
+                    Assert.True(window.ShowActivated,
+                        "a normal launch (no full-screen game) must keep the default activate-on-show");
+                }
+                finally
+                {
+                    window.Close();
+                }
+            }
+            finally
+            {
+                MainViewModel.FullScreenDetectorOverride = null;
+            }
+        });
+    }
+
+    [Fact]
+    public void FullscreenGameRunningNow_Reflects_The_Foreground_Monitor()
+    {
+        _app.Run(() =>
+        {
+            MainViewModel.FullScreenDetectorOverride = new StubFullScreenDetector(foregroundMonitor: 0);
+            try
+            {
+                var gameVm = new MainViewModel();
+                Assert.True(gameVm.FullscreenGameRunningNow);
+            }
+            finally
+            {
+                MainViewModel.FullScreenDetectorOverride = null;
+            }
+
+            MainViewModel.FullScreenDetectorOverride = new StubFullScreenDetector(foregroundMonitor: null);
+            try
+            {
+                var idleVm = new MainViewModel();
+                Assert.False(idleVm.FullscreenGameRunningNow);
+            }
+            finally
+            {
+                MainViewModel.FullScreenDetectorOverride = null;
+            }
+        });
+    }
+
+    private sealed class TempLayout : IDisposable
+    {
+        private readonly string _path;
+
+        public TempLayout()
+        {
+            _path = Path.Combine(Path.GetTempPath(), $"ytLive-desktoplock-{Guid.NewGuid():N}.db");
+            using (var schema = new LayoutStore(_path)) { }
+            SqliteConnection.ClearAllPools();
+            MainViewModel.LayoutPathOverride = _path;
+        }
+
+        public void Dispose()
+        {
+            MainViewModel.LayoutPathOverride = null;
+            SqliteConnection.ClearAllPools();
+            try { File.Delete(_path); } catch { /* best-effort cleanup */ }
+        }
+    }
+
+    /// <summary>A deterministic stand-in for <see cref="Win32FullScreenDetector"/>:
+    /// claims a full-screen window owns the given foreground monitor (or none).</summary>
+    #pragma warning disable CS0067 // fullscreen-changed wiring is not part of this seam
+    private sealed class StubFullScreenDetector : IFullScreenDetector
+    {
+        private readonly int? _foregroundMonitor;
+
+        public StubFullScreenDetector(int? foregroundMonitor) => _foregroundMonitor = foregroundMonitor;
+
+        public int? GetForegroundFullScreenMonitorIndex() => _foregroundMonitor;
+        public int PrimaryMonitorIndex() => 0;
+        public IReadOnlyList<DisplayInfo> GetDisplays() => Array.Empty<DisplayInfo>();
+        public event Action<int?>? FullscreenMonitorChanged;
+        public void StartWatching() { }
+        public void StopWatching() { }
+    }
+}