feat: log pause/resume events to changes.log with reason + foreground process

Author: carterscode

README.md

@@ -254,7 +254,7 @@ Fields:
 | Field | Meaning |
 |---|---|
 | **timestamp** | Local time of the apply |
-| **source** | `manual` (you clicked Apply) or `auto` (silent auto-apply during a poll tick) |
+| **source** | `manual` (you clicked Apply) · `auto` (silent auto-apply during a poll tick) · `ui` (preference toggle in Settings) · `pause` (polling paused/resumed for fullscreen, benchmark, or manual pause) |
 | **STATUS** | `OK` if the after-read matched the target; `FAILED` otherwise (UAC declined, registry locked, etc.) |
 | **Mechanism** | The exact registry path + value type, or the Win32 / DLL function called for non-registry settings |
 | **Before** | The raw bytes / number / string GamerGuardian read before the write, plus a parenthesized friendly description |
@@ -290,6 +290,20 @@ A silent auto-apply that fixed Game Mode after a Windows update reset it:
   Verify    : (Get-ItemProperty 'HKCU:\Software\Microsoft\GameBar' -Name AutoGameModeEnabled).AutoGameModeEnabled
 ```
 
+A pause / resume cycle while a fullscreen game runs:
+
+```
+[2026-05-06 19:42:01] [pause ] PAUSED  fullscreen (Cyberpunk2077)
+[2026-05-06 21:18:14] [pause ] RESUMED was: fullscreen (Cyberpunk2077)
+```
+
+A preference toggle in the Settings UI:
+
+```
+[2026-05-06 22:42:15] [ui    ] PREF   Fullscreen optimizations (global)  |  Monitor: False -> True
+[2026-05-06 22:42:16] [ui    ] PREF   Fullscreen optimizations (global)  |  AutoApply: False -> True
+```
+
 A failed Apply where the user cancelled the UAC prompt:
 
 ```

src/GamerGuardian/Native/Shell32.cs

@@ -66,6 +66,20 @@ public static bool IsFullscreenAppActive()
         return IsForegroundBorderlessFullscreen();
     }
 
+    public static string? GetForegroundProcessName()
+    {
+        try
+        {
+            var hwnd = GetForegroundWindow();
+            if (hwnd == IntPtr.Zero) return null;
+            GetWindowThreadProcessId(hwnd, out var pid);
+            if (pid == 0) return null;
+            using var p = System.Diagnostics.Process.GetProcessById((int)pid);
+            return p.ProcessName;
+        }
+        catch { return null; }
+    }
+
     private static bool IsForegroundBorderlessFullscreen()
     {
         try

src/GamerGuardian/Services/ChangeLogger.cs

@@ -54,6 +54,22 @@ public static void LogPreferenceChange(string settingName, string field, string
         catch { }
     }
 
+    /// <summary>
+    /// Records the start or end of a polling pause (fullscreen / benchmark / user).
+    /// </summary>
+    public static void LogPauseEvent(string action, string reason)
+    {
+        try
+        {
+            var dir = Path.GetDirectoryName(LogPath);
+            if (!string.IsNullOrEmpty(dir)) Directory.CreateDirectory(dir);
+            RotateIfNeeded();
+            var line = $"[{DateTime.Now:yyyy-MM-dd HH:mm:ss}] [pause ] {action,-7} {reason}";
+            File.AppendAllText(LogPath, line + Environment.NewLine, Encoding.UTF8);
+        }
+        catch { }
+    }
+
     private static string Format(ApplyResult r, string source)
     {
         var status = r.Verified ? "OK" : "FAILED";

src/GamerGuardian/Services/MonitorService.cs

@@ -14,6 +14,7 @@ public sealed class MonitorService : IDisposable
     private bool _running;
     private int _ticksSinceTrim;
     private bool _userPaused;
+    private string? _activePauseReason;
 
     public bool IsUserPaused => _userPaused;
     public event Action<bool>? PauseChanged;
@@ -63,9 +64,31 @@ private async Task TickAsync()
         }
         try
         {
-            if (_userPaused) return;
-            if (Shell32.IsFullscreenAppActive()) return;
-            if (BenchmarkDetector.GetRunningBenchmark() is not null) return;
+            string? pauseReason = null;
+            if (_userPaused)
+            {
+                pauseReason = "user (manual pause via tray)";
+            }
+            else if (Shell32.IsFullscreenAppActive())
+            {
+                var fg = Shell32.GetForegroundProcessName();
+                pauseReason = string.IsNullOrEmpty(fg) ? "fullscreen" : $"fullscreen ({fg})";
+            }
+            else if (BenchmarkDetector.GetRunningBenchmark() is { } bench)
+            {
+                pauseReason = $"benchmark ({bench})";
+            }
+
+            if (pauseReason != _activePauseReason)
+            {
+                if (pauseReason != null)
+                    ChangeLogger.LogPauseEvent("PAUSED", pauseReason);
+                else if (_activePauseReason != null)
+                    ChangeLogger.LogPauseEvent("RESUMED", $"was: {_activePauseReason}");
+                _activePauseReason = pauseReason;
+            }
+
+            if (pauseReason != null) return;
 
             var config = _store.Load();
             var drifted = new List<DriftItem>();