Extract startup tracing behind IStartupTracer abstraction

Add Microsoft.Extensions.DependencyInjection package and introduce an
IStartupTracer abstraction with NoOpStartupTracer (zero-overhead default)
and FileStartupTracer (renamed from WinUiStartupTrace). A StartupTracer
factory selects the implementation from environment configuration.

Consumers (App, MainWindow, MainWindowViewModel, SensorColumnMeasurer) now
depend on the non-nullable interface, removing null-conditional trace calls
and decoupling startup instrumentation from construction logic. No behavior
change: tracing still writes the same log when enabled.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

LibreHardwareMonitor.Windows.WinUI/App.xaml.cs

@@ -5,7 +5,7 @@
 using System;
 using System.IO;
 using System.Threading.Tasks;
-using LibreHardwareMonitor.Windows.WinUI.Services;
+using LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
 using Microsoft.UI.Xaml;
 using IOPath = System.IO.Path;
 
@@ -14,13 +14,13 @@ namespace LibreHardwareMonitor.Windows.WinUI;
 public partial class App : Application
 {
     private bool _launchStarted;
-    private readonly WinUiStartupTrace? _startupTrace;
+    private readonly IStartupTracer _startupTrace;
     private Window? _window;
 
     public App()
     {
-        _startupTrace = WinUiStartupTrace.Create();
-        _startupTrace?.Mark("App.Constructor.Begin");
+        _startupTrace = StartupTracer.Create();
+        _startupTrace.Mark("App.Constructor.Begin");
         MeasureStartup("App.WireExceptionHandlers", () =>
         {
             UnhandledException += App_UnhandledException;
@@ -28,8 +28,8 @@ public partial class App : Application
             TaskScheduler.UnobservedTaskException += TaskScheduler_UnobservedTaskException;
         });
         MeasureStartup("App.InitializeComponent", InitializeComponent);
-        _startupTrace?.Mark("App.Constructor.Complete");
-        _startupTrace?.Flush();
+        _startupTrace.Mark("App.Constructor.Complete");
+        _startupTrace.Flush();
     }
 
     protected override void OnLaunched(LaunchActivatedEventArgs args)
@@ -45,18 +45,18 @@ public partial class App : Application
         _launchStarted = true;
         try
         {
-            _startupTrace?.Mark("App.LaunchMainWindow.Begin");
+            _startupTrace.Mark("App.LaunchMainWindow.Begin");
             MainWindow mainWindow = MeasureStartup("App.CreateMainWindow", () => new MainWindow(_startupTrace));
             _window = mainWindow;
             MeasureStartup("App.ActivateWindow", mainWindow.Activate);
             MeasureStartup("App.StartMonitoringAfterActivation", mainWindow.StartMonitoringAfterActivation);
-            _startupTrace?.Mark("App.LaunchMainWindow.Complete");
-            _startupTrace?.Flush();
+            _startupTrace.Mark("App.LaunchMainWindow.Complete");
+            _startupTrace.Flush();
         }
         catch (Exception ex)
         {
-            _startupTrace?.Mark("App.LaunchMainWindow.Exception", $"{ex.GetType().FullName}: {ex.Message}");
-            _startupTrace?.Flush();
+            _startupTrace.Mark("App.LaunchMainWindow.Exception", $"{ex.GetType().FullName}: {ex.Message}");
+            _startupTrace.Flush();
             WriteExceptionLog("Window launch failed", ex);
             throw;
         }
@@ -64,20 +64,11 @@ public partial class App : Application
 
     private void MeasureStartup(string phase, Action action)
     {
-        if (_startupTrace == null)
-        {
-            action();
-            return;
-        }
-
         _startupTrace.Measure(phase, action);
     }
 
     private T MeasureStartup<T>(string phase, Func<T> action)
     {
-        if (_startupTrace == null)
-            return action();
-
         return _startupTrace.Measure(phase, action);
     }
 

LibreHardwareMonitor.Windows.WinUI/LibreHardwareMonitor.Windows.WinUI.csproj

@@ -21,6 +21,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="10.0.8" />
     <PackageReference Include="Microsoft.WindowsAppSDK" Version="2.0.1" />
   </ItemGroup>
 

LibreHardwareMonitor.Windows.WinUI/MainWindow.cs

@@ -12,6 +12,7 @@ using System.Threading.Tasks;
 using LibreHardwareMonitor.Hardware;
 using LibreHardwareMonitor.Windows.WinUI.Controls;
 using LibreHardwareMonitor.Windows.WinUI.Services;
+using LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
 using LibreHardwareMonitor.Windows.WinUI.Utilities;
 using LibreHardwareMonitor.Windows.WinUI.ViewModels;
 using Microsoft.UI;
@@ -33,7 +34,7 @@ public sealed partial class MainWindow : Window
     private readonly WindowChromeManager _chromeManager;
     private readonly WindowPlacementService _placementService;
     private readonly DispatcherQueueTimer _timer;
-    private readonly WinUiStartupTrace? _startupTrace;
+    private readonly IStartupTracer _startupTrace;
     private readonly TrayIconService _trayIconService;
     private readonly DialogService _dialogService;
     private readonly SensorColumnMeasurer _columnMeasurer;
@@ -50,14 +51,14 @@ public sealed partial class MainWindow : Window
     private bool _sensorTreeRebuildQueued;
     private bool _sensorColumnWidthUpdateQueued;
 
-    public MainWindow() : this(null)
+    public MainWindow() : this(NoOpStartupTracer.Instance)
     {
     }
 
-    internal MainWindow(WinUiStartupTrace? startupTrace)
+    internal MainWindow(IStartupTracer startupTrace)
     {
         _startupTrace = startupTrace;
-        _startupTrace?.Mark("MainWindow.Constructor.Begin");
+        _startupTrace.Mark("MainWindow.Constructor.Begin");
         AppSettings settings = MeasureStartup("MainWindow.LoadSettings", AppSettings.LoadDefault);
         ViewModel = MeasureStartup("MainWindow.CreateViewModel", () => new MainWindowViewModel(settings, _startupTrace));
 
@@ -159,14 +160,14 @@ public sealed partial class MainWindow : Window
 
             Closed += MainWindow_Closed;
         });
-        _startupTrace?.Mark("MainWindow.Constructor.Complete");
+        _startupTrace.Mark("MainWindow.Constructor.Complete");
     }
 
     public MainWindowViewModel ViewModel { get; }
 
     public void StartMonitoringAfterActivation()
     {
-        _startupTrace?.Mark("MainWindow.StartMonitoringAfterActivation.Queued");
+        _startupTrace.Mark("MainWindow.StartMonitoringAfterActivation.Queued");
         if (!DispatcherQueue.TryEnqueue(async () =>
         {
             if (_isMonitoringStarted)
@@ -175,27 +176,27 @@ public sealed partial class MainWindow : Window
             _isMonitoringStarted = true;
             try
             {
-                _startupTrace?.Mark("MainWindow.StartMonitoringAfterActivation.Begin");
+                _startupTrace.Mark("MainWindow.StartMonitoringAfterActivation.Begin");
                 ApplyInitialWindowState();
                 await MeasureStartupAsync("MainWindowViewModel.StartAsync", ViewModel.StartAsync);
                 SyncTraySensors();
                 SyncGadgetSensors();
                 UpdateGadgetVisibility();
                 MeasureStartup("MainWindow.StartTimer", _timer.Start);
-                _startupTrace?.Mark("MainWindow.StartMonitoringAfterActivation.Complete");
+                _startupTrace.Mark("MainWindow.StartMonitoringAfterActivation.Complete");
                 RequestStartupTraceComplete();
-                _startupTrace?.Flush();
+                _startupTrace.Flush();
             }
             catch (Exception ex)
             {
-                _startupTrace?.Mark("MainWindow.StartMonitoringAfterActivation.Exception", $"{ex.GetType().FullName}: {ex.Message}");
-                _startupTrace?.Flush();
+                _startupTrace.Mark("MainWindow.StartMonitoringAfterActivation.Exception", $"{ex.GetType().FullName}: {ex.Message}");
+                _startupTrace.Flush();
                 RecordRuntimeError("Hardware initialization failed", ex);
             }
         }))
         {
-            _startupTrace?.Mark("MainWindow.StartMonitoringAfterActivation.EnqueueFailed");
-            _startupTrace?.Flush();
+            _startupTrace.Mark("MainWindow.StartMonitoringAfterActivation.EnqueueFailed");
+            _startupTrace.Flush();
         }
     }
 
@@ -207,8 +208,8 @@ public sealed partial class MainWindow : Window
     private void RootGrid_Loaded(object sender, RoutedEventArgs e)
     {
         RootGrid.Loaded -= RootGrid_Loaded;
-        _startupTrace?.Mark("MainWindow.RootLoaded", GetRootSizeDetail());
-        _startupTrace?.Flush();
+        _startupTrace.Mark("MainWindow.RootLoaded", GetRootSizeDetail());
+        _startupTrace.Flush();
     }
 
     private void RootGrid_LayoutUpdated(object? sender, object e)
@@ -218,13 +219,13 @@ public sealed partial class MainWindow : Window
 
         _firstLayoutRecorded = true;
         RootGrid.LayoutUpdated -= RootGrid_LayoutUpdated;
-        _startupTrace?.Mark("MainWindow.FirstLayoutUpdated", GetRootSizeDetail());
-        _startupTrace?.Flush();
+        _startupTrace.Mark("MainWindow.FirstLayoutUpdated", GetRootSizeDetail());
+        _startupTrace.Flush();
     }
 
     private void MeasureStartup(string phase, Action action)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
         {
             action();
             return;
@@ -235,7 +236,7 @@ public sealed partial class MainWindow : Window
 
     private void MeasureStartup(string phase, Action action, Func<string> getDetail)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
         {
             action();
             return;
@@ -246,7 +247,7 @@ public sealed partial class MainWindow : Window
 
     private T MeasureStartup<T>(string phase, Func<T> action)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
             return action();
 
         return _startupTrace.Measure(phase, action);
@@ -254,7 +255,7 @@ public sealed partial class MainWindow : Window
 
     private async Task MeasureStartupAsync(string phase, Func<Task> action)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
         {
             await action();
             return;
@@ -427,8 +428,8 @@ public sealed partial class MainWindow : Window
 
     private void RecordRuntimeError(string message, Exception exception)
     {
-        _startupTrace?.Mark("MainWindow.RuntimeError", $"{message}: {exception.GetType().FullName}: {exception.Message}");
-        _startupTrace?.Flush();
+        _startupTrace.Mark("MainWindow.RuntimeError", $"{message}: {exception.GetType().FullName}: {exception.Message}");
+        _startupTrace.Flush();
 
         // Use a dedicated runtime log (not the startup log that App.xaml.cs appends to) and write it only once, so a
         // recurring per-tick failure neither clobbers the startup diagnostics nor grows the file without bound.
@@ -466,7 +467,7 @@ public sealed partial class MainWindow : Window
         _secondaryWindows.CloseAll();
         _placementService.Save();
         ViewModel.Dispose();
-        _startupTrace?.Dispose();
+        _startupTrace.Dispose();
     }
 
     private void AppWindow_Changed(AppWindow sender, AppWindowChangedEventArgs args)
@@ -566,7 +567,7 @@ public sealed partial class MainWindow : Window
 
     private void CompleteStartupTraceIfReady()
     {
-        if (_startupCompleteRecorded || _startupTrace is not { IsComplete: false } || _columnMeasurer.RowCount == 0)
+        if (_startupCompleteRecorded || _startupTrace.IsComplete || _columnMeasurer.RowCount == 0)
             return;
 
         _startupCompleteRecorded = true;

LibreHardwareMonitor.Windows.WinUI/Services/SensorColumnMeasurer.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Generic;
+using LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
 using LibreHardwareMonitor.Windows.WinUI.ViewModels;
 using Microsoft.UI.Dispatching;
 using Microsoft.UI.Xaml;
@@ -24,7 +25,7 @@ internal sealed class SensorColumnMeasurer
     private static readonly TimeSpan SettleDelay = TimeSpan.FromSeconds(5);
 
     private readonly MainWindowViewModel _viewModel;
-    private readonly WinUiStartupTrace? _startupTrace;
+    private readonly IStartupTracer _startupTrace;
     private readonly Dictionary<(string Text, bool Bold), double> _cache = new();
     private readonly List<Grid> _rowGrids = [];
     private readonly DispatcherQueueTimer _settleTimer;
@@ -34,7 +35,7 @@ internal sealed class SensorColumnMeasurer
     private double _stableDeviceColumnWidth = DefaultDeviceColumnWidth;
     private bool _settled;
 
-    public SensorColumnMeasurer(DispatcherQueue dispatcherQueue, MainWindowViewModel viewModel, WinUiStartupTrace? startupTrace)
+    public SensorColumnMeasurer(DispatcherQueue dispatcherQueue, MainWindowViewModel viewModel, IStartupTracer startupTrace)
     {
         _viewModel = viewModel ?? throw new ArgumentNullException(nameof(viewModel));
         _startupTrace = startupTrace;
@@ -215,6 +216,6 @@ internal sealed class SensorColumnMeasurer
             return;
 
         _viewModel.Settings.SetValue(DeviceColumnWidthSetting, measuredWidth);
-        _startupTrace?.Mark("MainWindow.RecordDeviceColumnWidth", FormattableString.Invariant($"width={measuredWidth:F0}, rows={_rowGrids.Count}"));
+        _startupTrace.Mark("MainWindow.RecordDeviceColumnWidth", FormattableString.Invariant($"width={measuredWidth:F0}, rows={_rowGrids.Count}"));
     }
 }

LibreHardwareMonitor.Windows.WinUI/Services/Tracing/FileStartupTracer.cs

@@ -11,13 +11,14 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
-namespace LibreHardwareMonitor.Windows.WinUI.Services;
+namespace LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
 
-internal sealed class WinUiStartupTrace : IDisposable
+/// <summary>
+/// File-writing startup tracer. Records phase timings and flushes them to a CSV-style log.
+/// Created via <see cref="StartupTracer.Create"/> when startup timing is enabled.
+/// </summary>
+internal sealed class FileStartupTracer : IStartupTracer
 {
-    private const string EnabledEnvironmentVariable = "LHM_WINUI_STARTUP_TIMING";
-    private const string PathEnvironmentVariable = "LHM_WINUI_STARTUP_TIMING_PATH";
-
     private readonly List<Entry> _entries = new();
     private readonly string _fileName;
     private readonly object _lock = new();
@@ -25,9 +26,9 @@ internal sealed class WinUiStartupTrace : IDisposable
     private bool _completed;
     private bool _disposed;
 
-    private WinUiStartupTrace()
+    internal FileStartupTracer(string fileName)
     {
-        _fileName = GetLogFileName();
+        _fileName = fileName;
         _totalStopwatch = Stopwatch.StartNew();
         Mark("WinUIStartupTrace.Begin");
     }
@@ -41,11 +42,6 @@ internal sealed class WinUiStartupTrace : IDisposable
         }
     }
 
-    public static WinUiStartupTrace? Create()
-    {
-        return IsEnabled() ? new WinUiStartupTrace() : null;
-    }
-
     public void Complete(string phase, string detail = "")
     {
         bool shouldWrite;
@@ -231,38 +227,6 @@ internal sealed class WinUiStartupTrace : IDisposable
         }
     }
 
-    private static string GetLogFileName()
-    {
-        string? configuredPath = Environment.GetEnvironmentVariable(PathEnvironmentVariable);
-
-        string fileName = $"LibreHardwareMonitor.WinUIStartupTiming-{DateTime.Now:yyyyMMdd-HHmmss-fff}.log";
-        if (string.IsNullOrWhiteSpace(configuredPath))
-            return Path.Combine(AppContext.BaseDirectory, fileName);
-
-        if (configuredPath.EndsWith(Path.DirectorySeparatorChar.ToString(), StringComparison.Ordinal)
-            || configuredPath.EndsWith(Path.AltDirectorySeparatorChar.ToString(), StringComparison.Ordinal)
-            || Directory.Exists(configuredPath))
-        {
-            return Path.Combine(configuredPath, fileName);
-        }
-
-        return configuredPath;
-    }
-
-    private static bool IsEnabled()
-    {
-        string environmentValue = Environment.GetEnvironmentVariable(EnabledEnvironmentVariable) ?? "";
-        return IsTruthy(environmentValue);
-    }
-
-    private static bool IsTruthy(string value)
-    {
-        return value.Equals("1", StringComparison.OrdinalIgnoreCase)
-               || value.Equals("true", StringComparison.OrdinalIgnoreCase)
-               || value.Equals("yes", StringComparison.OrdinalIgnoreCase)
-               || value.Equals("on", StringComparison.OrdinalIgnoreCase);
-    }
-
     private void AddEntry(string phase, TimeSpan elapsed, string status, string detail)
     {
         AddEntry(phase, _totalStopwatch.Elapsed, elapsed, status, detail);

LibreHardwareMonitor.Windows.WinUI/Services/Tracing/IStartupTracer.cs

@@ -0,0 +1,39 @@
+// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// Copyright (C) LibreHardwareMonitor and Contributors.
+
+using System;
+using System.Threading.Tasks;
+
+namespace LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
+
+/// <summary>
+/// Optional startup instrumentation consumed by startup operations. A no-op implementation
+/// is used when tracing is disabled, so callers never need null checks.
+/// </summary>
+internal interface IStartupTracer : IDisposable
+{
+    bool IsComplete { get; }
+
+    void Mark(string phase, string detail = "");
+
+    void Complete(string phase, string detail = "");
+
+    void Flush();
+
+    void Measure(string phase, Action action);
+
+    void Measure(string phase, Action action, Func<string>? getDetail);
+
+    T Measure<T>(string phase, Func<T> action);
+
+    T Measure<T>(string phase, Func<T> action, Func<T, string>? getDetail);
+
+    Task MeasureAsync(string phase, Func<Task> action);
+
+    Task MeasureAsync(string phase, Func<Task> action, Func<string>? getDetail);
+
+    Task<T> MeasureAsync<T>(string phase, Func<Task<T>> action);
+
+    Task<T> MeasureAsync<T>(string phase, Func<Task<T>> action, Func<T, string>? getDetail);
+}

LibreHardwareMonitor.Windows.WinUI/Services/Tracing/NoOpStartupTracer.cs

@@ -0,0 +1,79 @@
+// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// Copyright (C) LibreHardwareMonitor and Contributors.
+
+using System;
+using System.Threading.Tasks;
+
+namespace LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
+
+/// <summary>
+/// Zero-overhead tracer used when startup tracing is disabled. Measure overloads simply
+/// invoke the supplied delegate; everything else is a no-op.
+/// </summary>
+internal sealed class NoOpStartupTracer : IStartupTracer
+{
+    public static readonly NoOpStartupTracer Instance = new();
+
+    private NoOpStartupTracer()
+    {
+    }
+
+    public bool IsComplete => false;
+
+    public void Mark(string phase, string detail = "")
+    {
+    }
+
+    public void Complete(string phase, string detail = "")
+    {
+    }
+
+    public void Flush()
+    {
+    }
+
+    public void Measure(string phase, Action action)
+    {
+        action();
+    }
+
+    public void Measure(string phase, Action action, Func<string>? getDetail)
+    {
+        action();
+    }
+
+    public T Measure<T>(string phase, Func<T> action)
+    {
+        return action();
+    }
+
+    public T Measure<T>(string phase, Func<T> action, Func<T, string>? getDetail)
+    {
+        return action();
+    }
+
+    public Task MeasureAsync(string phase, Func<Task> action)
+    {
+        return action();
+    }
+
+    public Task MeasureAsync(string phase, Func<Task> action, Func<string>? getDetail)
+    {
+        return action();
+    }
+
+    public Task<T> MeasureAsync<T>(string phase, Func<Task<T>> action)
+    {
+        return action();
+    }
+
+    public Task<T> MeasureAsync<T>(string phase, Func<Task<T>> action, Func<T, string>? getDetail)
+    {
+        return action();
+    }
+
+    public void Dispose()
+    {
+    }
+}

LibreHardwareMonitor.Windows.WinUI/Services/Tracing/StartupTracer.cs

@@ -0,0 +1,56 @@
+// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// Copyright (C) LibreHardwareMonitor and Contributors.
+
+using System;
+using System.IO;
+
+namespace LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
+
+/// <summary>
+/// Factory that selects the appropriate <see cref="IStartupTracer"/> based on environment
+/// configuration. Returns a <see cref="FileStartupTracer"/> when timing is enabled, otherwise
+/// the shared <see cref="NoOpStartupTracer"/>.
+/// </summary>
+internal static class StartupTracer
+{
+    private const string EnabledEnvironmentVariable = "LHM_WINUI_STARTUP_TIMING";
+    private const string PathEnvironmentVariable = "LHM_WINUI_STARTUP_TIMING_PATH";
+
+    public static IStartupTracer Create()
+    {
+        return IsEnabled() ? new FileStartupTracer(GetLogFileName()) : NoOpStartupTracer.Instance;
+    }
+
+    private static string GetLogFileName()
+    {
+        string? configuredPath = Environment.GetEnvironmentVariable(PathEnvironmentVariable);
+
+        string fileName = $"LibreHardwareMonitor.WinUIStartupTiming-{DateTime.Now:yyyyMMdd-HHmmss-fff}.log";
+        if (string.IsNullOrWhiteSpace(configuredPath))
+            return Path.Combine(AppContext.BaseDirectory, fileName);
+
+        if (configuredPath.EndsWith(Path.DirectorySeparatorChar.ToString(), StringComparison.Ordinal)
+            || configuredPath.EndsWith(Path.AltDirectorySeparatorChar.ToString(), StringComparison.Ordinal)
+            || Directory.Exists(configuredPath))
+        {
+            return Path.Combine(configuredPath, fileName);
+        }
+
+        return configuredPath;
+    }
+
+    private static bool IsEnabled()
+    {
+        string environmentValue = Environment.GetEnvironmentVariable(EnabledEnvironmentVariable) ?? "";
+        return IsTruthy(environmentValue);
+    }
+
+    private static bool IsTruthy(string value)
+    {
+        return value.Equals("1", StringComparison.OrdinalIgnoreCase)
+               || value.Equals("true", StringComparison.OrdinalIgnoreCase)
+               || value.Equals("yes", StringComparison.OrdinalIgnoreCase)
+               || value.Equals("on", StringComparison.OrdinalIgnoreCase);
+    }
+}

LibreHardwareMonitor.Windows.WinUI/ViewModels/MainWindowViewModel.cs

@@ -11,6 +11,7 @@ using System.Threading.Tasks;
 using LibreHardwareMonitor.Hardware;
 using LibreHardwareMonitor.Hardware.Storage;
 using LibreHardwareMonitor.Windows.WinUI.Services;
+using LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
 using LibreHardwareMonitor.Windows.WinUI.Utilities;
 using Microsoft.UI.Dispatching;
 using Microsoft.UI.Xaml;
@@ -88,7 +89,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
     private readonly SensorSelectionService _sensorSelection;
     private readonly RemoteWebServer _remoteWebServer;
     private readonly StartupService _startupService = new();
-    private readonly WinUiStartupTrace? _startupTrace;
+    private readonly IStartupTracer _startupTrace;
     private AppThemeMode _themeMode;
     private int _loggingIntervalIndex;
     private PlotLocation _plotLocation;
@@ -115,15 +116,15 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
     private TemperatureUnit _temperatureUnit;
     private int _updateIntervalIndex;
 
-    public MainWindowViewModel(AppSettings settings) : this(settings, null)
+    public MainWindowViewModel(AppSettings settings) : this(settings, NoOpStartupTracer.Instance)
     {
     }
 
-    internal MainWindowViewModel(AppSettings settings, WinUiStartupTrace? startupTrace)
+    internal MainWindowViewModel(AppSettings settings, IStartupTracer startupTrace)
     {
         Settings = settings;
         _startupTrace = startupTrace;
-        _startupTrace?.Mark("MainWindowViewModel.Constructor.Begin");
+        _startupTrace.Mark("MainWindowViewModel.Constructor.Begin");
         _dispatcherQueue = DispatcherQueue.GetForCurrentThread();
         _hardwareMonitor = new HardwareMonitorService(settings);
         _logger = new Logger(_hardwareMonitor.Computer);
@@ -162,7 +163,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
         StorageDevice.ThrottleInterval = _throttleAtaUpdate ? TimeSpan.FromSeconds(30) : TimeSpan.Zero;
         _logger.LoggingInterval = LoggingIntervals[_loggingIntervalIndex];
         _logger.FileRotationMethod = (LoggerFileRotation)Math.Clamp(settings.GetValue("logger.fileRotation", 0), 0, 1);
-        _startupTrace?.Mark("MainWindowViewModel.Constructor.Complete");
+        _startupTrace.Mark("MainWindowViewModel.Constructor.Complete");
     }
 
     public event EventHandler? PlotInvalidated;
@@ -864,7 +865,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
         try
         {
             IsHardwareLoading = true;
-            _startupTrace?.Mark("MainWindowViewModel.StartAsync.Begin");
+            _startupTrace.Mark("MainWindowViewModel.StartAsync.Begin");
             StatusText = "Initializing hardware sensors...";
             await MeasureStartupAsync("MainWindowViewModel.HardwareMonitor.OpenAsync", () => _hardwareMonitor.OpenAsync(raiseTreeRebuilt: false));
             MeasureStartup("MainWindowViewModel.UpdateRoot", UpdateRoot, GetRootDetail);
@@ -873,12 +874,12 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
             MeasureStartup("MainWindowViewModel.StartWebServerFromSettings", StartWebServerFromSettings);
             MeasureStartup("MainWindowViewModel.UpdateStatus", UpdateStatus, GetRootDetail);
             _isStarted = true;
-            _startupTrace?.Mark("MainWindowViewModel.StartAsync.Complete", GetRootDetail());
+            _startupTrace.Mark("MainWindowViewModel.StartAsync.Complete", GetRootDetail());
         }
         finally
         {
             IsHardwareLoading = false;
-            _startupTrace?.Mark("MainWindowViewModel.HardwareLoadingComplete", GetRootDetail());
+            _startupTrace.Mark("MainWindowViewModel.HardwareLoadingComplete", GetRootDetail());
             _isStarting = false;
         }
     }
@@ -951,7 +952,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
 
     private void MeasureStartup(string phase, Action action)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
         {
             action();
             return;
@@ -962,7 +963,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
 
     private void MeasureStartup(string phase, Action action, Func<string> getDetail)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
         {
             action();
             return;
@@ -973,7 +974,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
 
     private T MeasureStartup<T>(string phase, Func<T> action)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
             return action();
 
         return _startupTrace.Measure(phase, action);
@@ -981,7 +982,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
 
     private async Task MeasureStartupAsync(string phase, Func<Task> action)
     {
-        if (_startupTrace is not { IsComplete: false })
+        if (_startupTrace.IsComplete)
         {
             await action();
             return;