diff --git a/LibreHardwareMonitor.Windows.WinUI.Tests/Composition/ServiceCollectionExtensionsTests.cs b/LibreHardwareMonitor.Windows.WinUI.Tests/Composition/ServiceCollectionExtensionsTests.cs
new file mode 100644
index 0000000..42d4d8e
--- /dev/null
+++ b/LibreHardwareMonitor.Windows.WinUI.Tests/Composition/ServiceCollectionExtensionsTests.cs
@@ -0,0 +1,49 @@
+// 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.Linq;
+using LibreHardwareMonitor.Windows.WinUI.Composition;
+using LibreHardwareMonitor.Windows.WinUI.Services;
+using LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
+using LibreHardwareMonitor.Windows.WinUI.ViewModels;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace LibreHardwareMonitor.Windows.WinUI.Tests.Composition;
+
+// Guards the single composition root: every dependency referenced by a registered service must
+// itself be registered, otherwise the app fails to resolve its graph at launch. ValidateOnBuild
+// builds the dependency call sites without instantiating the services, so this stays off the real
+// hardware-monitor / kernel-driver path while still catching missing registrations.
+public class ServiceCollectionExtensionsTests
+{
+    [Fact]
+    public void AddAppServices_BuildsProviderWithoutMissingRegistrations()
+    {
+        ServiceProvider provider = new ServiceCollection()
+            .AddAppServices(NoOpStartupTracer.Instance)
+            .BuildServiceProvider(new ServiceProviderOptions { ValidateOnBuild = true });
+
+        Assert.NotNull(provider);
+        provider.Dispose();
+    }
+
+    [Theory]
+    [InlineData(typeof(AppSettings))]
+    [InlineData(typeof(IStartupTracer))]
+    [InlineData(typeof(IHardwareMonitorService))]
+    [InlineData(typeof(ILogger))]
+    [InlineData(typeof(IRemoteWebServer))]
+    [InlineData(typeof(SensorSelectionService))]
+    [InlineData(typeof(PlotTrackingService))]
+    [InlineData(typeof(StartupService))]
+    [InlineData(typeof(MainWindowViewModel))]
+    [InlineData(typeof(IMainWindowRuntimeFactory))]
+    public void AddAppServices_RegistersExpectedService(System.Type serviceType)
+    {
+        IServiceCollection services = new ServiceCollection().AddAppServices(NoOpStartupTracer.Instance);
+
+        Assert.Contains(services, descriptor => descriptor.ServiceType == serviceType);
+    }
+}
diff --git a/LibreHardwareMonitor.Windows.WinUI.Tests/ViewModels/MainWindowViewModelTests.cs b/LibreHardwareMonitor.Windows.WinUI.Tests/ViewModels/MainWindowViewModelTests.cs
new file mode 100644
index 0000000..7f5ea74
--- /dev/null
+++ b/LibreHardwareMonitor.Windows.WinUI.Tests/ViewModels/MainWindowViewModelTests.cs
@@ -0,0 +1,41 @@
+// 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 LibreHardwareMonitor.Windows.WinUI.Services;
+using LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
+using LibreHardwareMonitor.Windows.WinUI.ViewModels;
+using Moq;
+using Xunit;
+
+namespace LibreHardwareMonitor.Windows.WinUI.Tests.ViewModels;
+
+// Demonstrates the headline win of the DI refactor: MainWindowViewModel can now be constructed with
+// faked domain services (no real hardware monitor / kernel driver), and it reads its settings and
+// wires the web-server root provider during construction.
+public class MainWindowViewModelTests
+{
+    [Fact]
+    public void Constructor_WithFakedServices_ReadsSettingsAndWiresWebServerRoot()
+    {
+        AppSettings settings = AppSettings.LoadDefault();
+        var hardwareMonitor = new Mock<IHardwareMonitorService>();
+        var logger = new Mock<ILogger>();
+        var webServer = new Mock<IRemoteWebServer>();
+
+        using var viewModel = new MainWindowViewModel(
+            settings,
+            hardwareMonitor.Object,
+            logger.Object,
+            new SensorSelectionService(settings),
+            webServer.Object,
+            new PlotTrackingService(),
+            new StartupService(),
+            NoOpStartupTracer.Instance);
+
+        Assert.True(viewModel.ShowValueColumn);
+        Assert.True(viewModel.ShowMaxColumn);
+        webServer.Verify(s => s.SetRootProvider(It.IsAny<Func<SensorTreeItemViewModel?>>()), Times.Once);
+    }
+}
diff --git a/LibreHardwareMonitor.Windows.WinUI/Composition/ServiceCollectionExtensions.cs b/LibreHardwareMonitor.Windows.WinUI/Composition/ServiceCollectionExtensions.cs
index 14d9e0b..20a81c4 100644
--- a/LibreHardwareMonitor.Windows.WinUI/Composition/ServiceCollectionExtensions.cs
+++ b/LibreHardwareMonitor.Windows.WinUI/Composition/ServiceCollectionExtensions.cs
@@ -7,6 +7,7 @@ using LibreHardwareMonitor.Windows.WinUI.Services;
 using LibreHardwareMonitor.Windows.WinUI.Services.Tracing;
 using LibreHardwareMonitor.Windows.WinUI.ViewModels;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.UI.Dispatching;
 
 namespace LibreHardwareMonitor.Windows.WinUI.Composition;
 
@@ -54,7 +55,8 @@ internal static class ServiceCollectionExtensions
             sp.GetRequiredService<IRemoteWebServer>(),
             sp.GetRequiredService<PlotTrackingService>(),
             sp.GetRequiredService<StartupService>(),
-            sp.GetRequiredService<IStartupTracer>()));
+            sp.GetRequiredService<IStartupTracer>(),
+            DispatcherQueue.GetForCurrentThread()));
 
         // Runtime/window-tied service factory. The window itself is constructed by App (kept out of the
         // container so the XAML-tied Window is not a container-managed singleton).
diff --git a/LibreHardwareMonitor.Windows.WinUI/ViewModels/MainWindowViewModel.cs b/LibreHardwareMonitor.Windows.WinUI/ViewModels/MainWindowViewModel.cs
index a67bafa..3f6d081 100644
--- a/LibreHardwareMonitor.Windows.WinUI/ViewModels/MainWindowViewModel.cs
+++ b/LibreHardwareMonitor.Windows.WinUI/ViewModels/MainWindowViewModel.cs
@@ -83,7 +83,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
     ];
 
     private readonly IHardwareMonitorService _hardwareMonitor;
-    private readonly DispatcherQueue _dispatcherQueue;
+    private readonly DispatcherQueue? _dispatcherQueue;
     private readonly ILogger _logger;
     private readonly PlotTrackingService _plotTracking;
     private readonly SensorSelectionService _sensorSelection;
@@ -125,12 +125,13 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
         IRemoteWebServer remoteWebServer,
         PlotTrackingService plotTracking,
         StartupService startupService,
-        IStartupTracer startupTrace)
+        IStartupTracer startupTrace,
+        DispatcherQueue? dispatcherQueue = null)
     {
         Settings = settings;
         _startupTrace = startupTrace;
         _startupTrace.Mark("MainWindowViewModel.Constructor.Begin");
-        _dispatcherQueue = DispatcherQueue.GetForCurrentThread();
+        _dispatcherQueue = dispatcherQueue;
         _hardwareMonitor = hardwareMonitor;
         _logger = logger;
         _sensorSelection = sensorSelection;
@@ -941,7 +942,7 @@ public sealed class MainWindowViewModel : ViewModelBase, IDisposable
 
     private void HardwareMonitor_TreeRebuilt(object? sender, EventArgs e)
     {
-        if (_dispatcherQueue.HasThreadAccess)
+        if (_dispatcherQueue is null || _dispatcherQueue.HasThreadAccess)
         {
             UpdateRoot();
             UpdateStatus();