Extract a per-user background host so indexing can later run outside the window.

Keep the GUI as the index writer for now; mutex, named pipe, and opt-in logon autostart prepare Explorer.Host.exe without two SQLite writers.

Co-authored-by: Cursor <cursoragent@cursor.com>

Explorer.slnx

@@ -6,6 +6,8 @@
     <Project Path="src/Explorer.Contracts/Explorer.Contracts.csproj" />
     <Project Path="src/Explorer.Domain/Explorer.Domain.csproj" />
     <Project Path="src/Explorer.FileOperations/Explorer.FileOperations.csproj" />
+    <Project Path="src/Explorer.Host/Explorer.Host.csproj" />
+    <Project Path="src/Explorer.Hosting/Explorer.Hosting.csproj" />
     <Project Path="src/Explorer.Indexing/Explorer.Indexing.csproj" />
     <Project Path="src/Explorer.Plugin.Abstractions/Explorer.Plugin.Abstractions.csproj" />
     <Project Path="src/Explorer.Plugin.GoogleDrive/Explorer.Plugin.GoogleDrive.csproj" />
@@ -21,6 +23,7 @@
     <Project Path="tests/Explorer.Application.Tests/Explorer.Application.Tests.csproj" />
     <Project Path="tests/Explorer.Domain.Tests/Explorer.Domain.Tests.csproj" />
     <Project Path="tests/Explorer.FileOperations.Tests/Explorer.FileOperations.Tests.csproj" />
+    <Project Path="tests/Explorer.Hosting.Tests/Explorer.Hosting.Tests.csproj" />
     <Project Path="tests/Explorer.Indexing.Tests/Explorer.Indexing.Tests.csproj" />
     <Project Path="tests/Explorer.Search.Tests/Explorer.Search.Tests.csproj" />
     <Project Path="tests/Explorer.Storage.Tests/Explorer.Storage.Tests.csproj" />

src/Explorer.App/AppServices.cs

@@ -1,21 +1,11 @@
-using Explorer.Analysis;
 using Explorer.Application;
-using Explorer.Domain;
 using Explorer.Domain.Abstractions;
-using Explorer.FileOperations;
+using Explorer.Hosting;
-using Explorer.Indexing;
-using Explorer.Plugin.Abstractions;
-using Explorer.Plugin.GoogleDrive;
-using Explorer.Plugin.Nextcloud;
-using Explorer.Plugin.OneDrive;
 using Explorer.Presentation;
 using Explorer.Presentation.ViewModels;
-using Explorer.Search;
-using Explorer.Storage.Sqlite;
 using Explorer.Windows;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
-using Microsoft.Extensions.Logging;
 
 namespace Explorer.App;
 
@@ -23,105 +13,20 @@ public static class AppServices
 {
     public static IServiceCollection AddExplorer(this IServiceCollection services)
     {
-        services.AddSingleton<IClock, SystemClock>();
+        services.AddExplorerCore();
-        services.AddSingleton<IAppEnvironment, WindowsAppEnvironment>();
+        services.AddExplorerUi();
-        services.AddSingleton<IVolumeService, WindowsVolumeService>();
+        return services;
-        services.AddSingleton<IFileSystemEnumerator, WindowsFileSystemEnumerator>();
+    }
-        services.AddSingleton<IUsnJournal, WindowsUsnJournal>();
+
-        services.AddSingleton<IShellFileOperations, WindowsShellFileOperations>();
+    public static IServiceCollection AddExplorerUi(this IServiceCollection services)
-        services.AddSingleton<IOsClipboard, Services.WpfClipboard>();
-        services.AddSingleton<IIndexStore>(sp =>
     {
-            var env = sp.GetRequiredService<IAppEnvironment>();
+        services.AddSingleton<IOsClipboard, Services.WpfClipboard>();
-            var logger = sp.GetRequiredService<ILogger<SqliteIndexStore>>();
-            return new SqliteIndexStore(env.DatabasePath, logger);
-        });
-        services.AddSingleton<IStorageProvider, OneDriveStorageProvider>();
-        services.AddSingleton<IStorageProvider, GoogleDriveStorageProvider>();
-        services.AddSingleton<IStorageProvider, NextcloudStorageProvider>();
-        services.AddSingleton<StorageProviderRegistry>();
-        services.AddSingleton<IHydrationGuard, HydrationGuard>();
-        services.AddSingleton<IArchiveExecutor, SevenZipArchiveExecutor>();
-        services.AddSingleton<WindowsGitStatusProvider>();
-        services.AddSingleton<IGitStatusProvider>(sp => sp.GetRequiredService<WindowsGitStatusProvider>());
-        services.AddSingleton<IGitCommandProvider>(sp => sp.GetRequiredService<WindowsGitStatusProvider>());
         services.AddSingleton<IWorkspaceLauncher, WindowsWorkspaceLauncher>();
-        services.AddSingleton<IElevatedScanService, WindowsElevatedScanService>();
-        services.AddSingleton<IRecycleBinCatalog, WindowsRecycleBinCatalog>();
-        services.AddSingleton<SourceManager>();
-        services.AddSingleton<PathHistoryStore>();
-        services.AddSingleton<CloudPlaceStore>();
-        services.AddSingleton<UiPreferencesStore>();
-        services.AddSingleton<IArchiveCatalog, ArchiveCatalog>();
-        services.AddSingleton<ArchiveContentsIndexer>();
-        services.AddSingleton<BrowseService>();
         services.AddSingleton<ThumbnailService>();
         services.AddSingleton<IThumbnailService>(sp => sp.GetRequiredService<ThumbnailService>());
-        services.AddSingleton<FilesystemScanner>();
-        services.AddSingleton<FolderReconciler>();
-        services.AddSingleton<UsnChangeApplier>();
-        services.AddSingleton<IndexingCoordinator>();
-        services.AddSingleton<DirectoryWatcherHub>();
-        services.AddSingleton<SearchService>();
-        services.AddSingleton<AnalysisService>();
-        services.AddSingleton<IOperationExecutor, NativeFileOperationExecutor>();
-        services.AddSingleton<TransferQueue>();
-        services.AddSingleton<FileOperationService>();
-        services.AddSingleton<RenamePlanner>();
-        services.AddSingleton<RenameBatchService>();
-        services.AddSingleton<FolderSyncPlanner>();
-        services.AddSingleton<FolderSyncService>();
-        services.AddSingleton<FileOperationProfilePlanner>();
-        services.AddSingleton<OperationProfileService>();
-        services.AddSingleton<ReorganizePlanner>();
-        services.AddSingleton<ReorganizeService>();
-        services.AddSingleton<DuplicateHashWorker>();
-        services.AddSingleton<HistoryRollupService>();
         services.AddSingleton<MainViewModel>();
         services.AddSingleton<MainWindow>();
-        services.AddHostedService(sp => sp.GetRequiredService<IndexingCoordinator>());
-        services.AddHostedService(sp => sp.GetRequiredService<TransferQueue>());
-        services.AddHostedService(sp => sp.GetRequiredService<DuplicateHashWorker>());
-        services.AddHostedService(sp => sp.GetRequiredService<HistoryRollupService>());
         services.AddHostedService(sp => sp.GetRequiredService<ThumbnailService>());
-        services.AddHostedService<WatcherHostedService>();
         return services;
     }
 }
-
-public sealed class WatcherHostedService : BackgroundService
-{
-    private readonly DirectoryWatcherHub _hub;
-    private readonly SourceManager _sources;
-    private readonly TransferQueue _transfers;
-    private readonly FolderSyncService _sync;
-    private readonly OperationProfileService _profiles;
-
-    public WatcherHostedService(
-        DirectoryWatcherHub hub,
-        SourceManager sources,
-        TransferQueue transfers,
-        FolderSyncService sync,
-        OperationProfileService profiles)
-    {
-        _hub = hub;
-        _sources = sources;
-        _transfers = transfers;
-        _sync = sync;
-        _profiles = profiles;
-    }
-
-    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
-    {
-        using var timer = new PeriodicTimer(TimeSpan.FromSeconds(20));
-        await _hub.RefreshAsync(stoppingToken).ConfigureAwait(false);
-        while (await timer.WaitForNextTickAsync(stoppingToken).ConfigureAwait(false))
-        {
-            await _sources.RefreshOnlineStateAsync(forceRefresh: true, stoppingToken).ConfigureAwait(false);
-            _transfers.NotifyAvailability();
-            await _sync.TryAutoRunAsync(stoppingToken).ConfigureAwait(false);
-            await _profiles.TryAutoRunAsync(stoppingToken).ConfigureAwait(false);
-            await _hub.RefreshAsync(stoppingToken).ConfigureAwait(false);
-        }
-    }
-}

src/Explorer.App/Explorer.App.csproj

@@ -29,6 +29,10 @@
     <ProjectReference Include="..\Explorer.Application\Explorer.Application.csproj" />
     <ProjectReference Include="..\Explorer.Domain\Explorer.Domain.csproj" />
     <ProjectReference Include="..\Explorer.FileOperations\Explorer.FileOperations.csproj" />
+    <ProjectReference Include="..\Explorer.Host\Explorer.Host.csproj">
+      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+    </ProjectReference>
+    <ProjectReference Include="..\Explorer.Hosting\Explorer.Hosting.csproj" />
     <ProjectReference Include="..\Explorer.Indexing\Explorer.Indexing.csproj" />
     <ProjectReference Include="..\Explorer.Plugin.Abstractions\Explorer.Plugin.Abstractions.csproj" />
     <ProjectReference Include="..\Explorer.Plugin.GoogleDrive\Explorer.Plugin.GoogleDrive.csproj" />
@@ -39,4 +43,17 @@
     <ProjectReference Include="..\Explorer.Storage.Sqlite\Explorer.Storage.Sqlite.csproj" />
     <ProjectReference Include="..\Explorer.Windows\Explorer.Windows.csproj" />
   </ItemGroup>
+  <Target Name="CopyExplorerHost" AfterTargets="Build">
+    <PropertyGroup>
+      <_HostDir>$([System.IO.Path]::GetFullPath('$(MSBuildThisFileDirectory)..\Explorer.Host\bin\$(Configuration)\net10.0-windows\'))</_HostDir>
+    </PropertyGroup>
+    <ItemGroup>
+      <_HostFiles Include="$(_HostDir)Explorer.Host.exe" />
+      <_HostFiles Include="$(_HostDir)Explorer.Host.dll" />
+      <_HostFiles Include="$(_HostDir)Explorer.Host.deps.json" />
+      <_HostFiles Include="$(_HostDir)Explorer.Host.runtimeconfig.json" />
+      <_HostFiles Include="$(_HostDir)Explorer.Host.pdb" />
+    </ItemGroup>
+    <Copy SourceFiles="@(_HostFiles)" DestinationFolder="$(OutputPath)" SkipUnchangedFiles="true" Condition="Exists('$(_HostDir)Explorer.Host.exe')" />
+  </Target>
 </Project>

src/Explorer.App/SettingsWindow.xaml

@@ -61,6 +61,16 @@
                   Content="Include archive contents in the index"/>
         <TextBlock TextWrapping="Wrap" Foreground="{DynamicResource FgMuted}" Margin="24,0,0,18" FontSize="12"
                    Text="When enabled, a scan lists files inside ZIP, RAR, 7z, TAR, and similar archives from the archive catalog — files are not extracted. Individual uncompressed sizes are stored. Folder totals still use the archive’s size on disk. Online-only cloud archives are skipped."/>
+        <CheckBox x:Name="AutoIndexRemovable" Margin="0,0,0,6"
+                  Content="Automatically index removable drives when they appear"/>
+        <TextBlock TextWrapping="Wrap" Foreground="{DynamicResource FgMuted}" Margin="24,0,0,18" FontSize="12"
+                   Text="USB and other removable volumes are queued for a full scan when they come online and are not indexed yet. Cloud locations are never auto-indexed. Online-only files are not hydrated."/>
+
+        <TextBlock Text="Background host" FontSize="16" FontWeight="SemiBold" Margin="0,8,0,10"/>
+        <CheckBox x:Name="BackgroundHostAtLogon" Margin="0,0,0,6"
+                  Content="Start Explorer.Host.exe at Windows sign-in"/>
+        <TextBlock TextWrapping="Wrap" Foreground="{DynamicResource FgMuted}" Margin="24,0,0,18" FontSize="12"
+                   Text="Registers a per-user logon task. The window still owns indexing in this version. If the host starts while this window is open, it exits because the index is already in use."/>
 
         <TextBlock Text="7-Zip" FontSize="16" FontWeight="SemiBold" Margin="0,8,0,10"/>
         <TextBlock TextWrapping="Wrap" Foreground="{DynamicResource FgMuted}" Margin="0,0,0,8" FontSize="12"

src/Explorer.App/SettingsWindow.xaml.cs

@@ -1,5 +1,6 @@
 using System.Windows;
 using Explorer.Application;
+using Explorer.Hosting;
 using Explorer.Presentation.ViewModels;
 
 namespace Explorer.App;
@@ -20,6 +21,8 @@ public partial class SettingsWindow : Window
         GroupNetwork.IsChecked = prefs.GroupNetworkPlaces;
         GroupCloud.IsChecked = prefs.GroupCloudPlaces;
         IndexArchives.IsChecked = prefs.IndexArchiveContents;
+        AutoIndexRemovable.IsChecked = prefs.AutoIndexRemovable;
+        BackgroundHostAtLogon.IsChecked = prefs.BackgroundHostAtLogon;
         ShowHidden.IsChecked = prefs.ShowHiddenFiles;
         ShowProtected.IsChecked = prefs.ShowProtectedSystemLocations;
         AutoClearQueue.IsChecked = prefs.AutoClearQueueWhenDone;
@@ -45,6 +48,8 @@ public partial class SettingsWindow : Window
             GroupNetworkPlaces = GroupNetwork.IsChecked == true,
             GroupCloudPlaces = GroupCloud.IsChecked == true,
             IndexArchiveContents = IndexArchives.IsChecked == true,
+            AutoIndexRemovable = AutoIndexRemovable.IsChecked == true,
+            BackgroundHostAtLogon = BackgroundHostAtLogon.IsChecked == true,
             ShowHiddenFiles = ShowHidden.IsChecked == true,
             ShowProtectedSystemLocations = ShowProtected.IsChecked == true,
             AutoClearQueueWhenDone = AutoClearQueue.IsChecked == true,
@@ -52,10 +57,41 @@ public partial class SettingsWindow : Window
             GitPath = string.IsNullOrWhiteSpace(GitPath.Text) ? null : GitPath.Text.Trim()
         };
         await _vm.ApplyPreferencesAsync(prefs).ConfigureAwait(true);
+        ApplyBackgroundHostAutostart(prefs.BackgroundHostAtLogon);
         DialogResult = true;
         Close();
     }
 
+    private void ApplyBackgroundHostAutostart(bool enabled)
+    {
+        if (enabled)
+        {
+            var exe = HostLogonAutostart.FindHostExecutable();
+            if (exe is null)
+            {
+                MessageBox.Show(
+                    this,
+                    "Explorer.Host.exe was not found next to Explorer Workbench, so the sign-in task was not registered.",
+                    "Background host",
+                    MessageBoxButton.OK,
+                    MessageBoxImage.Warning);
+                return;
+            }
+
+            if (!HostLogonAutostart.TryRegister(exe, out var error))
+            {
+                MessageBox.Show(this, error, "Background host", MessageBoxButton.OK, MessageBoxImage.Warning);
+            }
+
+            return;
+        }
+
+        if (!HostLogonAutostart.TryUnregister(out var unregisterError))
+        {
+            MessageBox.Show(this, unregisterError, "Background host", MessageBoxButton.OK, MessageBoxImage.Warning);
+        }
+    }
+
     private void OnBrowseSevenZip(object sender, RoutedEventArgs e)
     {
         var dlg = new Microsoft.Win32.OpenFileDialog

src/Explorer.Application/IElevatedScanService.cs

@@ -1,5 +1,10 @@
 namespace Explorer.Application;
 
+/// <summary>
+/// Detects whether this process already has administrator rights.
+/// Elevation is never requested automatically. A future helper may scan USN
+/// under elevation; it must not host the transfer queue or index writer.
+/// </summary>
 public interface IElevatedScanService
 {
     bool IsElevated { get; }

src/Explorer.Application/RemovableAutoIndexPlanner.cs

@@ -0,0 +1,23 @@
+using Explorer.Domain;
+
+namespace Explorer.Application;
+
+public static class RemovableAutoIndexPlanner
+{
+    public static IReadOnlyList<long> SourceIdsToScan(IEnumerable<Source> sources, bool autoIndexRemovable)
+    {
+        if (!autoIndexRemovable)
+        {
+            return [];
+        }
+
+        return sources
+            .Where(source =>
+                source.Kind == SourceKind.Removable
+                && source.Status == SourceStatus.Online
+                && !source.IsIndexed
+                && !string.IsNullOrWhiteSpace(source.LastRootPath))
+            .Select(source => source.Id)
+            .ToList();
+    }
+}

src/Explorer.Application/UiPreferencesStore.cs

@@ -24,7 +24,9 @@ public sealed record UiPreferences(
     string? OrganizeDocuments = null,
     string? OrganizeInstallers = null,
     string? OrganizeArchives = null,
-    string? OrganizeDevelopment = null)
+    string? OrganizeDevelopment = null,
+    bool AutoIndexRemovable = false,
+    bool BackgroundHostAtLogon = false)
 {
     public static UiPreferences Default { get; } = new("Dark", false, false, false, true, false);
 }
@@ -69,6 +71,8 @@ public sealed class UiPreferencesStore
                 "show-hidden=" + (preferences.ShowHiddenFiles ? "true" : "false"),
                 "show-protected=" + (preferences.ShowProtectedSystemLocations ? "true" : "false"),
                 "auto-clear-queue=" + (preferences.AutoClearQueueWhenDone ? "true" : "false"),
+                "auto-index-removable=" + (preferences.AutoIndexRemovable ? "true" : "false"),
+                "background-host-at-logon=" + (preferences.BackgroundHostAtLogon ? "true" : "false"),
                 .. SevenZipLines(preferences),
                 .. GitLines(preferences),
                 .. OrganizeLines(preferences),
@@ -90,6 +94,8 @@ public sealed class UiPreferencesStore
         var showHidden = true;
         var showProtected = false;
         var autoClearQueue = false;
+        var autoIndexRemovable = false;
+        var backgroundHostAtLogon = false;
         string? sevenZipPath = null;
         string? gitPath = null;
         string? organizePictures = null;
@@ -149,6 +155,14 @@ public sealed class UiPreferencesStore
             {
                 autoClearQueue = IsTrue(value);
             }
+            else if (key.Equals("auto-index-removable", StringComparison.OrdinalIgnoreCase))
+            {
+                autoIndexRemovable = IsTrue(value);
+            }
+            else if (key.Equals("background-host-at-logon", StringComparison.OrdinalIgnoreCase))
+            {
+                backgroundHostAtLogon = IsTrue(value);
+            }
             else if (key.Equals("seven-zip", StringComparison.OrdinalIgnoreCase))
             {
                 sevenZipPath = string.IsNullOrWhiteSpace(value) ? null : value;
@@ -215,7 +229,7 @@ public sealed class UiPreferencesStore
             theme, groupNetwork, groupCloud, indexArchives, showHidden, showProtected, autoClearQueue,
             windowWidth, windowHeight, windowLeft, windowTop, windowMaximized, treeWidth, sevenZipPath, gitPath,
             organizePictures, organizeVideos, organizeAudio, organizeDocuments, organizeInstallers, organizeArchives,
-            organizeDevelopment);
+            organizeDevelopment, autoIndexRemovable, backgroundHostAtLogon);
     }
 
     private static IEnumerable<string> SevenZipLines(UiPreferences preferences)

src/Explorer.Application/WorkbenchHost.cs

@@ -0,0 +1,15 @@
+using Explorer.Contracts;
+
+namespace Explorer.Application;
+
+public sealed class WorkbenchHost : IWorkbenchHost
+{
+    public WorkbenchHost(IIndexingHost indexing, ITransferHost transfers)
+    {
+        Indexing = indexing;
+        Transfers = transfers;
+    }
+
+    public IIndexingHost Indexing { get; }
+    public ITransferHost Transfers { get; }
+}

src/Explorer.Contracts/IWorkbenchHost.cs

@@ -0,0 +1,36 @@
+using Explorer.Domain;
+
+namespace Explorer.Contracts;
+
+public interface IWorkbenchHost
+{
+    IIndexingHost Indexing { get; }
+    ITransferHost Transfers { get; }
+}
+
+public interface IIndexingHost
+{
+    event EventHandler<ScanProgress>? ProgressChanged;
+    void EnqueueFullScan(long sourceId);
+    void EnqueueFolderScan(long sourceId, string pathRel);
+    void EnqueueReconcile(long sourceId, string pathRel);
+    void Cancel(long sourceId);
+}
+
+public interface ITransferHost
+{
+    event EventHandler? Changed;
+    event EventHandler<TransferJob>? JobFinished;
+    bool IsPaused { get; }
+    IReadOnlyList<TransferJob> Snapshot();
+    void PauseAll();
+    void ResumeAll();
+    void Pause(long jobId);
+    void Resume(long jobId);
+    void Retry(long jobId);
+    void Cancel(long jobId);
+    void Dismiss(long jobId);
+    void ClearFinished();
+    bool MoveUp(long jobId);
+    bool MoveDown(long jobId);
+}

src/Explorer.FileOperations/Explorer.FileOperations.csproj

@@ -8,6 +8,7 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Explorer.Application\Explorer.Application.csproj" />
+    <ProjectReference Include="..\Explorer.Contracts\Explorer.Contracts.csproj" />
     <ProjectReference Include="..\Explorer.Domain\Explorer.Domain.csproj" />
   </ItemGroup>
 </Project>

src/Explorer.FileOperations/TransferQueue.cs

@@ -1,3 +1,4 @@
+using Explorer.Contracts;
 using Explorer.Domain;
 using Explorer.Domain.Abstractions;
 using Microsoft.Extensions.Hosting;
@@ -5,7 +6,7 @@ using Microsoft.Extensions.Logging;
 
 namespace Explorer.FileOperations;
 
-public sealed class TransferQueue : BackgroundService
+public sealed class TransferQueue : BackgroundService, ITransferHost
 {
     private readonly IOperationExecutor _executor;
     private readonly IIndexStore _store;

src/Explorer.Host/Explorer.Host.csproj

@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <RootNamespace>Explorer.Host</RootNamespace>
+    <AssemblyName>Explorer.Host</AssemblyName>
+    <ApplicationManifest>..\Explorer.App\app.manifest</ApplicationManifest>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.0" />
+    <PackageReference Include="Serilog" Version="4.3.0" />
+    <PackageReference Include="Serilog.Extensions.Hosting" Version="9.0.0" />
+    <PackageReference Include="Serilog.Sinks.File" Version="7.0.0" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\Explorer.Hosting\Explorer.Hosting.csproj" />
+    <ProjectReference Include="..\Explorer.Windows\Explorer.Windows.csproj" />
+  </ItemGroup>
+</Project>

src/Explorer.Host/Program.cs

@@ -0,0 +1,37 @@
+using Explorer.Hosting;
+using Explorer.Windows;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Serilog;
+
+var env = new WindowsAppEnvironment();
+Log.Logger = new LoggerConfiguration()
+    .MinimumLevel.Information()
+    .WriteTo.File(
+        Path.Combine(env.LogDirectory, "explorer-host-.log"),
+        rollingInterval: RollingInterval.Day,
+        retainedFileCountLimit: 14)
+    .CreateLogger();
+
+try
+{
+    var builder = Host.CreateApplicationBuilder(args);
+    builder.Services.AddExplorerHostProcess();
+    using var host = builder.Build();
+    await host.RunAsync().ConfigureAwait(false);
+    return 0;
+}
+catch (InvalidOperationException ex) when (ex.Message.Contains("already in use", StringComparison.OrdinalIgnoreCase))
+{
+    Log.Warning(ex, "Index store is already owned; background host exiting");
+    return 1;
+}
+catch (Exception ex)
+{
+    Log.Fatal(ex, "Explorer.Host failed");
+    return 1;
+}
+finally
+{
+    await Log.CloseAndFlushAsync().ConfigureAwait(false);
+}

src/Explorer.Hosting/Explorer.Hosting.csproj

@@ -0,0 +1,29 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <RootNamespace>Explorer.Hosting</RootNamespace>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="10.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.0" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\Explorer.Analysis\Explorer.Analysis.csproj" />
+    <ProjectReference Include="..\Explorer.Application\Explorer.Application.csproj" />
+    <ProjectReference Include="..\Explorer.Contracts\Explorer.Contracts.csproj" />
+    <ProjectReference Include="..\Explorer.Domain\Explorer.Domain.csproj" />
+    <ProjectReference Include="..\Explorer.FileOperations\Explorer.FileOperations.csproj" />
+    <ProjectReference Include="..\Explorer.Indexing\Explorer.Indexing.csproj" />
+    <ProjectReference Include="..\Explorer.Plugin.Abstractions\Explorer.Plugin.Abstractions.csproj" />
+    <ProjectReference Include="..\Explorer.Plugin.GoogleDrive\Explorer.Plugin.GoogleDrive.csproj" />
+    <ProjectReference Include="..\Explorer.Plugin.Nextcloud\Explorer.Plugin.Nextcloud.csproj" />
+    <ProjectReference Include="..\Explorer.Plugin.OneDrive\Explorer.Plugin.OneDrive.csproj" />
+    <ProjectReference Include="..\Explorer.Search\Explorer.Search.csproj" />
+    <ProjectReference Include="..\Explorer.Storage.Sqlite\Explorer.Storage.Sqlite.csproj" />
+    <ProjectReference Include="..\Explorer.Windows\Explorer.Windows.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="Explorer.Hosting.Tests" />
+  </ItemGroup>
+</Project>

src/Explorer.Hosting/ExplorerHostServices.cs

@@ -0,0 +1,100 @@
+using Explorer.Analysis;
+using Explorer.Application;
+using Explorer.Contracts;
+using Explorer.Domain;
+using Explorer.Domain.Abstractions;
+using Explorer.FileOperations;
+using Explorer.Hosting.Ipc;
+using Explorer.Indexing;
+using Explorer.Plugin.Abstractions;
+using Explorer.Plugin.GoogleDrive;
+using Explorer.Plugin.Nextcloud;
+using Explorer.Plugin.OneDrive;
+using Explorer.Search;
+using Explorer.Storage.Sqlite;
+using Explorer.Windows;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Explorer.Hosting;
+
+public static class ExplorerHostServices
+{
+    public static IServiceCollection AddExplorerCore(this IServiceCollection services)
+    {
+        services.TryAddSingleton<IClock, SystemClock>();
+        services.TryAddSingleton<IAppEnvironment, WindowsAppEnvironment>();
+        services.AddSingleton<IVolumeService, WindowsVolumeService>();
+        services.AddSingleton<IFileSystemEnumerator, WindowsFileSystemEnumerator>();
+        services.AddSingleton<IUsnJournal, WindowsUsnJournal>();
+        services.AddSingleton<IShellFileOperations, WindowsShellFileOperations>();
+        services.AddSingleton<IIndexStore>(sp =>
+        {
+            var env = sp.GetRequiredService<IAppEnvironment>();
+            var logger = sp.GetRequiredService<ILogger<SqliteIndexStore>>();
+            return new SqliteIndexStore(env.DatabasePath, logger);
+        });
+        services.AddSingleton<IStorageProvider, OneDriveStorageProvider>();
+        services.AddSingleton<IStorageProvider, GoogleDriveStorageProvider>();
+        services.AddSingleton<IStorageProvider, NextcloudStorageProvider>();
+        services.AddSingleton<StorageProviderRegistry>();
+        services.AddSingleton<IHydrationGuard, HydrationGuard>();
+        services.AddSingleton<IArchiveExecutor, SevenZipArchiveExecutor>();
+        services.AddSingleton<WindowsGitStatusProvider>();
+        services.AddSingleton<IGitStatusProvider>(sp => sp.GetRequiredService<WindowsGitStatusProvider>());
+        services.AddSingleton<IGitCommandProvider>(sp => sp.GetRequiredService<WindowsGitStatusProvider>());
+        services.AddSingleton<IElevatedScanService, WindowsElevatedScanService>();
+        services.AddSingleton<IRecycleBinCatalog, WindowsRecycleBinCatalog>();
+        services.AddSingleton<SourceManager>();
+        services.AddSingleton<PathHistoryStore>();
+        services.AddSingleton<CloudPlaceStore>();
+        services.AddSingleton<UiPreferencesStore>();
+        services.AddSingleton<IArchiveCatalog, ArchiveCatalog>();
+        services.AddSingleton<ArchiveContentsIndexer>();
+        services.AddSingleton<BrowseService>();
+        services.AddSingleton<FilesystemScanner>();
+        services.AddSingleton<FolderReconciler>();
+        services.AddSingleton<UsnChangeApplier>();
+        services.AddSingleton<IndexingCoordinator>();
+        services.AddSingleton<DirectoryWatcherHub>();
+        services.AddSingleton<SearchService>();
+        services.AddSingleton<AnalysisService>();
+        services.AddSingleton<IOperationExecutor, NativeFileOperationExecutor>();
+        services.AddSingleton<TransferQueue>();
+        services.AddSingleton<ITransferHost>(sp => sp.GetRequiredService<TransferQueue>());
+        services.AddSingleton<IIndexingHost>(sp => sp.GetRequiredService<IndexingCoordinator>());
+        services.AddSingleton<IWorkbenchHost, WorkbenchHost>();
+        services.AddSingleton<FileOperationService>();
+        services.AddSingleton<RenamePlanner>();
+        services.AddSingleton<RenameBatchService>();
+        services.AddSingleton<FolderSyncPlanner>();
+        services.AddSingleton<FolderSyncService>();
+        services.AddSingleton<FileOperationProfilePlanner>();
+        services.AddSingleton<OperationProfileService>();
+        services.AddSingleton<ReorganizePlanner>();
+        services.AddSingleton<ReorganizeService>();
+        services.AddSingleton<DuplicateHashWorker>();
+        services.AddSingleton<HistoryRollupService>();
+        services.AddHostedService(sp => sp.GetRequiredService<IndexingCoordinator>());
+        services.AddHostedService(sp => sp.GetRequiredService<TransferQueue>());
+        services.AddHostedService(sp => sp.GetRequiredService<DuplicateHashWorker>());
+        services.AddHostedService(sp => sp.GetRequiredService<HistoryRollupService>());
+        services.AddHostedService<WatcherHostedService>();
+        return services;
+    }
+
+    /// <summary>
+    /// Registers the background host process: open the store first, then Core workers, then the named pipe.
+    /// Do not call this from the GUI while the GUI still opens the index for write.
+    /// </summary>
+    public static IServiceCollection AddExplorerHostProcess(this IServiceCollection services)
+    {
+        services.TryAddSingleton<WorkbenchIpcOptions>();
+        services.AddHostedService<IndexStoreLifetime>();
+        services.AddExplorerCore();
+        services.AddHostedService<WorkbenchPipeServer>();
+        return services;
+    }
+}

src/Explorer.Hosting/HostLogonAutostart.cs

@@ -0,0 +1,109 @@
+using System.Diagnostics;
+
+namespace Explorer.Hosting;
+
+public static class HostLogonAutostart
+{
+    public const string TaskName = "ExplorerWorkbenchHost";
+
+    public static string? FindHostExecutable()
+    {
+        var candidate = Path.Combine(AppContext.BaseDirectory, "Explorer.Host.exe");
+        return File.Exists(candidate) ? candidate : null;
+    }
+
+    public static string[] CreateTaskArgs(string hostExePath)
+        =>
+        [
+            "/Create",
+            "/TN",
+            TaskName,
+            "/TR",
+            Quote(hostExePath),
+            "/SC",
+            "ONLOGON",
+            "/F",
+            "/RL",
+            "LIMITED"
+        ];
+
+    public static string[] DeleteTaskArgs() => ["/Delete", "/TN", TaskName, "/F"];
+
+    public static bool TryRegister(string hostExePath, out string error)
+    {
+        if (!File.Exists(hostExePath))
+        {
+            error = "Explorer.Host.exe was not found next to Explorer Workbench.";
+            return false;
+        }
+
+        return Run(CreateTaskArgs(hostExePath), out error);
+    }
+
+    public static bool TryUnregister(out string error) => Run(DeleteTaskArgs(), out error);
+
+    private static string Quote(string path) => "\"" + path + "\"";
+
+    private static bool Run(string[] args, out string error)
+    {
+        try
+        {
+            using var process = new Process
+            {
+                StartInfo = new ProcessStartInfo
+                {
+                    FileName = "schtasks.exe",
+                    UseShellExecute = false,
+                    CreateNoWindow = true,
+                    RedirectStandardOutput = true,
+                    RedirectStandardError = true
+                }
+            };
+            foreach (var arg in args)
+            {
+                process.StartInfo.ArgumentList.Add(arg);
+            }
+
+            process.Start();
+            if (!process.WaitForExit(8000))
+            {
+                try { process.Kill(entireProcessTree: true); } catch { /* ignore */ }
+                error = "Timed out updating the sign-in task.";
+                return false;
+            }
+
+            var stderr = process.StandardError.ReadToEnd();
+            var stdout = process.StandardOutput.ReadToEnd();
+            if (process.ExitCode != 0)
+            {
+                error = string.IsNullOrWhiteSpace(stderr) ? stdout : stderr;
+                if (IsAlreadyAbsent(args, error))
+                {
+                    error = "";
+                    return true;
+                }
+
+                if (string.IsNullOrWhiteSpace(error))
+                {
+                    error = "schtasks exited with code " + process.ExitCode;
+                }
+
+                return false;
+            }
+
+            error = "";
+            return true;
+        }
+        catch (Exception ex)
+        {
+            error = ex.Message;
+            return false;
+        }
+    }
+
+    private static bool IsAlreadyAbsent(string[] args, string error)
+        => args.Length > 0
+           && args[0].Equals("/Delete", StringComparison.OrdinalIgnoreCase)
+           && (error.Contains("cannot find", StringComparison.OrdinalIgnoreCase)
+               || error.Contains("not found", StringComparison.OrdinalIgnoreCase));
+}

src/Explorer.Hosting/IndexStoreLifetime.cs

@@ -0,0 +1,15 @@
+using Explorer.Domain.Abstractions;
+using Microsoft.Extensions.Hosting;
+
+namespace Explorer.Hosting;
+
+public sealed class IndexStoreLifetime : IHostedService
+{
+    private readonly IIndexStore _store;
+
+    public IndexStoreLifetime(IIndexStore store) => _store = store;
+
+    public Task StartAsync(CancellationToken cancellationToken) => _store.OpenAsync(cancellationToken);
+
+    public Task StopAsync(CancellationToken cancellationToken) => _store.CloseAsync();
+}

src/Explorer.Hosting/Ipc/WorkbenchIpc.cs

@@ -0,0 +1,48 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Explorer.Domain;
+
+namespace Explorer.Hosting.Ipc;
+
+public sealed class WorkbenchIpcOptions
+{
+    public string PipeName { get; set; } = WorkbenchIpc.DefaultPipeName;
+}
+
+public static class WorkbenchIpc
+{
+    public const int ProtocolVersion = 1;
+
+    public static string DefaultPipeName { get; } = Sanitize("ExplorerWorkbench-" + Environment.UserName);
+
+    public static JsonSerializerOptions Json { get; } = new()
+    {
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        PropertyNameCaseInsensitive = true,
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        Converters = { new JsonStringEnumConverter(JsonNamingPolicy.CamelCase) }
+    };
+
+    public static string Sanitize(string name)
+    {
+        var chars = name.Select(c => char.IsLetterOrDigit(c) || c is '-' or '_' ? c : '-').ToArray();
+        return new string(chars);
+    }
+}
+
+internal sealed class IpcEnvelope
+{
+    public int V { get; set; } = WorkbenchIpc.ProtocolVersion;
+    public string? Id { get; set; }
+    public string? Op { get; set; }
+    public string? Evt { get; set; }
+    public bool? Ok { get; set; }
+    public string? Error { get; set; }
+    public long? N { get; set; }
+    public string? S { get; set; }
+    public bool? Flag { get; set; }
+    public bool? Paused { get; set; }
+    public ScanProgress? Progress { get; set; }
+    public TransferJob? Job { get; set; }
+    public TransferJob[]? Jobs { get; set; }
+}

src/Explorer.Hosting/Ipc/WorkbenchPipeClient.cs

@@ -0,0 +1,276 @@
+using System.Collections.Concurrent;
+using System.IO.Pipes;
+using System.Text;
+using System.Text.Json;
+using Explorer.Contracts;
+using Explorer.Domain;
+
+namespace Explorer.Hosting.Ipc;
+
+public sealed class WorkbenchPipeClient : IWorkbenchHost, IAsyncDisposable
+{
+    private readonly NamedPipeClientStream _pipe;
+    private readonly StreamWriter _writer;
+    private readonly StreamReader _reader;
+    private readonly SemaphoreSlim _send = new(1, 1);
+    private readonly ConcurrentDictionary<string, TaskCompletionSource<IpcEnvelope>> _pending = new();
+    private readonly CancellationTokenSource _cts = new();
+    private readonly Task _readLoop;
+    private readonly IndexingProxy _indexing;
+    private readonly TransferProxy _transfers;
+
+    private WorkbenchPipeClient(NamedPipeClientStream pipe)
+    {
+        _pipe = pipe;
+        _writer = new StreamWriter(pipe, Encoding.UTF8, leaveOpen: true) { AutoFlush = true, NewLine = "\n" };
+        _reader = new StreamReader(pipe, Encoding.UTF8, detectEncodingFromByteOrderMarks: false, leaveOpen: true);
+        _indexing = new IndexingProxy(this);
+        _transfers = new TransferProxy(this);
+        _readLoop = ReadLoopAsync(_cts.Token);
+    }
+
+    public IIndexingHost Indexing => _indexing;
+    public ITransferHost Transfers => _transfers;
+
+    public static async Task<WorkbenchPipeClient> ConnectAsync(
+        WorkbenchIpcOptions options,
+        TimeSpan timeout,
+        CancellationToken cancellationToken = default)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        Exception? last = null;
+        while (DateTime.UtcNow < deadline)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            var pipe = new NamedPipeClientStream(
+                ".",
+                options.PipeName,
+                PipeDirection.InOut,
+                PipeOptions.Asynchronous);
+            try
+            {
+                var remaining = deadline - DateTime.UtcNow;
+                if (remaining < TimeSpan.FromMilliseconds(50))
+                {
+                    remaining = TimeSpan.FromMilliseconds(50);
+                }
+
+                await pipe.ConnectAsync(remaining, cancellationToken).ConfigureAwait(false);
+                var client = new WorkbenchPipeClient(pipe);
+                await client.CallAsync("Ping", cancellationToken).ConfigureAwait(false);
+                return client;
+            }
+            catch (Exception ex) when (ex is not OperationCanceledException)
+            {
+                last = ex;
+                await pipe.DisposeAsync().ConfigureAwait(false);
+                try
+                {
+                    await Task.Delay(80, cancellationToken).ConfigureAwait(false);
+                }
+                catch (OperationCanceledException)
+                {
+                    throw;
+                }
+            }
+        }
+
+        throw new TimeoutException(
+            $"Could not connect to Explorer Workbench host pipe '{options.PipeName}'.", last);
+    }
+
+    internal IpcEnvelope Call(string op, long? n = null, string? s = null)
+        => CallAsync(op, CancellationToken.None, n, s).GetAwaiter().GetResult();
+
+    internal async Task<IpcEnvelope> CallAsync(
+        string op,
+        CancellationToken cancellationToken,
+        long? n = null,
+        string? s = null)
+    {
+        var id = Guid.NewGuid().ToString("N");
+        var tcs = new TaskCompletionSource<IpcEnvelope>(TaskCreationOptions.RunContinuationsAsynchronously);
+        _pending[id] = tcs;
+        var request = new IpcEnvelope { V = WorkbenchIpc.ProtocolVersion, Id = id, Op = op, N = n, S = s };
+        var json = JsonSerializer.Serialize(request, WorkbenchIpc.Json);
+        await _send.WaitAsync(cancellationToken).ConfigureAwait(false);
+        try
+        {
+            await _writer.WriteLineAsync(json.AsMemory(), cancellationToken).ConfigureAwait(false);
+        }
+        catch
+        {
+            _pending.TryRemove(id, out _);
+            throw;
+        }
+        finally
+        {
+            _send.Release();
+        }
+
+        using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(15));
+        using var linked = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeout.Token, _cts.Token);
+        using var cancelReg = linked.Token.Register(() => tcs.TrySetCanceled(linked.Token));
+        try
+        {
+            var reply = await tcs.Task.ConfigureAwait(false);
+            if (reply.Ok == false)
+            {
+                throw new InvalidOperationException(reply.Error ?? "Host call failed.");
+            }
+
+            return reply;
+        }
+        finally
+        {
+            _pending.TryRemove(id, out _);
+        }
+    }
+
+    internal void RaiseProgress(ScanProgress progress) => _indexing.Raise(progress);
+    internal void RaiseChanged() => _transfers.RaiseChanged();
+    internal void RaiseFinished(TransferJob job) => _transfers.RaiseFinished(job);
+
+    private async Task ReadLoopAsync(CancellationToken cancellationToken)
+    {
+        try
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                var line = await _reader.ReadLineAsync(cancellationToken).ConfigureAwait(false);
+                if (line is null)
+                {
+                    break;
+                }
+
+                if (string.IsNullOrWhiteSpace(line))
+                {
+                    continue;
+                }
+
+                IpcEnvelope? envelope;
+                try
+                {
+                    envelope = JsonSerializer.Deserialize<IpcEnvelope>(line, WorkbenchIpc.Json);
+                }
+                catch (JsonException)
+                {
+                    continue;
+                }
+
+                if (envelope is null)
+                {
+                    continue;
+                }
+
+                if (!string.IsNullOrEmpty(envelope.Evt))
+                {
+                    switch (envelope.Evt)
+                    {
+                        case "Indexing.Progress" when envelope.Progress is not null:
+                            RaiseProgress(envelope.Progress);
+                            break;
+                        case "Transfers.Changed":
+                            RaiseChanged();
+                            break;
+                        case "Transfers.JobFinished" when envelope.Job is not null:
+                            RaiseFinished(envelope.Job);
+                            break;
+                    }
+
+                    continue;
+                }
+
+                if (envelope.Id is not null && _pending.TryRemove(envelope.Id, out var tcs))
+                {
+                    tcs.TrySetResult(envelope);
+                }
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            // shutting down
+        }
+        finally
+        {
+            foreach (var tcs in _pending.Values)
+            {
+                tcs.TrySetCanceled(cancellationToken);
+            }
+        }
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await _cts.CancelAsync().ConfigureAwait(false);
+        try
+        {
+            await _writer.DisposeAsync().ConfigureAwait(false);
+        }
+        catch
+        {
+            // pipe already closed
+        }
+
+        _reader.Dispose();
+        await _pipe.DisposeAsync().ConfigureAwait(false);
+        try
+        {
+            await _readLoop.WaitAsync(TimeSpan.FromSeconds(2)).ConfigureAwait(false);
+        }
+        catch (TimeoutException)
+        {
+            // reader may still be unwinding after the pipe close
+        }
+        catch (OperationCanceledException)
+        {
+            // expected
+        }
+
+        _cts.Dispose();
+        _send.Dispose();
+    }
+
+    private sealed class IndexingProxy : IIndexingHost
+    {
+        private readonly WorkbenchPipeClient _client;
+        public event EventHandler<ScanProgress>? ProgressChanged = delegate { };
+
+        public IndexingProxy(WorkbenchPipeClient client) => _client = client;
+
+        public void EnqueueFullScan(long sourceId) => _client.Call("Indexing.EnqueueFullScan", sourceId);
+        public void EnqueueFolderScan(long sourceId, string pathRel)
+            => _client.Call("Indexing.EnqueueFolderScan", sourceId, pathRel);
+        public void EnqueueReconcile(long sourceId, string pathRel)
+            => _client.Call("Indexing.EnqueueReconcile", sourceId, pathRel);
+        public void Cancel(long sourceId) => _client.Call("Indexing.Cancel", sourceId);
+        public void Raise(ScanProgress progress) => ProgressChanged?.Invoke(this, progress);
+    }
+
+    private sealed class TransferProxy : ITransferHost
+    {
+        private readonly WorkbenchPipeClient _client;
+        public event EventHandler? Changed = delegate { };
+        public event EventHandler<TransferJob>? JobFinished = delegate { };
+
+        public TransferProxy(WorkbenchPipeClient client) => _client = client;
+
+        public bool IsPaused => _client.Call("Transfers.IsPaused").Paused == true;
+
+        public IReadOnlyList<TransferJob> Snapshot()
+            => _client.Call("Transfers.Snapshot").Jobs ?? [];
+
+        public void PauseAll() => _client.Call("Transfers.PauseAll");
+        public void ResumeAll() => _client.Call("Transfers.ResumeAll");
+        public void Pause(long jobId) => _client.Call("Transfers.Pause", jobId);
+        public void Resume(long jobId) => _client.Call("Transfers.Resume", jobId);
+        public void Retry(long jobId) => _client.Call("Transfers.Retry", jobId);
+        public void Cancel(long jobId) => _client.Call("Transfers.Cancel", jobId);
+        public void Dismiss(long jobId) => _client.Call("Transfers.Dismiss", jobId);
+        public void ClearFinished() => _client.Call("Transfers.ClearFinished");
+        public bool MoveUp(long jobId) => _client.Call("Transfers.MoveUp", jobId).Flag == true;
+        public bool MoveDown(long jobId) => _client.Call("Transfers.MoveDown", jobId).Flag == true;
+        public void RaiseChanged() => Changed?.Invoke(this, EventArgs.Empty);
+        public void RaiseFinished(TransferJob job) => JobFinished?.Invoke(this, job);
+    }
+}

src/Explorer.Hosting/Ipc/WorkbenchPipeServer.cs

@@ -0,0 +1,233 @@
+using System.IO.Pipes;
+using System.Text;
+using System.Text.Json;
+using Explorer.Contracts;
+using Explorer.Domain;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Explorer.Hosting.Ipc;
+
+public sealed class WorkbenchPipeServer : BackgroundService
+{
+    private readonly IWorkbenchHost _workbench;
+    private readonly WorkbenchIpcOptions _options;
+    private readonly ILogger<WorkbenchPipeServer> _logger;
+    private readonly SemaphoreSlim _write = new(1, 1);
+    private readonly TaskCompletionSource _listening = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+    public WorkbenchPipeServer(
+        IWorkbenchHost workbench,
+        WorkbenchIpcOptions options,
+        ILogger<WorkbenchPipeServer> logger)
+    {
+        _workbench = workbench;
+        _options = options;
+        _logger = logger;
+    }
+
+    public Task Listening => _listening.Task;
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("Listening on named pipe {Pipe} protocol v{Version}", _options.PipeName, WorkbenchIpc.ProtocolVersion);
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                var server = new NamedPipeServerStream(
+                    _options.PipeName,
+                    PipeDirection.InOut,
+                    1,
+                    PipeTransmissionMode.Byte,
+                    PipeOptions.Asynchronous);
+                await using (server.ConfigureAwait(false))
+                {
+                    _listening.TrySetResult();
+                    using var cancelPipe = stoppingToken.Register(() =>
+                    {
+                        try { server.Dispose(); }
+                        catch (ObjectDisposedException) { }
+                        catch (IOException) { }
+                    });
+                    await server.WaitForConnectionAsync(stoppingToken).ConfigureAwait(false);
+                    await ServeAsync(server, stoppingToken).ConfigureAwait(false);
+                }
+            }
+            catch (ObjectDisposedException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (IOException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Workbench pipe session ended");
+                try
+                {
+                    await Task.Delay(250, stoppingToken).ConfigureAwait(false);
+                }
+                catch (OperationCanceledException)
+                {
+                    break;
+                }
+            }
+        }
+    }
+
+    private async Task ServeAsync(NamedPipeServerStream pipe, CancellationToken stoppingToken)
+    {
+        using var reader = new StreamReader(pipe, Encoding.UTF8, detectEncodingFromByteOrderMarks: false, leaveOpen: true);
+        await using var writer = new StreamWriter(pipe, Encoding.UTF8, leaveOpen: true) { AutoFlush = true, NewLine = "\n" };
+
+        void OnProgress(object? sender, ScanProgress progress)
+            => _ = WriteAsync(writer, new IpcEnvelope { Evt = "Indexing.Progress", Progress = progress }, stoppingToken);
+
+        void OnChanged(object? sender, EventArgs e)
+            => _ = WriteAsync(writer, new IpcEnvelope { Evt = "Transfers.Changed" }, stoppingToken);
+
+        void OnFinished(object? sender, TransferJob job)
+            => _ = WriteAsync(writer, new IpcEnvelope { Evt = "Transfers.JobFinished", Job = job }, stoppingToken);
+
+        _workbench.Indexing.ProgressChanged += OnProgress;
+        _workbench.Transfers.Changed += OnChanged;
+        _workbench.Transfers.JobFinished += OnFinished;
+        try
+        {
+            while (!stoppingToken.IsCancellationRequested)
+            {
+                var line = await reader.ReadLineAsync(stoppingToken).ConfigureAwait(false);
+                if (line is null)
+                {
+                    break;
+                }
+
+                if (string.IsNullOrWhiteSpace(line))
+                {
+                    continue;
+                }
+
+                IpcEnvelope request;
+                try
+                {
+                    request = JsonSerializer.Deserialize<IpcEnvelope>(line, WorkbenchIpc.Json)
+                        ?? new IpcEnvelope { Ok = false, Error = "empty" };
+                }
+                catch (JsonException ex)
+                {
+                    await WriteAsync(writer, new IpcEnvelope { Ok = false, Error = ex.Message }, stoppingToken)
+                        .ConfigureAwait(false);
+                    continue;
+                }
+
+                var response = Handle(request);
+                await WriteAsync(writer, response, stoppingToken).ConfigureAwait(false);
+            }
+        }
+        finally
+        {
+            _workbench.Indexing.ProgressChanged -= OnProgress;
+            _workbench.Transfers.Changed -= OnChanged;
+            _workbench.Transfers.JobFinished -= OnFinished;
+        }
+    }
+
+    internal IpcEnvelope Handle(IpcEnvelope request)
+    {
+        var reply = new IpcEnvelope { Id = request.Id, Ok = true };
+        if (request.V != WorkbenchIpc.ProtocolVersion)
+        {
+            reply.Ok = false;
+            reply.Error = $"Unsupported protocol {request.V}; expected {WorkbenchIpc.ProtocolVersion}.";
+            return reply;
+        }
+
+        try
+        {
+            switch (request.Op)
+            {
+                case "Ping":
+                    return reply;
+                case "Indexing.EnqueueFullScan":
+                    _workbench.Indexing.EnqueueFullScan(request.N ?? 0);
+                    return reply;
+                case "Indexing.EnqueueFolderScan":
+                    _workbench.Indexing.EnqueueFolderScan(request.N ?? 0, request.S ?? "");
+                    return reply;
+                case "Indexing.EnqueueReconcile":
+                    _workbench.Indexing.EnqueueReconcile(request.N ?? 0, request.S ?? "");
+                    return reply;
+                case "Indexing.Cancel":
+                    _workbench.Indexing.Cancel(request.N ?? 0);
+                    return reply;
+                case "Transfers.Snapshot":
+                    reply.Jobs = _workbench.Transfers.Snapshot().ToArray();
+                    reply.Paused = _workbench.Transfers.IsPaused;
+                    return reply;
+                case "Transfers.IsPaused":
+                    reply.Paused = _workbench.Transfers.IsPaused;
+                    return reply;
+                case "Transfers.PauseAll":
+                    _workbench.Transfers.PauseAll();
+                    return reply;
+                case "Transfers.ResumeAll":
+                    _workbench.Transfers.ResumeAll();
+                    return reply;
+                case "Transfers.Pause":
+                    _workbench.Transfers.Pause(request.N ?? 0);
+                    return reply;
+                case "Transfers.Resume":
+                    _workbench.Transfers.Resume(request.N ?? 0);
+                    return reply;
+                case "Transfers.Retry":
+                    _workbench.Transfers.Retry(request.N ?? 0);
+                    return reply;
+                case "Transfers.Cancel":
+                    _workbench.Transfers.Cancel(request.N ?? 0);
+                    return reply;
+                case "Transfers.Dismiss":
+                    _workbench.Transfers.Dismiss(request.N ?? 0);
+                    return reply;
+                case "Transfers.ClearFinished":
+                    _workbench.Transfers.ClearFinished();
+                    return reply;
+                case "Transfers.MoveUp":
+                    reply.Flag = _workbench.Transfers.MoveUp(request.N ?? 0);
+                    return reply;
+                case "Transfers.MoveDown":
+                    reply.Flag = _workbench.Transfers.MoveDown(request.N ?? 0);
+                    return reply;
+                default:
+                    reply.Ok = false;
+                    reply.Error = "Unknown op " + request.Op;
+                    return reply;
+            }
+        }
+        catch (Exception ex)
+        {
+            reply.Ok = false;
+            reply.Error = ex.Message;
+            return reply;
+        }
+    }
+
+    private async Task WriteAsync(StreamWriter writer, IpcEnvelope envelope, CancellationToken cancellationToken)
+    {
+        var json = JsonSerializer.Serialize(envelope, WorkbenchIpc.Json);
+        await _write.WaitAsync(cancellationToken).ConfigureAwait(false);
+        try
+        {
+            await writer.WriteLineAsync(json.AsMemory(), cancellationToken).ConfigureAwait(false);
+        }
+        finally
+        {
+            _write.Release();
+        }
+    }
+}

src/Explorer.Hosting/WatcherHostedService.cs

@@ -0,0 +1,65 @@
+using Explorer.Application;
+using Explorer.Contracts;
+using Explorer.Domain.Abstractions;
+using Explorer.FileOperations;
+using Explorer.Indexing;
+using Microsoft.Extensions.Hosting;
+
+namespace Explorer.Hosting;
+
+public sealed class WatcherHostedService : BackgroundService
+{
+    private readonly DirectoryWatcherHub _hub;
+    private readonly SourceManager _sources;
+    private readonly TransferQueue _transfers;
+    private readonly FolderSyncService _sync;
+    private readonly OperationProfileService _profiles;
+    private readonly IIndexStore _store;
+    private readonly IIndexingHost _indexing;
+    private readonly UiPreferencesStore _preferences;
+
+    public WatcherHostedService(
+        DirectoryWatcherHub hub,
+        SourceManager sources,
+        TransferQueue transfers,
+        FolderSyncService sync,
+        OperationProfileService profiles,
+        IIndexStore store,
+        IIndexingHost indexing,
+        UiPreferencesStore preferences)
+    {
+        _hub = hub;
+        _sources = sources;
+        _transfers = transfers;
+        _sync = sync;
+        _profiles = profiles;
+        _store = store;
+        _indexing = indexing;
+        _preferences = preferences;
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        using var timer = new PeriodicTimer(TimeSpan.FromSeconds(20));
+        await _hub.RefreshAsync(stoppingToken).ConfigureAwait(false);
+        while (await timer.WaitForNextTickAsync(stoppingToken).ConfigureAwait(false))
+        {
+            await _sources.RefreshOnlineStateAsync(forceRefresh: true, stoppingToken).ConfigureAwait(false);
+            _transfers.NotifyAvailability();
+            await TryAutoIndexRemovableAsync(stoppingToken).ConfigureAwait(false);
+            await _sync.TryAutoRunAsync(stoppingToken).ConfigureAwait(false);
+            await _profiles.TryAutoRunAsync(stoppingToken).ConfigureAwait(false);
+            await _hub.RefreshAsync(stoppingToken).ConfigureAwait(false);
+        }
+    }
+
+    private async Task TryAutoIndexRemovableAsync(CancellationToken cancellationToken)
+    {
+        var prefs = _preferences.Load();
+        var sources = await _store.Sources.GetAllAsync(cancellationToken).ConfigureAwait(false);
+        foreach (var sourceId in RemovableAutoIndexPlanner.SourceIdsToScan(sources, prefs.AutoIndexRemovable))
+        {
+            _indexing.EnqueueFullScan(sourceId);
+        }
+    }
+}

src/Explorer.Indexing/Explorer.Indexing.csproj

@@ -9,6 +9,7 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Explorer.Application\Explorer.Application.csproj" />
+    <ProjectReference Include="..\Explorer.Contracts\Explorer.Contracts.csproj" />
     <ProjectReference Include="..\Explorer.Domain\Explorer.Domain.csproj" />
   </ItemGroup>
 </Project>

src/Explorer.Indexing/IndexingCoordinator.cs

@@ -1,4 +1,5 @@
 using System.Threading.Channels;
+using Explorer.Contracts;
 using Explorer.Domain;
 using Explorer.Domain.Abstractions;
 using Microsoft.Extensions.Hosting;
@@ -6,7 +7,7 @@ using Microsoft.Extensions.Logging;
 
 namespace Explorer.Indexing;
 
-public sealed class IndexingCoordinator : BackgroundService
+public sealed class IndexingCoordinator : BackgroundService, IIndexingHost
 {
     private readonly IIndexStore _store;
     private readonly FilesystemScanner _scanner;

src/Explorer.Presentation/Explorer.Presentation.csproj

@@ -10,9 +10,9 @@
   <ItemGroup>
     <ProjectReference Include="..\Explorer.Analysis\Explorer.Analysis.csproj" />
     <ProjectReference Include="..\Explorer.Application\Explorer.Application.csproj" />
+    <ProjectReference Include="..\Explorer.Contracts\Explorer.Contracts.csproj" />
     <ProjectReference Include="..\Explorer.Domain\Explorer.Domain.csproj" />
     <ProjectReference Include="..\Explorer.FileOperations\Explorer.FileOperations.csproj" />
-    <ProjectReference Include="..\Explorer.Indexing\Explorer.Indexing.csproj" />
     <ProjectReference Include="..\Explorer.Plugin.Abstractions\Explorer.Plugin.Abstractions.csproj" />
     <ProjectReference Include="..\Explorer.Search\Explorer.Search.csproj" />
   </ItemGroup>

src/Explorer.Presentation/ViewModels/ExplorerPaneViewModel.cs

@@ -2,9 +2,9 @@ using System.Collections.ObjectModel;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using Explorer.Application;
+using Explorer.Contracts;
 using Explorer.Domain;
 using Explorer.FileOperations;
-using Explorer.Indexing;
 
 namespace Explorer.Presentation.ViewModels;
 
@@ -12,7 +12,7 @@ public sealed partial class ExplorerPaneViewModel : ObservableObject
 {
     private readonly BrowseService _browse;
     private readonly FileOperationService _ops;
-    private readonly IndexingCoordinator _indexing;
+    private readonly IIndexingHost _indexing;
     private readonly SourceManager _sources;
     private readonly IGitStatusProvider _git;
     private readonly IThumbnailService? _thumbnails;
@@ -43,7 +43,7 @@ public sealed partial class ExplorerPaneViewModel : ObservableObject
     public ExplorerPaneViewModel(
         BrowseService browse,
         FileOperationService ops,
-        IndexingCoordinator indexing,
+        IIndexingHost indexing,
         SourceManager sources,
         IGitStatusProvider git,
         IThumbnailService? thumbnails = null)

src/Explorer.Presentation/ViewModels/ExplorerTabViewModel.cs

@@ -1,8 +1,8 @@
 using CommunityToolkit.Mvvm.ComponentModel;
 using Explorer.Application;
+using Explorer.Contracts;
 using Explorer.Domain;
 using Explorer.FileOperations;
-using Explorer.Indexing;
 
 namespace Explorer.Presentation.ViewModels;
 
@@ -22,7 +22,7 @@ public sealed partial class ExplorerTabViewModel : ObservableObject
     public ExplorerTabViewModel(
         BrowseService browse,
         FileOperationService ops,
-        IndexingCoordinator indexing,
+        IIndexingHost indexing,
         SourceManager sources,
         IGitStatusProvider git,
         IThumbnailService? thumbnails = null)

src/Explorer.Presentation/ViewModels/MainViewModel.cs

@@ -2,9 +2,9 @@ using System.Collections.ObjectModel;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using Explorer.Application;
+using Explorer.Contracts;
 using Explorer.Domain;
 using Explorer.FileOperations;
-using Explorer.Indexing;
 using Explorer.Search;
 using Explorer.Analysis;
 using Explorer.Domain.Abstractions;
@@ -16,7 +16,7 @@ public sealed partial class MainViewModel : ObservableObject
 {
     private readonly BrowseService _browse;
     private readonly FileOperationService _ops;
-    private readonly IndexingCoordinator _indexing;
+    private readonly IIndexingHost _indexing;
     private readonly SourceManager _sources;
     private readonly PathHistoryStore _pathHistory;
     private readonly StorageProviderRegistry _providers;
@@ -63,12 +63,11 @@ public sealed partial class MainViewModel : ObservableObject
     public MainViewModel(
         BrowseService browse,
         FileOperationService ops,
-        IndexingCoordinator indexing,
         SourceManager sources,
         SearchService search,
         AnalysisService analysis,
         IIndexStore store,
-        TransferQueue transfers,
+        IWorkbenchHost workbench,
         IOsClipboard clipboard,
         PathHistoryStore pathHistory,
         StorageProviderRegistry providers,
@@ -88,7 +87,7 @@ public sealed partial class MainViewModel : ObservableObject
     {
         _browse = browse;
         _ops = ops;
-        _indexing = indexing;
+        _indexing = workbench.Indexing;
         _sources = sources;
         _pathHistory = pathHistory;
         _providers = providers;
@@ -112,10 +111,10 @@ public sealed partial class MainViewModel : ObservableObject
         Analysis = new AnalysisViewModel(analysis);
         Duplicates = new DuplicateViewModel(store, sources, analysis);
         Duplicates.RevealPath += (_, path) => _ = RevealDuplicateAsync(path);
-        Transfers = new TransferQueueViewModel(transfers, preferences);
+        Transfers = new TransferQueueViewModel(workbench.Transfers, preferences);
         Tabs = [];
         Clipboard = clipboard;
-        transfers.JobFinished += (_, job) =>
+        workbench.Transfers.JobFinished += (_, job) =>
         {
             void Go() => _ = OnTransferFinishedAsync(job);
             if (_ui is { } ctx)

src/Explorer.Presentation/ViewModels/TransferQueueViewModel.cs

@@ -2,8 +2,8 @@ using System.Collections.ObjectModel;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using Explorer.Application;
+using Explorer.Contracts;
 using Explorer.Domain;
-using Explorer.FileOperations;
 
 namespace Explorer.Presentation.ViewModels;
 
@@ -186,7 +186,7 @@ public sealed partial class TransferJobViewModel : ObservableObject
 
 public sealed partial class TransferQueueViewModel : ObservableObject
 {
-    private readonly TransferQueue _queue;
+    private readonly ITransferHost _queue;
     private readonly UiPreferencesStore _preferences;
     private readonly SynchronizationContext? _ui = SynchronizationContext.Current;
     private readonly Dictionary<long, (long Bytes, DateTime Utc)> _speed = [];
@@ -205,7 +205,7 @@ public sealed partial class TransferQueueViewModel : ObservableObject
     [ObservableProperty] private double _overallProgress;
     [ObservableProperty] private bool _hasOverallProgress;
 
-    public TransferQueueViewModel(TransferQueue queue, UiPreferencesStore preferences)
+    public TransferQueueViewModel(ITransferHost queue, UiPreferencesStore preferences)
     {
         _queue = queue;
         _preferences = preferences;

src/Explorer.Storage.Sqlite/IndexStoreLock.cs

@@ -0,0 +1,88 @@
+using System.Collections.Concurrent;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace Explorer.Storage.Sqlite;
+
+/// <summary>
+/// Per-user lock so only one process (and one in-process owner) can open the index for write.
+/// GUI and Explorer.Host.exe must not share a writer. Named mutex recovers from a crashed owner;
+/// an in-process table stops the same thread re-entering the mutex.
+/// </summary>
+public sealed class IndexStoreLock : IDisposable
+{
+    private static readonly ConcurrentDictionary<string, byte> InProcessOwners = new(StringComparer.Ordinal);
+
+    private readonly Mutex _mutex;
+    private readonly string _name;
+    private bool _owned;
+
+    private IndexStoreLock(Mutex mutex, string name)
+    {
+        _mutex = mutex;
+        _name = name;
+        _owned = true;
+    }
+
+    public static string MutexNameFor(string databasePath)
+    {
+        var full = Path.GetFullPath(databasePath);
+        var hash = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(full.ToUpperInvariant())))[..16];
+        return @"Local\ExplorerWorkbench-Index-" + hash;
+    }
+
+    public static IndexStoreLock Acquire(string databasePath, TimeSpan? timeout = null)
+    {
+        var name = MutexNameFor(databasePath);
+        if (!InProcessOwners.TryAdd(name, 0))
+        {
+            throw new InvalidOperationException(
+                "The Explorer Workbench index is already in use by another process.");
+        }
+
+        var mutex = new Mutex(false, name);
+        var wait = timeout ?? TimeSpan.Zero;
+        try
+        {
+            if (!mutex.WaitOne(wait))
+            {
+                mutex.Dispose();
+                InProcessOwners.TryRemove(name, out _);
+                throw new InvalidOperationException(
+                    "The Explorer Workbench index is already in use by another process.");
+            }
+        }
+        catch (AbandonedMutexException)
+        {
+            // Previous owner crashed; this process now owns the mutex.
+        }
+        catch
+        {
+            mutex.Dispose();
+            InProcessOwners.TryRemove(name, out _);
+            throw;
+        }
+
+        return new IndexStoreLock(mutex, name);
+    }
+
+    public void Dispose()
+    {
+        if (_owned)
+        {
+            try
+            {
+                _mutex.ReleaseMutex();
+            }
+            catch (ApplicationException)
+            {
+                // Already released or not owned.
+            }
+
+            _owned = false;
+            InProcessOwners.TryRemove(_name, out _);
+        }
+
+        _mutex.Dispose();
+    }
+}

src/Explorer.Storage.Sqlite/SqliteIndexStore.cs

@@ -13,6 +13,7 @@ public sealed class SqliteIndexStore : IIndexStore, IAsyncDisposable
     private readonly SemaphoreSlim _writeLock = new(1, 1);
     private readonly AsyncLocal<int> _writeDepth = new();
     private SqliteConnection? _write;
+    private IndexStoreLock? _lock;
     private bool _opened;
     private int _analysisIndexesReady;
 
@@ -58,6 +59,9 @@ public sealed class SqliteIndexStore : IIndexStore, IAsyncDisposable
             return;
         }
 
+        _lock = IndexStoreLock.Acquire(_path);
+        try
+        {
             DapperSetup.Ensure();
             Directory.CreateDirectory(Path.GetDirectoryName(_path)!);
             _write = new SqliteConnection(BuildConnectionString(_path));
@@ -72,8 +76,17 @@ public sealed class SqliteIndexStore : IIndexStore, IAsyncDisposable
             _opened = true;
             _logger.LogInformation("Opened index database at {Path}", _path);
         }
+        catch
+        {
+            _lock.Dispose();
+            _lock = null;
+            throw;
+        }
+    }
 
     public async Task CloseAsync()
+    {
+        try
         {
             if (_write is not null)
             {
@@ -81,8 +94,13 @@ public sealed class SqliteIndexStore : IIndexStore, IAsyncDisposable
                 await _write.DisposeAsync().ConfigureAwait(false);
                 _write = null;
             }
-
+        }
+        finally
+        {
             _opened = false;
+            _lock?.Dispose();
+            _lock = null;
+        }
     }
 
     public async Task<string> QuickCheckAsync(CancellationToken cancellationToken = default)

src/Explorer.Windows/WindowsElevatedScanService.cs

@@ -21,6 +21,7 @@ public sealed class WindowsElevatedScanService : IElevatedScanService
         }
     }
 
+    // Queue, index writer, and watchers stay in the user session. Elevation is never requested.
     public bool CanRequestElevation => false;
 
     public string ProtectedContentHint => "Protected content requires administrator privileges.";

tests/Explorer.Application.Tests/RemovableAutoIndexPlannerTests.cs

@@ -0,0 +1,73 @@
+using Explorer.Application;
+using Explorer.Domain;
+using Explorer.Windows;
+
+namespace Explorer.Application.Tests;
+
+public class RemovableAutoIndexPlannerTests
+{
+    [Fact]
+    public void Does_nothing_when_disabled()
+    {
+        var sources = new[] { Removable(1, indexed: false) };
+        Assert.Empty(RemovableAutoIndexPlanner.SourceIdsToScan(sources, autoIndexRemovable: false));
+    }
+
+    [Fact]
+    public void Queues_online_unindexed_removable_only()
+    {
+        var sources = new[]
+        {
+            Removable(1, indexed: false),
+            Removable(2, indexed: true),
+            Removable(3, indexed: false, status: SourceStatus.Offline),
+            Cloud(4),
+            Local(5)
+        };
+        Assert.Equal(new[] { 1L }, RemovableAutoIndexPlanner.SourceIdsToScan(sources, autoIndexRemovable: true));
+    }
+
+    private static Source Removable(long id, bool indexed, SourceStatus status = SourceStatus.Online)
+        => new()
+        {
+            Id = id,
+            StableKey = id.ToString(),
+            Kind = SourceKind.Removable,
+            DisplayName = "USB",
+            LastRootPath = @"E:\",
+            Status = status,
+            LastIndexedUtc = indexed ? DateTimeOffset.UtcNow : null
+        };
+
+    private static Source Cloud(long id)
+        => new()
+        {
+            Id = id,
+            StableKey = "cloud",
+            Kind = SourceKind.Cloud,
+            DisplayName = "Cloud",
+            LastRootPath = @"C:\Users\me\OneDrive",
+            Status = SourceStatus.Online
+        };
+
+    private static Source Local(long id)
+        => new()
+        {
+            Id = id,
+            StableKey = "local",
+            Kind = SourceKind.NtfsLocal,
+            DisplayName = "Local",
+            LastRootPath = @"C:\",
+            Status = SourceStatus.Online
+        };
+}
+
+public class ElevatedScanServiceTests
+{
+    [Fact]
+    public void Never_requests_elevation()
+    {
+        IElevatedScanService service = new WindowsElevatedScanService();
+        Assert.False(service.CanRequestElevation);
+    }
+}

tests/Explorer.Application.Tests/UiPreferencesStoreTests.cs

@@ -43,6 +43,18 @@ public class UiPreferencesStoreTests
         Assert.Equal(@"C:\Program Files\Git\cmd\git.exe", prefs.GitPath);
     }
 
+    [Fact]
+    public void Parse_reads_host_and_removable_index_flags()
+    {
+        var prefs = UiPreferencesStore.Parse(
+        [
+            "auto-index-removable=true",
+            "background-host-at-logon=true"
+        ]);
+        Assert.True(prefs.AutoIndexRemovable);
+        Assert.True(prefs.BackgroundHostAtLogon);
+    }
+
     [Fact]
     public void Parse_defaults_missing_keys()
     {
@@ -54,6 +66,8 @@ public class UiPreferencesStoreTests
         Assert.True(prefs.ShowHiddenFiles);
         Assert.False(prefs.ShowProtectedSystemLocations);
         Assert.False(prefs.AutoClearQueueWhenDone);
+        Assert.False(prefs.AutoIndexRemovable);
+        Assert.False(prefs.BackgroundHostAtLogon);
         Assert.Null(prefs.SevenZipPath);
         Assert.Null(prefs.GitPath);
     }
@@ -95,6 +109,8 @@ public class UiPreferencesStoreTests
             Assert.True(loaded.ShowHiddenFiles);
             Assert.False(loaded.ShowProtectedSystemLocations);
             Assert.True(loaded.AutoClearQueueWhenDone);
+            Assert.False(loaded.AutoIndexRemovable);
+            Assert.False(loaded.BackgroundHostAtLogon);
             Assert.Equal(1100, loaded.WindowWidth);
             Assert.Equal(720, loaded.WindowHeight);
             Assert.Equal(300, loaded.TreeWidth);

tests/Explorer.Application.Tests/WorkbenchHostTests.cs

@@ -0,0 +1,60 @@
+using Explorer.Application;
+using Explorer.Contracts;
+using Explorer.Domain;
+
+namespace Explorer.Application.Tests;
+
+public class WorkbenchHostTests
+{
+    [Fact]
+    public void Forwards_indexing_and_transfer_sessions()
+    {
+        var indexing = new FakeIndexing();
+        var transfers = new FakeTransfers();
+        IWorkbenchHost host = new WorkbenchHost(indexing, transfers);
+        Assert.Same(indexing, host.Indexing);
+        Assert.Same(transfers, host.Transfers);
+
+        host.Indexing.EnqueueFullScan(7);
+        host.Transfers.PauseAll();
+        Assert.Equal(7, indexing.FullScanId);
+        Assert.True(transfers.PausedAll);
+    }
+
+    private sealed class FakeIndexing : IIndexingHost
+    {
+        public long FullScanId { get; private set; }
+        public event EventHandler<ScanProgress>? ProgressChanged;
+
+        public void EnqueueFullScan(long sourceId) => FullScanId = sourceId;
+        public void EnqueueFolderScan(long sourceId, string pathRel) { }
+        public void EnqueueReconcile(long sourceId, string pathRel) { }
+        public void Cancel(long sourceId) { }
+
+        public void Raise() => ProgressChanged?.Invoke(this, new ScanProgress
+        {
+            SourceId = 1,
+            CurrentPath = "",
+            Status = ScanJobStatus.Running
+        });
+    }
+
+    private sealed class FakeTransfers : ITransferHost
+    {
+        public bool PausedAll { get; private set; }
+        public event EventHandler? Changed = delegate { };
+        public event EventHandler<TransferJob>? JobFinished = delegate { };
+        public bool IsPaused => PausedAll;
+        public IReadOnlyList<TransferJob> Snapshot() => [];
+        public void PauseAll() => PausedAll = true;
+        public void ResumeAll() => PausedAll = false;
+        public void Pause(long jobId) { }
+        public void Resume(long jobId) { }
+        public void Retry(long jobId) { }
+        public void Cancel(long jobId) { }
+        public void Dismiss(long jobId) { }
+        public void ClearFinished() { }
+        public bool MoveUp(long jobId) => false;
+        public bool MoveDown(long jobId) => false;
+    }
+}

tests/Explorer.Hosting.Tests/CoreRegistrationTests.cs

@@ -0,0 +1,48 @@
+using Explorer.Contracts;
+using Explorer.Domain;
+using Explorer.Domain.Abstractions;
+using Explorer.Hosting;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Explorer.Hosting.Tests;
+
+public class CoreRegistrationTests
+{
+    [Fact]
+    public async Task AddExplorerCore_registers_workbench_without_clipboard()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "ew-hosting", Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(dir);
+        try
+        {
+            var services = new ServiceCollection();
+            services.AddLogging();
+            services.AddSingleton<IAppEnvironment>(new TempEnv(dir));
+            services.AddExplorerCore();
+            await using var sp = services.BuildServiceProvider();
+            Assert.NotNull(sp.GetService<IWorkbenchHost>());
+            Assert.NotNull(sp.GetService<IIndexingHost>());
+            Assert.NotNull(sp.GetService<ITransferHost>());
+            Assert.Null(sp.GetService<IOsClipboard>());
+        }
+        finally
+        {
+            try { Directory.Delete(dir, true); } catch { /* ignore */ }
+        }
+    }
+
+    private sealed class TempEnv : IAppEnvironment
+    {
+        public TempEnv(string dir)
+        {
+            DataDirectory = dir;
+            DatabasePath = Path.Combine(dir, "index.db");
+            LogDirectory = Path.Combine(dir, "logs");
+            Directory.CreateDirectory(LogDirectory);
+        }
+
+        public string DataDirectory { get; }
+        public string DatabasePath { get; }
+        public string LogDirectory { get; }
+    }
+}

tests/Explorer.Hosting.Tests/Explorer.Hosting.Tests.csproj

@@ -0,0 +1,22 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="10.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="10.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Explorer.Application\Explorer.Application.csproj" />
+    <ProjectReference Include="..\..\src\Explorer.Contracts\Explorer.Contracts.csproj" />
+    <ProjectReference Include="..\..\src\Explorer.Domain\Explorer.Domain.csproj" />
+    <ProjectReference Include="..\..\src\Explorer.Hosting\Explorer.Hosting.csproj" />
+  </ItemGroup>
+</Project>

tests/Explorer.Hosting.Tests/HostLogonAutostartTests.cs

@@ -0,0 +1,19 @@
+using Explorer.Hosting;
+
+namespace Explorer.Hosting.Tests;
+
+public class HostLogonAutostartTests
+{
+    [Fact]
+    public void Create_args_are_per_user_logon_not_system_service()
+    {
+        var args = HostLogonAutostart.CreateTaskArgs(@"C:\Tools\Explorer.Host.exe");
+        Assert.Contains("/SC", args);
+        Assert.Contains("ONLOGON", args);
+        Assert.Contains("/RL", args);
+        Assert.Contains("LIMITED", args);
+        Assert.Contains(HostLogonAutostart.TaskName, args);
+        Assert.DoesNotContain("ONSTART", args);
+        Assert.DoesNotContain("/RU", args);
+    }
+}

tests/Explorer.Hosting.Tests/WorkbenchPipeTests.cs

@@ -0,0 +1,76 @@
+using Explorer.Application;
+using Explorer.Contracts;
+using Explorer.Domain;
+using Explorer.Hosting.Ipc;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace Explorer.Hosting.Tests;
+
+public class WorkbenchPipeTests
+{
+    [Fact]
+    public void Handle_forwards_indexing_and_transfer_calls()
+    {
+        var indexing = new FakeIndexing();
+        var transfers = new FakeTransfers();
+        var server = new WorkbenchPipeServer(
+            new WorkbenchHost(indexing, transfers),
+            new WorkbenchIpcOptions { PipeName = "ew-test" },
+            NullLogger<WorkbenchPipeServer>.Instance);
+
+        var ping = server.Handle(new IpcEnvelope { V = WorkbenchIpc.ProtocolVersion, Op = "Ping" });
+        Assert.True(ping.Ok);
+
+        var scan = server.Handle(new IpcEnvelope { V = WorkbenchIpc.ProtocolVersion, Op = "Indexing.EnqueueFullScan", N = 42 });
+        Assert.True(scan.Ok);
+        Assert.Equal(42, indexing.FullScanId);
+
+        var pause = server.Handle(new IpcEnvelope { V = WorkbenchIpc.ProtocolVersion, Op = "Transfers.PauseAll" });
+        Assert.True(pause.Ok);
+        Assert.True(transfers.PausedAll);
+
+        var paused = server.Handle(new IpcEnvelope { V = WorkbenchIpc.ProtocolVersion, Op = "Transfers.IsPaused" });
+        Assert.True(paused.Paused);
+    }
+
+    [Fact]
+    public void Handle_rejects_other_protocol_versions()
+    {
+        var server = new WorkbenchPipeServer(
+            new WorkbenchHost(new FakeIndexing(), new FakeTransfers()),
+            new WorkbenchIpcOptions(),
+            NullLogger<WorkbenchPipeServer>.Instance);
+        var reply = server.Handle(new IpcEnvelope { V = 99, Op = "Ping" });
+        Assert.False(reply.Ok);
+        Assert.Contains("99", reply.Error);
+    }
+
+    private sealed class FakeIndexing : IIndexingHost
+    {
+        public long FullScanId { get; private set; }
+        public event EventHandler<ScanProgress>? ProgressChanged = delegate { };
+        public void EnqueueFullScan(long sourceId) => FullScanId = sourceId;
+        public void EnqueueFolderScan(long sourceId, string pathRel) { }
+        public void EnqueueReconcile(long sourceId, string pathRel) { }
+        public void Cancel(long sourceId) { }
+    }
+
+    private sealed class FakeTransfers : ITransferHost
+    {
+        public bool PausedAll { get; private set; }
+        public event EventHandler? Changed = delegate { };
+        public event EventHandler<TransferJob>? JobFinished = delegate { };
+        public bool IsPaused => PausedAll;
+        public IReadOnlyList<TransferJob> Snapshot() => [];
+        public void PauseAll() => PausedAll = true;
+        public void ResumeAll() => PausedAll = false;
+        public void Pause(long jobId) { }
+        public void Resume(long jobId) { }
+        public void Retry(long jobId) { }
+        public void Cancel(long jobId) { }
+        public void Dismiss(long jobId) { }
+        public void ClearFinished() { }
+        public bool MoveUp(long jobId) => false;
+        public bool MoveDown(long jobId) => false;
+    }
+}

tests/Explorer.Storage.Tests/StorageTests.cs

@@ -427,3 +427,28 @@ public class FileRelationTests
         Assert.Empty(await store.OperationProfiles.ListAsync());
     }
 }
+
+public class IndexStoreLockTests
+{
+    [Fact]
+    public async Task Second_writer_on_same_path_is_rejected()
+    {
+        var path = Path.Combine(Path.GetTempPath(), "ew-tests", Guid.NewGuid().ToString("N"), "index.db");
+        await using var first = new SqliteIndexStore(path, NullLogger<SqliteIndexStore>.Instance);
+        await first.OpenAsync();
+        var second = new SqliteIndexStore(path, NullLogger<SqliteIndexStore>.Instance);
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => second.OpenAsync());
+        Assert.Contains("already in use", ex.Message, StringComparison.OrdinalIgnoreCase);
+        await first.DisposeAsync();
+        await second.OpenAsync();
+        await second.DisposeAsync();
+    }
+
+    [Fact]
+    public void Mutex_name_is_stable_for_the_same_path()
+    {
+        var path = @"C:\Users\me\AppData\Local\ExplorerWorkbench\index.db";
+        Assert.Equal(IndexStoreLock.MutexNameFor(path), IndexStoreLock.MutexNameFor(path));
+        Assert.StartsWith(@"Local\ExplorerWorkbench-Index-", IndexStoreLock.MutexNameFor(path));
+    }
+}