Assembly list switching in toolbar

- Hold AssemblyListManager on AssemblyTreeModel and mirror its
  AssemblyLists collection so the toolbar combo can bind to it.
- New ActiveListName ([ObservableProperty]); OnActiveListNameChanged
  loads the named list via the manager and rebuilds Root.
- The "seed initial assemblies if empty" fallback now only triggers
  for the (Default) list, so switching to an empty user list doesn't
  auto-populate it.
- MainToolBar AssemblyListComboBox bound to AssemblyLists /
  ActiveListName (TwoWay).

Assisted-by: Claude:claude-opus-4-7:Claude Code

ILSpy.Tests/AssemblyTree/AssemblyTreeModelTests.cs

@@ -20,6 +20,8 @@ using Avalonia.Headless.NUnit;
 
 using AwesomeAssertions;
 
+using ICSharpCode.ILSpyX;
+
 using ILSpy.AppEnv;
 using ILSpy.AssemblyTree;
 
@@ -46,4 +48,16 @@ public class AssemblyTreeModelTests
 		model.AssemblyList.Should().NotBeNull("Initialize loads or creates the default AssemblyList.");
 		model.Root.Should().NotBeNull("Initialize wires Root to an AssemblyListTreeNode of the loaded list.");
 	}
+
+	[AvaloniaTest]
+	public void Initialize_populates_AssemblyLists_and_selects_the_default()
+	{
+		var model = AppComposition.Current.GetExport<AssemblyTreeModel>();
+		model.Initialize();
+
+		model.AssemblyLists.Should().NotBeEmpty(
+			"Initialize mirrors AssemblyListManager.AssemblyLists into the toolbar combo's source.");
+		model.ActiveListName.Should().Be(AssemblyListManager.DefaultListName,
+			"Initialize selects the (Default) list so the tree has something to render at startup.");
+	}
 }

ILSpy/AssemblyTree/AssemblyTreeModel.cs

@@ -17,6 +17,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Collections.ObjectModel;
 using System.Composition;
 using System.Runtime.Serialization;
 
@@ -37,6 +38,8 @@ namespace ILSpy.AssemblyTree
 	{
 		public const string PaneContentId = "AssemblyTree";
 
+		AssemblyListManager? listManager;
+
 		[ObservableProperty]
 		[property: IgnoreDataMember]
 		private SharpTreeNode? root;
@@ -45,9 +48,16 @@ namespace ILSpy.AssemblyTree
 		[property: IgnoreDataMember]
 		private SharpTreeNode? selectedItem;
 
+		[ObservableProperty]
+		[property: IgnoreDataMember]
+		private string? activeListName;
+
 		[IgnoreDataMember]
 		public AssemblyList? AssemblyList { get; private set; }
 
+		[IgnoreDataMember]
+		public ObservableCollection<string> AssemblyLists { get; } = [];
+
 		public AssemblyTreeModel()
 		{
 			Id = PaneContentId;
@@ -58,12 +68,32 @@ namespace ILSpy.AssemblyTree
 		public void Initialize()
 		{
 			var settings = ILSpySettings.Load();
-			var listManager = new AssemblyListManager(settings);
+			listManager = new AssemblyListManager(settings);
 			listManager.CreateDefaultAssemblyLists();
 
-			AssemblyList = listManager.LoadList(AssemblyListManager.DefaultListName);
+			SyncListNames();
+			listManager.AssemblyLists.CollectionChanged += (_, _) => SyncListNames();
+
+			ActiveListName = AssemblyListManager.DefaultListName;
+		}
+
+		void SyncListNames()
+		{
+			if (listManager == null)
+				return;
+			AssemblyLists.Clear();
+			foreach (var name in listManager.AssemblyLists)
+				AssemblyLists.Add(name);
+		}
+
+		partial void OnActiveListNameChanged(string? value)
+		{
+			if (listManager == null || string.IsNullOrEmpty(value))
+				return;
+
+			AssemblyList = listManager.LoadList(value);
 
-			if (AssemblyList.GetAssemblies().Length == 0)
+			if (AssemblyList.GetAssemblies().Length == 0 && value == AssemblyListManager.DefaultListName)
 				LoadInitialAssemblies(AssemblyList);
 
 			var rootNode = new AssemblyListTreeNode(AssemblyList);

ILSpy/Views/MainToolBar.axaml

@@ -2,16 +2,19 @@
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:vm="using:ILSpy.ViewModels"
              mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="30"
-             x:Class="ILSpy.MainToolBar">
+             x:Class="ILSpy.MainToolBar"
+             x:DataType="vm:MainWindowViewModel">
 	<StackPanel Orientation="Horizontal" Height="30">
 		<!-- Navigation category (Back/Forward) inserted by MEF (task #10) -->
 		<Separator />
 		<!-- Open category inserted by MEF (task #10) -->
 		<Separator />
-		<!-- Assembly list combobox (task #6 / #11) -->
-		<ComboBox Name="AssemblyListComboBox" Margin="2,0"
-		          ToolTip.Tip="Select an assembly list" />
+		<ComboBox Name="AssemblyListComboBox" Margin="2,0" MinWidth="160"
+		          ToolTip.Tip="Select an assembly list"
+		          ItemsSource="{Binding AssemblyTreeModel.AssemblyLists}"
+		          SelectedItem="{Binding AssemblyTreeModel.ActiveListName, Mode=TwoWay}" />
 		<Separator />
 		<!-- Language selector (task #8) -->
 		<ComboBox Name="LanguageComboBox" Margin="2,0"