diff --git a/ILSpy.Tests/Input/HeadlessMmbPointerTests.cs b/ILSpy.Tests/Input/HeadlessMmbPointerTests.cs
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+++ b/ILSpy.Tests/Input/HeadlessMmbPointerTests.cs
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+// Copyright (c) 2026 AlphaSierraPapa for the SharpDevelop Team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System.Linq;
+using System.Threading.Tasks;
+
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.DataGridHierarchical;
+using Avalonia.Headless;
+using Avalonia.Headless.NUnit;
+using Avalonia.Input;
+using Avalonia.VisualTree;
+
+using AwesomeAssertions;
+
+using ILSpy.AppEnv;
+using ILSpy.AssemblyTree;
+using ILSpy.Docking;
+using ILSpy.TreeNodes;
+using ILSpy.ViewModels;
+using ILSpy.Views;
+
+using NUnit.Framework;
+
+namespace ICSharpCode.ILSpy.Tests.Input;
+
+/// <summary>
+/// Drives a real <see cref="HeadlessWindowExtensions.MouseDown"/> event through the
+/// input pipeline so the MMB → "open in new tab" gesture is verified end-to-end
+/// rather than via a synthetic <c>OpenNodeInNewTab</c> call. Catches routing regressions
+/// (the existing synthetic tests would pass even if the PointerPressed handler stopped
+/// being installed).
+/// </summary>
+[TestFixture]
+public class HeadlessMmbPointerTests
+{
+	[AvaloniaTest]
+	public async Task Middle_Click_On_An_Assembly_Tree_Row_Opens_A_New_Decompiler_Tab()
+	{
+		// Boot + load enough assemblies that we have visible rows.
+		var window = AppComposition.Current.GetExport<MainWindow>();
+		window.Show();
+		var vm = (MainWindowViewModel)window.DataContext!;
+		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 1);
+
+		var pane = await window.WaitForComponent<AssemblyListPane>();
+		var grid = await pane.WaitForComponent<DataGrid>();
+
+		// Any realised DataGridRow whose DataContext wraps an ILSpyTreeNode is a valid click
+		// target — the exact node doesn't matter, only that the gesture pipeline fires.
+		// ProDataGrid wraps each row's data in a HierarchicalNode (`{ Item: ILSpyTreeNode }`),
+		// so we walk that surface rather than comparing against the tree node directly.
+		await Waiters.WaitForAsync(() => grid.GetVisualDescendants().OfType<DataGridRow>()
+			.Any(r => r.DataContext is HierarchicalNode { Item: ILSpyTreeNode }));
+		var row = grid.GetVisualDescendants().OfType<DataGridRow>()
+			.First(r => r.DataContext is HierarchicalNode { Item: ILSpyTreeNode });
+
+		// Snapshot the tab count BEFORE the gesture so we can assert a strict +1 after.
+		var documents = ((ILSpyDockFactory)vm.DockWorkspace.Factory).Documents!;
+		int before = documents.VisibleDockables?.Count ?? 0;
+
+		// Translate the row's centre into TopLevel coordinates so MouseDown lands inside it.
+		var topLevel = TopLevel.GetTopLevel(row)!;
+		var rowBounds = row.Bounds;
+		var centreInRow = new Point(rowBounds.Width / 2, rowBounds.Height / 2);
+		var centreInTopLevel = row.TranslatePoint(centreInRow, topLevel)
+			?? throw new System.InvalidOperationException("Row not in TopLevel visual tree");
+
+		// Real pointer event — exercises bubble + handledEventsToo routing through ProDataGrid.
+		topLevel.MouseDown(centreInTopLevel, MouseButton.Middle);
+		topLevel.MouseUp(centreInTopLevel, MouseButton.Middle);
+
+		// Wait for the tab to land. Without WaitForAsync this races the async decompile path.
+		await Waiters.WaitForAsync(() => (documents.VisibleDockables?.Count ?? 0) > before);
+
+		(documents.VisibleDockables?.Count ?? 0).Should().Be(before + 1);
+	}
+}