Freeze the preview tab when it is floated out into its own window

MoveDockable freezes the One on in-strip and cross-dock drags, but the tear-off-to-floating-window gesture never reaches it: Dock funnels that through CreateWindowFrom (FloatDockable -> SplitToWindow -> CreateWindowFrom), where the torn-off document is still the One before it gets wrapped in a fresh dock. Overriding it makes a float-out one more way to keep the tab, consistent with every other drag.

ILSpy.Tests/Docking/PreviewTabPromotionTests.cs

@@ -727,6 +727,31 @@ public class PreviewTabPromotionTests
 			"freeze-on-drag does not rotate MainTab; the next tree selection forges a fresh One");
 	}
 
+	[AvaloniaTest]
+	public async Task Floating_The_Preview_Out_Freezes_It()
+	{
+		// Tearing the One out into its own floating window does NOT go through MoveDockable -- the
+		// drag-to-float gesture funnels through CreateWindowFrom (FloatDockable -> SplitToWindow ->
+		// CreateWindowFrom). That override must freeze the One just like an in-strip drag. Drive
+		// CreateWindowFrom directly (what the float gesture ultimately calls).
+		var (_, vm) = await TestHarness.BootAsync(3);
+		var factory = (ILSpyDockFactory)vm.DockWorkspace.Factory;
+
+		var typeA = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Linq", "System.Linq", "System.Linq.Enumerable");
+		vm.AssemblyTreeModel.SelectNode(typeA);
+		vm.DockWorkspace.SettleSelection();
+		var theOne = factory.MainTab!;
+		theOne.IsPreview.Should().BeTrue("precondition: the One starts as the preview");
+
+		factory.CreateWindowFrom(theOne);
+
+		theOne.IsPreview.Should().BeFalse(
+			"floating the One out must freeze it -- it becomes an ordinary, movable tab");
+		factory.MainTab.Should().BeSameAs(theOne,
+			"float-out does not rotate MainTab; the next tree selection forges a fresh One");
+	}
+
 	[AvaloniaTest]
 	public async Task Frozen_Tab_Cannot_Be_Reordered_Before_The_Preview()
 	{

ILSpy/Docking/ILSpyDockFactory.cs

@@ -122,6 +122,17 @@ namespace ILSpy.Docking
 			base.MoveDockable(sourceDock, targetDock, sourceDockable, targetDockable);
 		}
 
+		// Tearing the One out into its own floating window doesn't go through MoveDockable -- the
+		// drag-to-float gesture funnels through CreateWindowFrom (FloatDockable -> SplitToWindow ->
+		// CreateWindowFrom), with the torn-off document passed straight through before it's wrapped
+		// in a fresh dock. Freeze the One here too so a float-out is just another way to keep it.
+		public override IDockWindow? CreateWindowFrom(IDockable dockable)
+		{
+			if (ReferenceEquals(dockable, MainTab) && MainTab is { IsPreview: true })
+				FreezeCurrentMainTab();
+			return base.CreateWindowFrom(dockable);
+		}
+
 		// Self-healing insurance: re-assert the One at index 0 after any drag -- but ONLY while it is
 		// still the preview. Once dragged (which freezes it) it's an ordinary tab and must stay where
 		// the user dropped it. Idempotent; guards against a future Dock version routing a reorder