Fix startup binding errors and background load sweep failure

[christophwille]

The console of a "Start Debugging" session in VS Code showed 12 [Binding] errors in three groups and one swallowed exception. Each has its own commit; this is what was in the output and how it was fixed.

1. Update banner (6 errors)

[Binding]An error occurred binding 'IsVisible' to 'IsPanelVisible' at 'IsPanelVisible': 'Unable to cast object of type 'ICSharpCode.ILSpy.ViewModels.MainWindowViewModel' to type 'ICSharpCode.ILSpy.ViewModels.UpdatePanelViewModel'.' (UpdatePanel #19766715)

The same error was logged for UpdateAvailable, Message, ButtonText, DownloadOrCheckUpdateCommand and CloseCommand.

• Cause: MainWindow.axaml gave the panel a DataContext="{Binding UpdatePanel}" of its own. Until that binding produced a value the panel inherited the window's MainWindowViewModel, and its compiled bindings (x:DataType="vm:UpdatePanelViewModel") failed the cast.
• Fix: the panel is hosted in a ContentControl with a DataTemplate, so it never sees the window's view model.

2. Dock chrome (4 errors)

[Binding]An error occurred binding '(unknown)' to 'DockCapabilityOverrides.CanDrag' at 'DockCapabilityOverrides': 'Value is null.' (ToolChromeControl #61244865)

Logged for CanDrag and CanDrop, on both ToolChromeControl and DocumentControl.

• Cause: the Dock theme (checked by decompiling Dock.Avalonia.Themes.Simple 12.1.0.6) binds DockCapabilityOverrides.CanDrag/CanDrop on the tool and document docks themselves. ILSpyDockFactory only set that property on panes and tabs, and a layout restored from disk bypasses CreateLayout altogether.
• Fix: InitLayout fills in DockCapabilityOverrides for every dockable, which covers fresh and restored layouts. The tool dock created on demand after InitLayout gets it in its initializer.

3. Tree connector lines (2 errors)

[Binding]An error occurred binding 'IsVisible' to '$visualParent[SharpTreeView].ShowLines' at '$visualParent[SharpTreeView]': 'Ancestor not found.' (TreeLines #35340021)

• Cause: the row template bound TreeLines.IsVisible to ShowLines on a SharpTreeView ancestor, and the binding was evaluated while the row content was not under one. The exact moment was not reproduced in the headless tests.
• Fix: the binding is removed. ShowLines is now an inherited property that TreeLines reads directly, so there is no ancestor lookup left to fail. The DataGridHierarchicalPresenter use of TreeLines has no SharpTreeView above it and keeps the default (lines shown).

4. Background load sweep

[AssemblyTreeModel] background load sweep failed: System.IO.DirectoryNotFoundException: Could not find a part of the path '.../sdk/11.0.100-preview.6.26359.118/Roslyn/Microsoft.Build.Tasks.CodeAnalysis.dll'.

• Cause: one assembly-list entry that could not be loaded faulted the whole sweep, which skipped the CommandManager.InvalidateRequerySuggested() at its end. "Remove assemblies with load errors" was therefore not re-evaluated in the one case it exists for.
• Fix: the per-assembly task catches the load failure (it is already recorded on the LoadedAssembly as HasLoadError), so the sweep always reaches the requery.

Tests

• StartupBindingErrorTests boots the main window with a capturing Avalonia log sink and fails on any binding error. It was red for group 1 and, separately, for group 2 before the fixes.
• BackgroundLoadSweepTests shows a list whose only assembly fails to load at a moment the test controls, and waits for the requery. It timed out before the fix. AssemblyTreeModel.ShowAssemblyList(AssemblyList) went from private to internal for it.
• SharpTreeViewTests gained a case that rows follow the tree view's ShowLines. It does not reproduce the original "Ancestor not found" error.
• Full ILSpy.Tests run: 1315 succeeded, 3 skipped, 0 failed.

Not verified: a fresh "Start Debugging" session in VS Code to confirm the console is clean.

Assisted-by: Claude:claude-fable-5-1:Claude Code