Fix: Dropdown menu overlayed in Inference UI Model Cards not being scrollable on Linux.

StabilityMatrix.Avalonia/Controls/FADownloadableComboBox.cs

@@ -2,12 +2,17 @@
 using System.Threading.Tasks;
 using AsyncAwaitBestPractices;
 using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.VisualTree;
 using CommunityToolkit.Mvvm.Input;
 using FluentAvalonia.UI.Controls;
 using Microsoft.Extensions.DependencyInjection;
 using StabilityMatrix.Avalonia.Services;
 using StabilityMatrix.Avalonia.ViewModels.Base;
 using StabilityMatrix.Avalonia.ViewModels.Dialogs;
+using StabilityMatrix.Core.Helper;
 using StabilityMatrix.Core.Models;
 
 namespace StabilityMatrix.Avalonia.Controls;
@@ -17,6 +22,66 @@ public partial class FADownloadableComboBox : FAComboBox
 {
     protected override Type StyleKeyOverride => typeof(FAComboBox);
 
+    private Popup? dropDownPopup;
+    private IDisposable? openSubscription;
+
+    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+    {
+        base.OnApplyTemplate(e);
+
+        CleanupSubscription();
+        DropDownOpened -= OnDropDownOpenedHandler;
+        DropDownClosed -= OnDropDownClosedHandler;
+
+        // Template part name is "Popup" per FAComboBox.properties.cs (s_tpPopup = "Popup")
+        dropDownPopup = e.NameScope.Find<Popup>("Popup");
+
+        DropDownOpened += OnDropDownOpenedHandler;
+        DropDownClosed += OnDropDownClosedHandler;
+    }
+
+    private void OnDropDownOpenedHandler(object? sender, EventArgs e)
+    {
+        CleanupSubscription();
+
+        if (dropDownPopup?.Child is not Control popupChild)
+            return;
+
+        var scrollViewer = popupChild.GetVisualDescendants().OfType<ScrollViewer>().FirstOrDefault();
+
+        if (scrollViewer == null)
+            return;
+
+        // On Unix-like systems, overlay popups share the same TopLevel visual root as the main window.
+        // FAComboBox.OnPopupOpened adds a TopLevel tunnel handler that marks all wheel eventsas handled while the dropdown is open,
+        // which inadvertently blocks scroll-wheelevents in popup menus in Inference model cards.
+        // Resetting e.Handled on the ScrollViewer's tunnel phase counters this.
+        if (!Compat.IsUnix)
+            return;
+
+        openSubscription = scrollViewer.AddDisposableHandler(
+            PointerWheelChangedEvent,
+            static (_, ev) =>
+            {
+                if (ev.Handled)
+                    ev.Handled = false;
+            },
+            RoutingStrategies.Tunnel,
+            handledEventsToo: true
+        );
+    }
+
+    private void OnDropDownClosedHandler(object? sender, EventArgs e)
+    {
+        CleanupSubscription();
+    }
+
+    private void CleanupSubscription()
+    {
+        openSubscription?.Dispose();
+        openSubscription = null;
+    }
+
     static FADownloadableComboBox()
     {
         SelectionChangedEvent.AddClassHandler<FADownloadableComboBox>(