Stop console auto-scroll from fighting manual scroll-up

src/UniGetUI.Avalonia/Views/Controls/LogTextEditor.cs

@@ -81,6 +81,9 @@ public void ClearLines()
 
     public void ScrollToBottom() => ScrollToEnd();
 
+    // True when the view is pinned to the last line; used to keep auto-scroll from fighting a manual scroll-up.
+    public bool IsScrolledToBottom => ExtentHeight - ViewportHeight - VerticalOffset <= 1.0;
+
     // AvaloniaEdit auto-links URLs; its default link brush is too dark to read on the dark theme.
     private void UpdateLinkColor()
     {

src/UniGetUI.Avalonia/Views/DialogPages/OperationOutputWindow.axaml.cs

@@ -24,6 +24,7 @@ private void OnOutputLinesChanged(object? sender, NotifyCollectionChangedEventAr
     {
         Dispatcher.UIThread.Post(() =>
         {
+            bool wasAtBottom = OutputText.IsScrolledToBottom;
             if (e.Action == NotifyCollectionChangedAction.Reset)
             {
                 OutputText.ClearLines();
@@ -33,7 +34,9 @@ private void OnOutputLinesChanged(object? sender, NotifyCollectionChangedEventAr
                 foreach (LogLineItem item in e.NewItems)
                     OutputText.AppendLine(item);
             }
-            OutputText.ScrollToBottom();
+            // Only follow new output if the user hadn't scrolled up to read earlier lines.
+            if (wasAtBottom)
+                OutputText.ScrollToBottom();
         }, DispatcherPriority.Background);
     }