feat: place caret inside inserted function parentheses\n\n- Add CaretIndex to MainViewModel and bind TextBox.CaretIndex\n- After function insertion, set caret to inside parentheses\n- Return focus to input box for immediate typing

src/AdvancedCalculator/ViewModels/MainViewModel.cs

@@ -35,6 +35,10 @@ public partial class MainViewModel : ViewModelBase
     [ObservableProperty]
     private int _selectedHistoryIndex = -1;
 
+    // Caret position in the input TextBox
+    [ObservableProperty]
+    private int _caretIndex;
+
     public ObservableCollection<HistoryItem> History { get; }
     public ObservableCollection<VariableItem> Variables { get; }
 
@@ -61,6 +65,11 @@ public partial class MainViewModel : ViewModelBase
         if (string.IsNullOrWhiteSpace(functionDefintionItem.FunctionName))
             return;
         InsertToken(functionDefintionItem.FunctionName + "()");
+        // Place caret inside the parentheses
+        if (!string.IsNullOrEmpty(InputText))
+        {
+            CaretIndex = Math.Max(0, InputText.Length - 1);
+        }
         // Close the functions flyout after insertion for smoother UX
         IsFunctionsPanelOpen = false;
     }

src/AdvancedCalculator/Views/MainView.axaml

@@ -136,9 +136,7 @@
             <Button.Flyout>
                 <Flyout 
                         IsOpen="{Binding IsFunctionsPanelOpen, Mode=TwoWay}"
-                        Placement="BottomEdgeAlignedLeft"
-                        Opened="OnFunctionsFlyoutOpened"
-                        Closed="OnFunctionsFlyoutClosed">
+                        Placement="BottomEdgeAlignedLeft">
                     <Border x:Name="FunctionsPanelRoot" Padding="8" MinWidth="360" MaxHeight="420"
                             Background="{DynamicResource Brush.Surface}" BorderBrush="{DynamicResource Brush.Border}" BorderThickness="1" CornerRadius="6">
                         <ScrollViewer>
@@ -162,7 +160,7 @@
                                                         <DataTemplate x:DataType="m:FunctionDefinitionItem">
                                                             <Border Background="Transparent" Padding="8" MinHeight="36"
                                                                     AutomationProperties.Name="Insert function"
-																	Tapped="OnFunctionsItemTapped">
+                                                                    Tapped="OnFunctionsItemTapped">
                                                                 <Grid ColumnDefinitions="*,Auto">
                                                                     <StackPanel>
                                                                         <TextBlock Text="{Binding FunctionName}" FontWeight="Bold"/>
@@ -185,7 +183,9 @@
             <TextBlock FontFamily="{StaticResource MDI}" Text="{x:Static m:IconFont.Function}" />
         </Button>
 
-                    <TextBox Grid.Column="2" Text="{Binding InputText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" MinHeight="44"
+                    <TextBox x:Name="InputBox" Grid.Column="2" Text="{Binding InputText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
+                             CaretIndex="{Binding CaretIndex, Mode=TwoWay}"
+                             MinHeight="44"
                              AutomationProperties.Name="Expression input"
                              Watermark="Type an expression (e.g., 2 + 2)">
                         <InputElement.KeyBindings>

src/AdvancedCalculator/Views/MainView.axaml.cs

@@ -21,7 +21,7 @@ public partial class MainView : UserControl
 
     private MainViewModel? _vm;
     private ListBox? _historyList;
-    private Border? _functionsPanelRoot;
+    // Functions flyout is handled via per-item Tapped in XAML
 
     private void OnAttachedToVisualTree(object? sender, VisualTreeAttachmentEventArgs e)
     {
@@ -53,12 +53,6 @@ public partial class MainView : UserControl
             _historyList.RemoveHandler(InputElement.TappedEvent, OnHistoryTapped);
             _historyList = null;
         }
-        // Detach functions panel tap handler if still attached
-        if (_functionsPanelRoot is not null)
-        {
-            _functionsPanelRoot.RemoveHandler(InputElement.TappedEvent, OnFunctionsItemTapped);
-            _functionsPanelRoot = null;
-        }
         _vm = null;
     }
 
@@ -100,27 +94,12 @@ public partial class MainView : UserControl
             _vm?.InsertFunctionCommand.CanExecute(item) == true)
         {
             _vm.InsertFunctionCommand.Execute(item);
+            // Return focus to the input box so the caret is active
+            var input = this.FindControl<TextBox>("InputBox");
+            input?.Focus();
             e.Handled = true;
         }
     }
 
-
-    private void OnFunctionsFlyoutOpened(object? sender, EventArgs e)
-{
-    if (sender is Flyout flyout && sender is ContentPresenter presenter)
-    {
-        _functionsPanelRoot = presenter.FindControl<Border>("FunctionsPanelRoot");
-        _functionsPanelRoot?.AddHandler(InputElement.TappedEvent, OnFunctionsItemTapped,
-            RoutingStrategies.Tunnel | RoutingStrategies.Bubble);
-    }
-}
-
-    private void OnFunctionsFlyoutClosed(object? sender, EventArgs e)
-    {
-        if (_functionsPanelRoot is not null)
-        {
-            _functionsPanelRoot.RemoveHandler(InputElement.TappedEvent, OnFunctionsItemTapped);
-            _functionsPanelRoot = null;
-        }
-    }
+    // Removed Opened/Closed dynamic wiring; handled directly in XAML.
 }