feat: add seating plan drag and quick assessment

LehrerApp.Desktop/Views/Groups/SeatAssessmentDialog.axaml

@@ -0,0 +1,133 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="clr-namespace:LehrerApp.Desktop.ViewModels.Groups"
+        x:Class="LehrerApp.Desktop.Views.Groups.SeatAssessmentDialog"
+        x:DataType="vm:SeatAssessmentViewModel"
+        Title="Sitzplatz-Schnelleingabe" Width="660" Height="700"
+        MinWidth="560" MinHeight="560" CanResize="True"
+        WindowStartupLocation="CenterOwner">
+  <Window.Styles>
+    <Style Selector="Button.choice">
+      <Setter Property="Background" Value="Transparent"/>
+      <Setter Property="BorderBrush" Value="{DynamicResource SystemControlForegroundBaseLowBrush}"/>
+      <Setter Property="BorderThickness" Value="1"/>
+      <Setter Property="Padding" Value="8,5"/>
+    </Style>
+    <Style Selector="Button.choice.selected">
+      <Setter Property="Background" Value="{DynamicResource SystemAccentColorLight2}"/>
+      <Setter Property="BorderBrush" Value="{DynamicResource SystemAccentColor}"/>
+      <Setter Property="BorderThickness" Value="2"/>
+    </Style>
+    <Style Selector="Border.aspectrow">
+      <Setter Property="BorderBrush" Value="Transparent"/>
+      <Setter Property="BorderThickness" Value="1"/>
+      <Setter Property="Background" Value="Transparent"/>
+    </Style>
+    <Style Selector="Border.aspectrow.active">
+      <Setter Property="BorderBrush" Value="{DynamicResource SystemAccentColor}"/>
+      <Setter Property="Background" Value="{DynamicResource SystemAccentColorLight3}"/>
+    </Style>
+  </Window.Styles>
+
+  <Grid RowDefinitions="Auto,*,Auto" Margin="20">
+    <Grid Grid.Row="0" ColumnDefinitions="*,Auto" Margin="0,0,0,14">
+      <StackPanel>
+        <TextBlock Text="{Binding StudentName}" FontSize="22" FontWeight="SemiBold"/>
+        <TextBlock Text="{Binding SessionDisplay}" FontSize="12" Opacity="0.55"/>
+      </StackPanel>
+      <Button Grid.Column="1" Content="Schließen" Click="OnClose" VerticalAlignment="Center"/>
+    </Grid>
+
+    <ScrollViewer Grid.Row="1">
+      <StackPanel Spacing="16" IsEnabled="{Binding CanEdit}">
+        <Border Background="#FFF3CD" CornerRadius="6" Padding="10"
+                IsVisible="{Binding CanEdit, Converter={x:Static BoolConverters.Not}}">
+          <TextBlock Text="{Binding ReadOnlyHint}" Foreground="#92400E" TextWrapping="Wrap"/>
+        </Border>
+
+        <StackPanel Spacing="7">
+          <TextBlock Text="MITARBEIT" FontSize="11" FontWeight="Bold" Opacity="0.5"/>
+          <ItemsControl ItemsSource="{Binding AspectRows}">
+            <ItemsControl.ItemTemplate>
+              <DataTemplate x:DataType="vm:SeatAssessmentAspectRow">
+                <Border Classes="aspectrow" Classes.active="{Binding IsActive}"
+                        CornerRadius="7" Padding="9" Margin="0,3">
+                  <Grid ColumnDefinitions="150,*">
+                    <StackPanel VerticalAlignment="Center">
+                      <TextBlock FontWeight="SemiBold">
+                        <Run Text="["/><Run Text="{Binding Shortcut}"/><Run Text="]  "/><Run Text="{Binding Label}"/>
+                      </TextBlock>
+                      <TextBlock Text="{Binding DisplayValue}" FontSize="11" Opacity="0.6"/>
+                    </StackPanel>
+                    <WrapPanel Grid.Column="1" HorizontalAlignment="Right">
+                      <ItemsControl ItemsSource="{Binding Choices}">
+                        <ItemsControl.ItemsPanel><ItemsPanelTemplate><StackPanel Orientation="Horizontal"/></ItemsPanelTemplate></ItemsControl.ItemsPanel>
+                        <ItemsControl.ItemTemplate>
+                          <DataTemplate x:DataType="vm:SeatRatingChoice">
+                            <Button Classes="choice" Classes.selected="{Binding IsSelected}"
+                                    Command="{Binding ApplyCommand}" Margin="2">
+                              <StackPanel>
+                                <TextBlock Text="{Binding Label}" HorizontalAlignment="Center" FontWeight="SemiBold"/>
+                                <TextBlock Text="{Binding Shortcut}" HorizontalAlignment="Center" FontSize="9" Opacity="0.5"/>
+                              </StackPanel>
+                            </Button>
+                          </DataTemplate>
+                        </ItemsControl.ItemTemplate>
+                      </ItemsControl>
+                      <Button Classes="choice" Content="−" Command="{Binding DecrementCommand}" Margin="2"/>
+                      <Button Classes="choice" Content="+" Command="{Binding IncrementCommand}" Margin="2"/>
+                      <Button Classes="choice" Content="Löschen" Command="{Binding ClearCommand}" Margin="2"/>
+                    </WrapPanel>
+                  </Grid>
+                </Border>
+              </DataTemplate>
+            </ItemsControl.ItemTemplate>
+          </ItemsControl>
+        </StackPanel>
+
+        <StackPanel Spacing="7">
+          <TextBlock Text="ANWESENHEIT" FontSize="11" FontWeight="Bold" Opacity="0.5"/>
+          <TextBlock Text="{Binding AttendanceLabel}" FontSize="12"/>
+          <ItemsControl ItemsSource="{Binding AttendanceChoices}">
+            <ItemsControl.ItemsPanel><ItemsPanelTemplate><WrapPanel/></ItemsPanelTemplate></ItemsControl.ItemsPanel>
+            <ItemsControl.ItemTemplate>
+              <DataTemplate x:DataType="vm:SeatAttendanceChoice">
+                <Button Classes="choice" Classes.selected="{Binding IsSelected}"
+                        Command="{Binding ApplyCommand}" Margin="2">
+                  <StackPanel Orientation="Horizontal" Spacing="5">
+                    <TextBlock Text="{Binding Symbol}" FontWeight="Bold"/>
+                    <TextBlock Text="{Binding Label}"/>
+                    <TextBlock Text="{Binding Shortcut}" FontSize="9" Opacity="0.5" VerticalAlignment="Center"/>
+                  </StackPanel>
+                </Button>
+              </DataTemplate>
+            </ItemsControl.ItemTemplate>
+          </ItemsControl>
+        </StackPanel>
+
+        <StackPanel Spacing="7">
+          <TextBlock Text="HAUSAUFGABEN" FontSize="11" FontWeight="Bold" Opacity="0.5"/>
+          <TextBlock Text="{Binding HomeworkLabel}" FontSize="12"/>
+          <ItemsControl ItemsSource="{Binding HomeworkChoices}">
+            <ItemsControl.ItemsPanel><ItemsPanelTemplate><WrapPanel/></ItemsPanelTemplate></ItemsControl.ItemsPanel>
+            <ItemsControl.ItemTemplate>
+              <DataTemplate x:DataType="vm:SeatHomeworkChoice">
+                <Button Classes="choice" Classes.selected="{Binding IsSelected}"
+                        Command="{Binding ApplyCommand}" Margin="2">
+                  <StackPanel Orientation="Horizontal" Spacing="5">
+                    <TextBlock Text="{Binding Symbol}" FontWeight="Bold"/>
+                    <TextBlock Text="{Binding Label}"/>
+                    <TextBlock Text="{Binding Shortcut}" FontSize="9" Opacity="0.5" VerticalAlignment="Center"/>
+                  </StackPanel>
+                </Button>
+              </DataTemplate>
+            </ItemsControl.ItemTemplate>
+          </ItemsControl>
+        </StackPanel>
+      </StackPanel>
+    </ScrollViewer>
+
+    <TextBlock Grid.Row="2" Margin="0,12,0,0" FontSize="10" Opacity="0.55" TextWrapping="Wrap"
+               Text="Mitarbeit: Q/W/E/R/T Aspekt · 1–5 Bewertung · +/− anpassen · Backspace löschen · ←/→ Aspekt  |  Anwesenheit: Strg+1/2/5/7/9/0, Strg+X  |  Hausaufgaben: ⌥+1/3/4/5/7/8/0, ⌥+X  |  Esc schließen"/>
+  </Grid>
+</Window>

LehrerApp.Desktop/Views/Groups/SeatAssessmentDialog.axaml.cs

@@ -0,0 +1,80 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using LehrerApp.Desktop.ViewModels.Groups;
+
+namespace LehrerApp.Desktop.Views.Groups;
+
+public partial class SeatAssessmentDialog : Window
+{
+    public SeatAssessmentDialog()
+    {
+        InitializeComponent();
+        AddHandler(KeyDownEvent, OnPreviewKeyDown, RoutingStrategies.Tunnel, handledEventsToo: true);
+    }
+
+    protected override void OnOpened(EventArgs e)
+    {
+        base.OnOpened(e);
+        Focus();
+    }
+
+    private void OnPreviewKeyDown(object? sender, KeyEventArgs e)
+    {
+        if (DataContext is not SeatAssessmentViewModel vm) return;
+        var digit = DigitFromEvent(e);
+        var clear = e.Key == Key.X || e.PhysicalKey == PhysicalKey.X;
+        if (e.KeyModifiers.HasFlag(KeyModifiers.Control))
+        {
+            if (clear || digit is not null) vm.ApplyAttendanceShortcut(digit, clear);
+            e.Handled = clear || digit is not null;
+            return;
+        }
+        if (e.KeyModifiers.HasFlag(KeyModifiers.Alt))
+        {
+            if (clear || digit is not null) vm.ApplyHomeworkShortcut(digit, clear);
+            e.Handled = clear || digit is not null;
+            return;
+        }
+        if (digit is not null)
+        {
+            vm.SetRatingByNumber(digit.Value);
+            e.Handled = true;
+            return;
+        }
+
+        switch (e.Key)
+        {
+            case Key.Q: vm.SelectAspect(0); e.Handled = true; break;
+            case Key.W: vm.SelectAspect(1); e.Handled = true; break;
+            case Key.E: vm.SelectAspect(2); e.Handled = true; break;
+            case Key.R: vm.SelectAspect(3); e.Handled = true; break;
+            case Key.T: vm.SelectAspect(4); e.Handled = true; break;
+            case Key.Left: vm.MoveAspect(-1); e.Handled = true; break;
+            case Key.Right: vm.MoveAspect(1); e.Handled = true; break;
+            case Key.OemPlus or Key.Add: vm.AdjustCurrentRating(1); e.Handled = true; break;
+            case Key.OemMinus or Key.Subtract: vm.AdjustCurrentRating(-1); e.Handled = true; break;
+            case Key.Back: vm.ClearCurrentRating(); e.Handled = true; break;
+            case Key.Escape: Close(); e.Handled = true; break;
+        }
+    }
+
+    private static int? DigitFromEvent(KeyEventArgs e) => e.PhysicalKey switch
+    {
+        PhysicalKey.Digit0 => 0, PhysicalKey.Digit1 => 1, PhysicalKey.Digit2 => 2,
+        PhysicalKey.Digit3 => 3, PhysicalKey.Digit4 => 4, PhysicalKey.Digit5 => 5,
+        PhysicalKey.Digit6 => 6, PhysicalKey.Digit7 => 7, PhysicalKey.Digit8 => 8,
+        PhysicalKey.Digit9 => 9,
+        _ => e.Key switch
+        {
+            Key.D0 or Key.NumPad0 => 0, Key.D1 or Key.NumPad1 => 1,
+            Key.D2 or Key.NumPad2 => 2, Key.D3 or Key.NumPad3 => 3,
+            Key.D4 or Key.NumPad4 => 4, Key.D5 or Key.NumPad5 => 5,
+            Key.D6 or Key.NumPad6 => 6, Key.D7 or Key.NumPad7 => 7,
+            Key.D8 or Key.NumPad8 => 8, Key.D9 or Key.NumPad9 => 9,
+            _ => null,
+        },
+    };
+
+    private void OnClose(object? sender, RoutedEventArgs e) => Close();
+}

LehrerApp.Desktop/Views/Groups/SeatingPlanTabView.axaml

@@ -3,6 +3,21 @@
              xmlns:vm="clr-namespace:LehrerApp.Desktop.ViewModels.Groups"
              x:Class="LehrerApp.Desktop.Views.Groups.SeatingPlanTabView"
              x:DataType="vm:SeatingPlanTabViewModel">
+  <UserControl.Styles>
+    <Style Selector="Border.seat">
+      <Setter Property="Background" Value="{DynamicResource SystemControlBackgroundAltHighBrush}"/>
+      <Setter Property="BorderBrush" Value="{DynamicResource SystemControlForegroundBaseLowBrush}"/>
+      <Setter Property="BorderThickness" Value="1"/>
+    </Style>
+    <Style Selector="Border.seat.occupied">
+      <Setter Property="BorderBrush" Value="{DynamicResource SystemAccentColor}"/>
+    </Style>
+    <Style Selector="Border.seat.droptarget">
+      <Setter Property="Background" Value="{DynamicResource SystemAccentColorLight2}"/>
+      <Setter Property="BorderBrush" Value="{DynamicResource SystemAccentColor}"/>
+      <Setter Property="BorderThickness" Value="2"/>
+    </Style>
+  </UserControl.Styles>
   <Grid ColumnDefinitions="260,*">
     <Border Grid.Column="0" BorderBrush="{DynamicResource SystemControlForegroundBaseLowBrush}"
             BorderThickness="0,0,1,0" Padding="16">
@@ -51,8 +66,11 @@
             <TextBlock Text="{Binding PlanTitle}" FontSize="22" FontWeight="SemiBold"/>
             <TextBlock Text="{Binding PlanSubtitle}" Opacity="0.65"/>
           </StackPanel>
-          <TextBlock Grid.Column="1" Text="{Binding AssignmentSummary}" VerticalAlignment="Bottom"
-                     FontSize="12" Opacity="0.6"/>
+          <StackPanel Grid.Column="1" VerticalAlignment="Bottom">
+            <TextBlock Text="{Binding AssignmentSummary}" HorizontalAlignment="Right" FontSize="12" Opacity="0.6"/>
+            <TextBlock Text="Ziehen: Platz ändern · Klicken: bewerten" HorizontalAlignment="Right"
+                       FontSize="11" Opacity="0.5"/>
+          </StackPanel>
         </Grid>
 
         <ScrollViewer Grid.Row="1" HorizontalScrollBarVisibility="Auto"
@@ -70,24 +88,60 @@
               </ItemsControl.ItemsPanel>
               <ItemsControl.ItemTemplate>
                 <DataTemplate x:DataType="vm:SeatCellViewModel">
-                  <Border Width="190" MinHeight="76" Margin="5" Padding="10"
-                          BorderBrush="{DynamicResource SystemControlForegroundBaseLowBrush}"
-                          BorderThickness="1" CornerRadius="7">
+                  <Border Classes="seat" Classes.occupied="{Binding IsOccupied}"
+                          Classes.droptarget="{Binding IsDropTarget}"
+                          Width="190" MinHeight="76" Margin="5" Padding="10"
+                          CornerRadius="7"
+                          DragDrop.AllowDrop="True"
+                          DragDrop.DragEnter="OnSeatDragEnter"
+                          DragDrop.DragLeave="OnSeatDragLeave"
+                          DragDrop.DragOver="OnSeatDragOver"
+                          DragDrop.Drop="OnSeatDrop"
+                          PointerPressed="OnDragSourcePressed"
+                          PointerMoved="OnDragSourceMoved"
+                          PointerReleased="OnDragSourceReleased"
+                          Tapped="OnSeatTapped">
                     <StackPanel Spacing="5">
-                      <TextBlock Text="{Binding PositionLabel}" FontSize="10" Opacity="0.5"/>
-                      <ComboBox ItemsSource="{Binding Options}" SelectedItem="{Binding SelectedOption}"
-                                IsEnabled="{Binding CanEdit}" HorizontalAlignment="Stretch">
-                        <ComboBox.ItemTemplate>
-                          <DataTemplate x:DataType="vm:StudentSeatOption">
-                            <TextBlock Text="{Binding DisplayName}"/>
-                          </DataTemplate>
-                        </ComboBox.ItemTemplate>
-                      </ComboBox>
+                      <Grid ColumnDefinitions="*,Auto">
+                        <TextBlock Text="{Binding PositionLabel}" FontSize="10" Opacity="0.5"/>
+                        <TextBlock Grid.Column="1" Text="⠿" Opacity="0.45" IsVisible="{Binding IsOccupied}"/>
+                      </Grid>
+                      <TextBlock Text="{Binding StudentName}" FontWeight="SemiBold" FontSize="13"
+                                 HorizontalAlignment="Center" VerticalAlignment="Center"/>
                     </StackPanel>
                   </Border>
                 </DataTemplate>
               </ItemsControl.ItemTemplate>
             </ItemsControl>
+
+            <Border DragDrop.AllowDrop="True" DragDrop.DragOver="OnUnassignedDragOver"
+                    DragDrop.Drop="OnUnassignedDrop"
+                    BorderBrush="{DynamicResource SystemControlForegroundBaseLowBrush}"
+                    BorderThickness="1" CornerRadius="7" Padding="12" Margin="5,8">
+              <StackPanel Spacing="8">
+                <TextBlock Text="NICHT ZUGEORDNET" FontSize="10" FontWeight="Bold" Opacity="0.5"/>
+                <TextBlock Text="Schüler hierher ziehen, um einen Platz zu leeren."
+                           FontSize="11" Opacity="0.5"/>
+                <ItemsControl ItemsSource="{Binding UnassignedStudents}">
+                  <ItemsControl.ItemsPanel>
+                    <ItemsPanelTemplate><WrapPanel/></ItemsPanelTemplate>
+                  </ItemsControl.ItemsPanel>
+                  <ItemsControl.ItemTemplate>
+                    <DataTemplate x:DataType="vm:StudentSeatOption">
+                      <Border Background="{DynamicResource SystemAccentColorLight2}" CornerRadius="5"
+                              Padding="9,5" Margin="0,0,6,6"
+                              PointerPressed="OnDragSourcePressed"
+                              PointerMoved="OnDragSourceMoved"
+                              PointerReleased="OnDragSourceReleased">
+                        <TextBlock Text="{Binding DisplayName}" FontSize="12"/>
+                      </Border>
+                    </DataTemplate>
+                  </ItemsControl.ItemTemplate>
+                </ItemsControl>
+                <TextBlock Text="Alle Schüler sind zugeordnet." Classes="emptyhint"
+                           IsVisible="{Binding !UnassignedStudents.Count}"/>
+              </StackPanel>
+            </Border>
           </StackPanel>
         </ScrollViewer>
       </Grid>

LehrerApp.Desktop/Views/Groups/SeatingPlanTabView.axaml.cs

@@ -1,4 +1,7 @@
 using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.Threading;
 using LehrerApp.Core.Models;
 using LehrerApp.Desktop.ViewModels.Groups;
 using LehrerApp.Desktop.Views.Shared;
@@ -7,6 +10,15 @@ namespace LehrerApp.Desktop.Views.Groups;
 
 public partial class SeatingPlanTabView : UserControl
 {
+    private object? _dragCandidate;
+    private PointerPressedEventArgs? _dragTrigger;
+    private Avalonia.Point _pressPosition;
+    private SeatCellViewModel? _draggedSeat;
+    private StudentSeatOption? _draggedStudent;
+    private SeatCellViewModel? _pendingDropTarget;
+    private bool _pendingClearSeat;
+    private DateTime _ignoreTapUntil;
+
     public SeatingPlanTabView() => InitializeComponent();
 
     protected override void OnDataContextChanged(EventArgs e)
@@ -16,9 +28,128 @@ public partial class SeatingPlanTabView : UserControl
         {
             vm.OnEditPlan = ShowPlanDialog;
             vm.OnConfirmDelete = ShowDeleteConfirmDialog;
+            vm.OnAssessStudent = ShowAssessmentDialog;
         }
     }
 
+    private void OnDragSourcePressed(object? sender, PointerPressedEventArgs e)
+    {
+        if (sender is not Control control ||
+            !e.GetCurrentPoint(control).Properties.IsLeftButtonPressed) return;
+        var candidate = control.DataContext;
+        if (candidate is SeatCellViewModel { IsOccupied: false } or null) return;
+        if (DataContext is not SeatingPlanTabViewModel { IsEditable: true }) return;
+        _dragCandidate = candidate;
+        _dragTrigger = e;
+        _pressPosition = e.GetPosition(this);
+    }
+
+    private async void OnDragSourceMoved(object? sender, PointerEventArgs e)
+    {
+        if (_dragCandidate is null || _dragTrigger is null ||
+            !e.GetCurrentPoint(this).Properties.IsLeftButtonPressed) return;
+        var current = e.GetPosition(this);
+        if (Math.Abs(current.X - _pressPosition.X) < 6 && Math.Abs(current.Y - _pressPosition.Y) < 6) return;
+
+        _draggedSeat = _dragCandidate as SeatCellViewModel;
+        _draggedStudent = _dragCandidate as StudentSeatOption;
+        _pendingDropTarget = null;
+        _pendingClearSeat = false;
+        _dragCandidate = null;
+        var trigger = _dragTrigger;
+        _dragTrigger = null;
+        var data = new DataTransfer();
+        data.Add(DataTransferItem.CreateText("LehrerApp-Sitzplatz"));
+        var effect = await DragDrop.DoDragDropAsync(trigger, data, DragDropEffects.Move);
+        var draggedSeat = _draggedSeat;
+        var draggedStudent = _draggedStudent;
+        var dropTarget = _pendingDropTarget;
+        var clearSeat = _pendingClearSeat;
+        _draggedSeat = null;
+        _draggedStudent = null;
+        _pendingDropTarget = null;
+        _pendingClearSeat = false;
+        _ignoreTapUntil = DateTime.UtcNow.AddMilliseconds(250);
+
+        // Never mutate an ItemsControl while Avalonia is still processing its native
+        // drop event. Assigning an unassigned student removes the dragged source item.
+        if ((effect & DragDropEffects.Move) == 0 || DataContext is not SeatingPlanTabViewModel vm) return;
+        Dispatcher.UIThread.Post(() =>
+        {
+            if (clearSeat && draggedSeat is not null) vm.ClearSeat(draggedSeat);
+            else if (dropTarget is not null && draggedSeat is not null) vm.MoveSeat(draggedSeat, dropTarget);
+            else if (dropTarget is not null && draggedStudent is not null) vm.AssignStudent(draggedStudent, dropTarget);
+        }, DispatcherPriority.Background);
+    }
+
+    private void OnDragSourceReleased(object? sender, PointerReleasedEventArgs e)
+    {
+        _dragCandidate = null;
+        _dragTrigger = null;
+    }
+
+    private void OnSeatDragEnter(object? sender, DragEventArgs e)
+    {
+        if (sender is Border { DataContext: SeatCellViewModel target } && CanDropOn(target))
+            target.IsDropTarget = true;
+    }
+
+    private void OnSeatDragLeave(object? sender, DragEventArgs e)
+    {
+        if (sender is Border { DataContext: SeatCellViewModel target }) target.IsDropTarget = false;
+    }
+
+    private void OnSeatDragOver(object? sender, DragEventArgs e)
+    {
+        e.DragEffects = sender is Border { DataContext: SeatCellViewModel target } && CanDropOn(target)
+            ? DragDropEffects.Move : DragDropEffects.None;
+    }
+
+    private void OnSeatDrop(object? sender, DragEventArgs e)
+    {
+        if (sender is not Border { DataContext: SeatCellViewModel target }) return;
+        target.IsDropTarget = false;
+        if (!CanDropOn(target))
+        {
+            e.DragEffects = DragDropEffects.None;
+            return;
+        }
+        _pendingDropTarget = target;
+        _pendingClearSeat = false;
+        e.DragEffects = DragDropEffects.Move;
+    }
+
+    private bool CanDropOn(SeatCellViewModel target) =>
+        DataContext is SeatingPlanTabViewModel { IsEditable: true }
+        && ((_draggedSeat is not null && _draggedSeat != target) || _draggedStudent?.StudentId is not null);
+
+    private void OnUnassignedDragOver(object? sender, DragEventArgs e) =>
+        e.DragEffects = _draggedSeat is not null ? DragDropEffects.Move : DragDropEffects.None;
+
+    private void OnUnassignedDrop(object? sender, DragEventArgs e)
+    {
+        if (_draggedSeat is not null)
+        {
+            _pendingDropTarget = null;
+            _pendingClearSeat = true;
+            e.DragEffects = DragDropEffects.Move;
+        }
+    }
+
+    private async void OnSeatTapped(object? sender, TappedEventArgs e)
+    {
+        if (DateTime.UtcNow < _ignoreTapUntil || sender is not Border { DataContext: SeatCellViewModel seat }
+            || !seat.IsOccupied || DataContext is not SeatingPlanTabViewModel vm) return;
+        await vm.AssessStudent(seat);
+    }
+
+    private async Task ShowAssessmentDialog(SeatAssessmentViewModel vm)
+    {
+        var dialog = new SeatAssessmentDialog { DataContext = vm };
+        var owner = TopLevel.GetTopLevel(this) as Window;
+        if (owner is not null) await dialog.ShowDialog(owner);
+    }
+
     private async Task<SeatingPlan?> ShowPlanDialog(SeatingPlan? plan)
     {
         if (DataContext is not SeatingPlanTabViewModel vm) return null;