diff --git a/src/ClaudeDo.Data/Git/GitService.cs b/src/ClaudeDo.Data/Git/GitService.cs
index 673583f..29c34e6 100644
--- a/src/ClaudeDo.Data/Git/GitService.cs
+++ b/src/ClaudeDo.Data/Git/GitService.cs
@@ -106,6 +106,15 @@ public sealed class GitService
         return stdout.Trim();
     }
 
+    public async Task<string> GetFileDiffAsync(string worktreePath, string? baseCommit, string relativePath, CancellationToken ct = default)
+    {
+        string[] args = string.IsNullOrEmpty(baseCommit)
+            ? ["diff", "--", relativePath]
+            : ["diff", $"{baseCommit}..HEAD", "--", relativePath];
+        var (_, stdout, _) = await RunGitAsync(worktreePath, args, ct);
+        return stdout;
+    }
+
     public async Task WorktreeRemoveAsync(string repoDir, string worktreePath, bool force = false, CancellationToken ct = default)
     {
         var args = new List<string> { "worktree", "remove" };
diff --git a/src/ClaudeDo.Ui/ViewModels/Modals/WorktreeModalViewModel.cs b/src/ClaudeDo.Ui/ViewModels/Modals/WorktreeModalViewModel.cs
index 19d6e90..d0d1492 100644
--- a/src/ClaudeDo.Ui/ViewModels/Modals/WorktreeModalViewModel.cs
+++ b/src/ClaudeDo.Ui/ViewModels/Modals/WorktreeModalViewModel.cs
@@ -10,6 +10,7 @@ public sealed partial class WorktreeNodeViewModel : ViewModelBase
     public required string Name { get; init; }
     public string? Status { get; init; }
     public bool IsDirectory { get; init; }
+    public string RelativePath { get; init; } = "";
     public ObservableCollection<WorktreeNodeViewModel> Children { get; } = new();
 }
 
@@ -21,6 +22,8 @@ public sealed partial class WorktreeModalViewModel : ViewModelBase
 
     [ObservableProperty] private string _worktreePath = "";
     [ObservableProperty] private string? _baseCommit;
+    [ObservableProperty] private WorktreeNodeViewModel? _selectedNode;
+    [ObservableProperty] private string _selectedFileDiff = "";
 
     // Set by the view (same pattern as DiffModalViewModel.CloseAction)
     public Action? CloseAction { get; set; }
@@ -30,6 +33,29 @@ public sealed partial class WorktreeModalViewModel : ViewModelBase
         _git = git;
     }
 
+    partial void OnSelectedNodeChanged(WorktreeNodeViewModel? value)
+    {
+        _ = LoadFileDiffAsync(value);
+    }
+
+    private async Task LoadFileDiffAsync(WorktreeNodeViewModel? node)
+    {
+        if (node is null || node.IsDirectory || string.IsNullOrEmpty(node.RelativePath))
+        {
+            SelectedFileDiff = "";
+            return;
+        }
+
+        try
+        {
+            SelectedFileDiff = await _git.GetFileDiffAsync(WorktreePath, BaseCommit, node.RelativePath);
+        }
+        catch
+        {
+            SelectedFileDiff = "";
+        }
+    }
+
     [RelayCommand]
     private void Close() => CloseAction?.Invoke();
 
@@ -97,7 +123,8 @@ public sealed partial class WorktreeModalViewModel : ViewModelBase
             {
                 Name = segments[^1],
                 Status = status,
-                IsDirectory = false
+                IsDirectory = false,
+                RelativePath = path
             };
             if (parent == null) Root.Add(leaf);
             else parent.Children.Add(leaf);
diff --git a/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml b/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml
index 444fcb4..0bbf09a 100644
--- a/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml
+++ b/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml
@@ -4,12 +4,13 @@
         x:Class="ClaudeDo.Ui.Views.Modals.WorktreeModalView"
         x:DataType="vm:WorktreeModalViewModel"
         Title="Worktree"
-        Width="640" Height="720"
+        Width="1100" Height="720"
+        MinWidth="640" MinHeight="400"
         WindowStartupLocation="CenterOwner"
         SystemDecorations="None"
         ExtendClientAreaToDecorationsHint="True"
         Background="Transparent"
-        CanResize="False"
+        CanResize="True"
         TransparencyLevelHint="AcrylicBlur">
 
   <Window.KeyBindings>
@@ -39,27 +40,51 @@
                    TextTrimming="CharacterEllipsis"/>
       </Border>
 
-      <!-- File tree -->
-      <TreeView DockPanel.Dock="Top" ItemsSource="{Binding Root}"
-                Background="Transparent" Margin="8,0,8,8">
-        <TreeView.ItemTemplate>
-          <TreeDataTemplate DataType="vm:WorktreeNodeViewModel"
-                            ItemsSource="{Binding Children}">
-            <StackPanel Orientation="Horizontal" Spacing="8">
-              <TextBlock Text="{Binding Name}"
-                         FontFamily="{DynamicResource MonoFont}" FontSize="12"
-                         Foreground="{DynamicResource TextBrush}"/>
-              <Border Tag="{Binding Status}" CornerRadius="3" Padding="4,0"
-                      VerticalAlignment="Center"
-                      IsVisible="{Binding Status, Converter={x:Static ObjectConverters.IsNotNull}}">
-                <TextBlock Text="{Binding Status}"
-                           FontFamily="{DynamicResource MonoFont}" FontSize="10"
+      <!-- Split: file tree | splitter | diff pane -->
+      <Grid ColumnDefinitions="260,4,*">
+
+        <!-- Left: file tree -->
+        <TreeView x:Name="FileTree"
+                  Grid.Column="0"
+                  ItemsSource="{Binding Root}"
+                  SelectedItem="{Binding SelectedNode, Mode=TwoWay}"
+                  Background="Transparent"
+                  Margin="8,0,4,8">
+          <TreeView.ItemTemplate>
+            <TreeDataTemplate DataType="vm:WorktreeNodeViewModel"
+                              ItemsSource="{Binding Children}">
+              <StackPanel Orientation="Horizontal" Spacing="8">
+                <TextBlock Text="{Binding Name}"
+                           FontFamily="{DynamicResource MonoFont}" FontSize="12"
                            Foreground="{DynamicResource TextBrush}"/>
-              </Border>
-            </StackPanel>
-          </TreeDataTemplate>
-        </TreeView.ItemTemplate>
-      </TreeView>
+                <Border Tag="{Binding Status}" CornerRadius="3" Padding="4,0"
+                        VerticalAlignment="Center"
+                        IsVisible="{Binding Status, Converter={x:Static ObjectConverters.IsNotNull}}">
+                  <TextBlock Text="{Binding Status}"
+                             FontFamily="{DynamicResource MonoFont}" FontSize="10"
+                             Foreground="{DynamicResource TextBrush}"/>
+                </Border>
+              </StackPanel>
+            </TreeDataTemplate>
+          </TreeView.ItemTemplate>
+        </TreeView>
+
+        <!-- Splitter -->
+        <GridSplitter Grid.Column="1" ResizeDirection="Columns" Background="{DynamicResource LineBrush}"/>
+
+        <!-- Right: diff content -->
+        <ScrollViewer Grid.Column="2" Padding="8"
+                      HorizontalScrollBarVisibility="Auto"
+                      VerticalScrollBarVisibility="Auto"
+                      Margin="4,0,8,8">
+          <SelectableTextBlock Text="{Binding SelectedFileDiff}"
+                               FontFamily="{DynamicResource MonoFont}"
+                               FontSize="11"
+                               Foreground="{DynamicResource TextBrush}"
+                               TextWrapping="NoWrap"/>
+        </ScrollViewer>
+
+      </Grid>
 
     </DockPanel>
   </Border>
diff --git a/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml.cs b/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml.cs
index bb650ea..da5aa2b 100644
--- a/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml.cs
+++ b/src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml.cs
@@ -21,6 +21,18 @@ public partial class WorktreeModalView : Window
         base.OnDataContextChanged(e);
         if (DataContext is WorktreeModalViewModel vm)
             vm.CloseAction = Close;
+
+        // Wire TreeView selection — SelectedItem TwoWay binding may not fire
+        // reliably in Avalonia 12 for TreeView; use SelectionChanged as backup.
+        var tree = this.FindControl<TreeView>("FileTree");
+        if (tree is not null)
+            tree.SelectionChanged += OnFileTreeSelectionChanged;
+    }
+
+    private void OnFileTreeSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is WorktreeModalViewModel vm && sender is TreeView tree)
+            vm.SelectedNode = tree.SelectedItem as WorktreeNodeViewModel;
     }
 
     protected override async void OnOpened(EventArgs e)
diff --git a/src/ClaudeDo.Ui/Views/Modals/WorktreesOverviewModalView.axaml b/src/ClaudeDo.Ui/Views/Modals/WorktreesOverviewModalView.axaml
index 53ec248..cbf552a 100644
--- a/src/ClaudeDo.Ui/Views/Modals/WorktreesOverviewModalView.axaml
+++ b/src/ClaudeDo.Ui/Views/Modals/WorktreesOverviewModalView.axaml
@@ -8,7 +8,7 @@
         Width="900" Height="560" MinWidth="640" MinHeight="360"
         CanResize="True"
         WindowStartupLocation="CenterOwner"
-        Background="{DynamicResource VoidBrush}"
+        Background="{DynamicResource SurfaceBrush}"
         SystemDecorations="None"
         ExtendClientAreaToDecorationsHint="True">
 
@@ -104,10 +104,7 @@
     </Style>
   </Window.Styles>
 
-  <Border Background="{DynamicResource SurfaceBrush}"
-          BorderBrush="{DynamicResource LineBrush}"
-          BorderThickness="1">
-    <Grid RowDefinitions="36,Auto,*,52">
+  <Grid RowDefinitions="36,Auto,*,52">
 
       <!-- Title bar -->
       <Border Grid.Row="0"
@@ -208,5 +205,4 @@
       </Border>
 
     </Grid>
-  </Border>
 </Window>