refactor(ui): share color-coded diff rendering between per-task and combined diff viewers

Extract the unified-diff parser into UnifiedDiffParser and the styled line
renderer into a reusable DiffLinesView control. The combined (planning) diff
now parses its unified-diff string and renders color-coded rows (green
additions / red deletions, file headers) identical to the per-task viewer
instead of dumping plain text into a TextBox.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ClaudeDo.Ui/ViewModels/Modals/DiffModalViewModel.cs

@@ -6,7 +6,7 @@ using ClaudeDo.Ui.Localization;
 
 namespace ClaudeDo.Ui.ViewModels.Modals;
 
-public enum DiffLineKind { Add, Del, Ctx }
+public enum DiffLineKind { Add, Del, Ctx, File }
 
 public sealed class DiffLineViewModel
 {
@@ -18,6 +18,7 @@ public sealed class DiffLineViewModel
     {
         DiffLineKind.Add  => "add",
         DiffLineKind.Del  => "del",
+        DiffLineKind.File => "file",
         _                 => "ctx",
     };
 
@@ -102,90 +103,10 @@ public sealed partial class DiffModalViewModel : ViewModelBase
             return;
         }
 
-        // Parse unified diff — state machine over lines
+        foreach (var file in UnifiedDiffParser.Parse(raw))
-        DiffFileViewModel? current = null;
+            Files.Add(file);
-        int oldLine = 0, newLine = 0;
-
-        foreach (var line in raw.Split('\n'))
-        {
-            if (line.StartsWith("diff --git ", StringComparison.Ordinal))
-            {
-                // e.g. "diff --git a/src/Foo.cs b/src/Foo.cs"
-                var parts = line.Split(' ');
-                var path = parts.Length >= 4 ? parts[3][2..] : line;
-                current = new DiffFileViewModel { Path = path };
-                Files.Add(current);
-                oldLine = 0; newLine = 0;
-                continue;
-            }
-
-            if (current == null) continue;
-
-            if (line.StartsWith("@@ ", StringComparison.Ordinal))
-            {
-                // e.g. "@@ -10,7 +10,9 @@"
-                ParseHunkHeader(line, out oldLine, out newLine);
-                continue;
-            }
-
-            // Skip diff metadata lines
-            if (line.StartsWith("--- ", StringComparison.Ordinal) ||
-                line.StartsWith("+++ ", StringComparison.Ordinal) ||
-                line.StartsWith("index ", StringComparison.Ordinal) ||
-                line.StartsWith("new file", StringComparison.Ordinal) ||
-                line.StartsWith("deleted file", StringComparison.Ordinal) ||
-                line.StartsWith("Binary ", StringComparison.Ordinal))
-                continue;
-
-            if (line.StartsWith('+'))
-            {
-                current.Lines.Add(new DiffLineViewModel
-                {
-                    Kind = DiffLineKind.Add,
-                    NewNo = newLine++,
-                    Text = line.Length > 1 ? line[1..] : "",
-                });
-                current.Additions++;
-            }
-            else if (line.StartsWith('-'))
-            {
-                current.Lines.Add(new DiffLineViewModel
-                {
-                    Kind = DiffLineKind.Del,
-                    OldNo = oldLine++,
-                    Text = line.Length > 1 ? line[1..] : "",
-                });
-                current.Deletions++;
-            }
-            else if (line.StartsWith(' '))
-            {
-                current.Lines.Add(new DiffLineViewModel
-                {
-                    Kind = DiffLineKind.Ctx,
-                    OldNo = oldLine++,
-                    NewNo = newLine++,
-                    Text = line.Length > 1 ? line[1..] : "",
-                });
-            }
-        }
 
         SelectedFile = Files.Count > 0 ? Files[0] : null;
         if (Files.Count == 0) StatusMessage = Loc.T("vm.diff.noChanges");
     }
-
-    private static void ParseHunkHeader(string header, out int oldStart, out int newStart)
-    {
-        oldStart = 1; newStart = 1;
-        // Format: @@ -<old>,<count> +<new>,<count> @@
-        var at = header.IndexOf("@@", 3, StringComparison.Ordinal);
-        var inner = at > 0 ? header[3..at].Trim() : header;
-        var segs = inner.Split(' ');
-        foreach (var seg in segs)
-        {
-            if (seg.StartsWith('-') && int.TryParse(seg[1..].Split(',')[0], out var o))
-                oldStart = o;
-            else if (seg.StartsWith('+') && int.TryParse(seg[1..].Split(',')[0], out var n))
-                newStart = n;
-        }
-    }
 }

src/ClaudeDo.Ui/ViewModels/Modals/UnifiedDiffParser.cs

@@ -0,0 +1,111 @@
+namespace ClaudeDo.Ui.ViewModels.Modals;
+
+/// Shared unified-diff parser used by both the per-task diff viewer and the
+/// combined (planning) diff viewer so they render identically.
+public static class UnifiedDiffParser
+{
+    public static List<DiffFileViewModel> Parse(string? raw)
+    {
+        var files = new List<DiffFileViewModel>();
+        if (string.IsNullOrWhiteSpace(raw)) return files;
+
+        DiffFileViewModel? current = null;
+        int oldLine = 0, newLine = 0;
+
+        foreach (var line in raw.Split('\n'))
+        {
+            if (line.StartsWith("diff --git ", StringComparison.Ordinal))
+            {
+                // e.g. "diff --git a/src/Foo.cs b/src/Foo.cs"
+                var parts = line.Split(' ');
+                var path = parts.Length >= 4 ? parts[3][2..] : line;
+                current = new DiffFileViewModel { Path = path };
+                files.Add(current);
+                oldLine = 0; newLine = 0;
+                continue;
+            }
+
+            if (current == null) continue;
+
+            if (line.StartsWith("@@ ", StringComparison.Ordinal))
+            {
+                // e.g. "@@ -10,7 +10,9 @@"
+                ParseHunkHeader(line, out oldLine, out newLine);
+                continue;
+            }
+
+            // Skip diff metadata lines
+            if (line.StartsWith("--- ", StringComparison.Ordinal) ||
+                line.StartsWith("+++ ", StringComparison.Ordinal) ||
+                line.StartsWith("index ", StringComparison.Ordinal) ||
+                line.StartsWith("new file", StringComparison.Ordinal) ||
+                line.StartsWith("deleted file", StringComparison.Ordinal) ||
+                line.StartsWith("Binary ", StringComparison.Ordinal))
+                continue;
+
+            if (line.StartsWith('+'))
+            {
+                current.Lines.Add(new DiffLineViewModel
+                {
+                    Kind = DiffLineKind.Add,
+                    NewNo = newLine++,
+                    Text = line.Length > 1 ? line[1..] : "",
+                });
+                current.Additions++;
+            }
+            else if (line.StartsWith('-'))
+            {
+                current.Lines.Add(new DiffLineViewModel
+                {
+                    Kind = DiffLineKind.Del,
+                    OldNo = oldLine++,
+                    Text = line.Length > 1 ? line[1..] : "",
+                });
+                current.Deletions++;
+            }
+            else if (line.StartsWith(' '))
+            {
+                current.Lines.Add(new DiffLineViewModel
+                {
+                    Kind = DiffLineKind.Ctx,
+                    OldNo = oldLine++,
+                    NewNo = newLine++,
+                    Text = line.Length > 1 ? line[1..] : "",
+                });
+            }
+        }
+
+        return files;
+    }
+
+    /// Flattens multiple parsed files into a single line stream, inserting a
+    /// file-header row before each file so boundaries are visible in a
+    /// single-pane (combined) view.
+    public static List<DiffLineViewModel> Flatten(IEnumerable<DiffFileViewModel> files)
+    {
+        var lines = new List<DiffLineViewModel>();
+        foreach (var file in files)
+        {
+            lines.Add(new DiffLineViewModel { Kind = DiffLineKind.File, Text = file.Path });
+            foreach (var line in file.Lines)
+                lines.Add(line);
+        }
+        return lines;
+    }
+
+    private static void ParseHunkHeader(string header, out int oldStart, out int newStart)
+    {
+        oldStart = 1; newStart = 1;
+        // Format: @@ -<old>,<count> +<new>,<count> @@
+        var at = header.IndexOf("@@", 3, StringComparison.Ordinal);
+        var inner = at > 0 ? header[3..at].Trim() : header;
+        var segs = inner.Split(' ');
+        foreach (var seg in segs)
+        {
+            if (seg.StartsWith('-') && int.TryParse(seg[1..].Split(',')[0], out var o))
+                oldStart = o;
+            else if (seg.StartsWith('+') && int.TryParse(seg[1..].Split(',')[0], out var n))
+                newStart = n;
+        }
+    }
+}

src/ClaudeDo.Ui/ViewModels/Planning/PlanningDiffViewModel.cs

@@ -3,6 +3,7 @@ using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using ClaudeDo.Ui.Localization;
 using ClaudeDo.Ui.Services;
+using ClaudeDo.Ui.ViewModels.Modals;
 
 namespace ClaudeDo.Ui.ViewModels.Planning;
 
@@ -13,6 +14,7 @@ public sealed partial class PlanningDiffViewModel : ObservableObject
     private readonly string _targetBranch;
 
     public ObservableCollection<SubtaskDiffRow> Subtasks { get; } = new();
+    public ObservableCollection<DiffLineViewModel> DiffLines { get; } = new();
 
     [ObservableProperty] private SubtaskDiffRow? _selectedSubtask;
     [ObservableProperty] private string _displayedDiff = "";
@@ -87,6 +89,13 @@ public sealed partial class PlanningDiffViewModel : ObservableObject
     }
 
     partial void OnIsCombinedModeChanged(bool value) => ToggleCombinedCommand.Execute(null);
+
+    partial void OnDisplayedDiffChanged(string value)
+    {
+        DiffLines.Clear();
+        foreach (var line in UnifiedDiffParser.Flatten(UnifiedDiffParser.Parse(value)))
+            DiffLines.Add(line);
+    }
 }
 
 public sealed record SubtaskDiffRow(string Id, string Title, string? DiffStat, string UnifiedDiff);

src/ClaudeDo.Ui/Views/Controls/DiffLinesView.axaml

@@ -0,0 +1,82 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ClaudeDo.Ui.ViewModels.Modals"
+             x:Class="ClaudeDo.Ui.Views.Controls.DiffLinesView"
+             x:Name="Root">
+
+  <UserControl.Styles>
+    <!-- diff line row tints via Tag selector (compiled-binding-friendly) -->
+    <Style Selector="Border.diff-line[Tag=add]">
+      <Setter Property="Background" Value="{StaticResource RunningTintBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=del]">
+      <Setter Property="Background" Value="{StaticResource ErrorTintBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=ctx]">
+      <Setter Property="Background" Value="Transparent"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=file]">
+      <Setter Property="Background" Value="{StaticResource Surface3Brush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-sign">
+      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-sign">
+      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-sign">
+      <Setter Property="Foreground" Value="{StaticResource TextFaintBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource TextDimBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=file] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource TextBrush}"/>
+      <Setter Property="FontWeight" Value="SemiBold"/>
+    </Style>
+  </UserControl.Styles>
+
+  <ItemsControl ItemsSource="{Binding #Root.Lines}">
+    <ItemsControl.ItemTemplate>
+      <DataTemplate x:DataType="vm:DiffLineViewModel">
+        <Border Classes="diff-line"
+                Tag="{Binding ClassName}"
+                Padding="4,1">
+          <Grid ColumnDefinitions="48,48,16,*">
+            <!-- Old line number -->
+            <TextBlock Grid.Column="0"
+                       Text="{Binding OldNo}"
+                       Classes="diff-lineno"
+                       HorizontalAlignment="Right"
+                       Margin="0,0,8,0"/>
+            <!-- New line number -->
+            <TextBlock Grid.Column="1"
+                       Text="{Binding NewNo}"
+                       Classes="diff-lineno"
+                       HorizontalAlignment="Right"
+                       Margin="0,0,8,0"/>
+            <!-- Sign -->
+            <TextBlock Grid.Column="2"
+                       Classes="diff-sign"
+                       Text="{Binding Sign}"
+                       FontFamily="{DynamicResource MonoFont}"
+                       FontSize="{StaticResource FontSizeMono}"/>
+            <!-- Line text -->
+            <TextBlock Grid.Column="3"
+                       Classes="diff-text"
+                       Text="{Binding Text}"
+                       FontFamily="{DynamicResource MonoFont}"
+                       FontSize="{StaticResource FontSizeMono}"
+                       TextWrapping="NoWrap"/>
+          </Grid>
+        </Border>
+      </DataTemplate>
+    </ItemsControl.ItemTemplate>
+  </ItemsControl>
+</UserControl>

src/ClaudeDo.Ui/Views/Controls/DiffLinesView.axaml.cs

@@ -0,0 +1,19 @@
+using System.Collections;
+using Avalonia;
+using Avalonia.Controls;
+
+namespace ClaudeDo.Ui.Views.Controls;
+
+public partial class DiffLinesView : UserControl
+{
+    public static readonly StyledProperty<IEnumerable?> LinesProperty =
+        AvaloniaProperty.Register<DiffLinesView, IEnumerable?>(nameof(Lines));
+
+    public IEnumerable? Lines
+    {
+        get => GetValue(LinesProperty);
+        set => SetValue(LinesProperty, value);
+    }
+
+    public DiffLinesView() => InitializeComponent();
+}

src/ClaudeDo.Ui/Views/Modals/DiffModalView.axaml

@@ -18,37 +18,6 @@
     <KeyBinding Gesture="Escape" Command="{Binding CloseCommand}"/>
   </Window.KeyBindings>
 
-  <Window.Styles>
-    <!-- diff line row tints via Tag selector (compiled-binding-friendly) -->
-    <Style Selector="Border.diff-line[Tag=add]">
-      <Setter Property="Background" Value="{StaticResource RunningTintBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=del]">
-      <Setter Property="Background" Value="{StaticResource ErrorTintBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=ctx]">
-      <Setter Property="Background" Value="Transparent"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-sign">
-      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-sign">
-      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-sign">
-      <Setter Property="Foreground" Value="{StaticResource TextFaintBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-text">
-      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-text">
-      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-text">
-      <Setter Property="Foreground" Value="{StaticResource TextDimBrush}"/>
-    </Style>
-  </Window.Styles>
-
   <ctl:ModalShell Title="{loc:Tr modals.diff.title}" CloseCommand="{Binding CloseCommand}">
     <ctl:ModalShell.Footer>
       <StackPanel Orientation="Horizontal" Spacing="8"
@@ -99,43 +68,7 @@
                    VerticalAlignment="Center"/>
         <ScrollViewer HorizontalScrollBarVisibility="Auto"
                     VerticalScrollBarVisibility="Auto">
-        <ItemsControl ItemsSource="{Binding SelectedFile.Lines}">
+          <ctl:DiffLinesView Lines="{Binding SelectedFile.Lines}"/>
-          <ItemsControl.ItemTemplate>
-            <DataTemplate x:DataType="vm:DiffLineViewModel">
-              <Border Classes="diff-line"
-                      Tag="{Binding ClassName}"
-                      Padding="4,1">
-                <Grid ColumnDefinitions="48,48,16,*">
-                  <!-- Old line number -->
-                  <TextBlock Grid.Column="0"
-                             Text="{Binding OldNo}"
-                             Classes="diff-lineno"
-                             HorizontalAlignment="Right"
-                             Margin="0,0,8,0"/>
-                  <!-- New line number -->
-                  <TextBlock Grid.Column="1"
-                             Text="{Binding NewNo}"
-                             Classes="diff-lineno"
-                             HorizontalAlignment="Right"
-                             Margin="0,0,8,0"/>
-                  <!-- Sign -->
-                  <TextBlock Grid.Column="2"
-                             Classes="diff-sign"
-                             Text="{Binding Sign}"
-                             FontFamily="{DynamicResource MonoFont}"
-                             FontSize="{StaticResource FontSizeMono}"/>
-                  <!-- Line text -->
-                  <TextBlock Grid.Column="3"
-                             Classes="diff-text"
-                             Text="{Binding Text}"
-                             FontFamily="{DynamicResource MonoFont}"
-                             FontSize="{StaticResource FontSizeMono}"
-                             TextWrapping="NoWrap"/>
-                </Grid>
-              </Border>
-            </DataTemplate>
-          </ItemsControl.ItemTemplate>
-        </ItemsControl>
         </ScrollViewer>
       </Grid>
     </Grid>

src/ClaudeDo.Ui/Views/Planning/PlanningDiffView.axaml

@@ -66,14 +66,7 @@
         <Grid Grid.Column="1" Background="{DynamicResource VoidBrush}">
           <ScrollViewer HorizontalScrollBarVisibility="Auto"
                         VerticalScrollBarVisibility="Auto">
-            <TextBox Text="{Binding DisplayedDiff, Mode=OneWay}"
+            <ctl:DiffLinesView Lines="{Binding DiffLines}"/>
-                     IsReadOnly="True"
-                     AcceptsReturn="True"
-                     FontFamily="{DynamicResource MonoFont}"
-                     FontSize="{StaticResource FontSizeBody}"
-                     Background="Transparent"
-                     BorderThickness="0"
-                     Padding="8"/>
           </ScrollViewer>
         </Grid>