diff --git a/src/ClaudeDo.Ui/Design/IslandStyles.axaml b/src/ClaudeDo.Ui/Design/IslandStyles.axaml
index a1817023..d19221c4 100644
--- a/src/ClaudeDo.Ui/Design/IslandStyles.axaml
+++ b/src/ClaudeDo.Ui/Design/IslandStyles.axaml
@@ -292,6 +292,23 @@
     <Setter Property="Foreground" Value="{StaticResource TextFaintBrush}" />
   </Style>
 
+  <!-- diff file tree: folders stay neutral, file icons take the change-kind colour via Tag (A/D/M/R) -->
+  <Style Selector="PathIcon.tree-icon">
+    <Setter Property="Foreground" Value="{StaticResource TextMuteBrush}" />
+  </Style>
+  <Style Selector="PathIcon.tree-icon[Tag=A]">
+    <Setter Property="Foreground" Value="{StaticResource MossBrush}" />
+  </Style>
+  <Style Selector="PathIcon.tree-icon[Tag=D]">
+    <Setter Property="Foreground" Value="{StaticResource BloodBrush}" />
+  </Style>
+  <Style Selector="PathIcon.tree-icon[Tag=M]">
+    <Setter Property="Foreground" Value="{StaticResource PeatBrush}" />
+  </Style>
+  <Style Selector="PathIcon.tree-icon[Tag=R]">
+    <Setter Property="Foreground" Value="{StaticResource SageBrush}" />
+  </Style>
+
   <!-- hover -->
   <Style Selector=".icon-btn:pointerover PathIcon, .new-list-btn:pointerover PathIcon">
     <Setter Property="Foreground" Value="{StaticResource TextBrush}" />
@@ -1071,6 +1088,19 @@
     <Setter Property="FontSize"   Value="{StaticResource FontSizeMono}" />
     <Setter Property="Foreground" Value="{StaticResource TextDimBrush}" />
   </Style>
+  <!-- diff file tree names: change-kind colour; must stay after TextBlock.meta -->
+  <Style Selector="TextBlock.tree-name[Tag=A]">
+    <Setter Property="Foreground" Value="{StaticResource MossBrush}" />
+  </Style>
+  <Style Selector="TextBlock.tree-name[Tag=D]">
+    <Setter Property="Foreground" Value="{StaticResource BloodBrush}" />
+  </Style>
+  <Style Selector="TextBlock.tree-name[Tag=M]">
+    <Setter Property="Foreground" Value="{StaticResource PeatBrush}" />
+  </Style>
+  <Style Selector="TextBlock.tree-name[Tag=R]">
+    <Setter Property="Foreground" Value="{StaticResource SageBrush}" />
+  </Style>
 
   <!-- Default body / list values / descriptions -->
   <Style Selector="TextBlock.body">
diff --git a/src/ClaudeDo.Ui/ViewModels/Modals/DiffModels.cs b/src/ClaudeDo.Ui/ViewModels/Modals/DiffModels.cs
index a6ab27eb..efac2389 100644
--- a/src/ClaudeDo.Ui/ViewModels/Modals/DiffModels.cs
+++ b/src/ClaudeDo.Ui/ViewModels/Modals/DiffModels.cs
@@ -1,5 +1,6 @@
 using System.Collections.ObjectModel;
 using CommunityToolkit.Mvvm.ComponentModel;
+using Material.Icons;
 
 namespace ClaudeDo.Ui.ViewModels.Modals;
 
@@ -63,7 +64,14 @@ public sealed partial class DiffTreeNodeViewModel : ViewModelBase
     public string RelativePath { get; init; } = "";
     public DiffFileViewModel? File { get; init; }
     public ObservableCollection<DiffTreeNodeViewModel> Children { get; } = new();
-    [ObservableProperty] private bool _isExpanded = true;
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(IconKey))]
+    private bool _isExpanded = true;
+
+    /// <summary>The row's <c>mdi:</c> icon key: open/closed folder, or the file-type icon.</summary>
+    public string IconKey => IsDirectory
+        ? (IsExpanded ? "mdi:FolderOpen" : "mdi:Folder")
+        : DiffFileIcons.ForPath(Name);
 
     public string? StatusCode => File?.StatusCode;
     public bool ShowStats => File is { IsBinary: false, IsPureRename: false };
@@ -71,6 +79,36 @@ public sealed partial class DiffTreeNodeViewModel : ViewModelBase
     public int Deletions => File?.Deletions ?? 0;
 }
 
+/// <summary>Maps a file name's extension to an <c>mdi:</c> icon key for the diff file tree.</summary>
+public static class DiffFileIcons
+{
+    private const MaterialIconKind Fallback = MaterialIconKind.FileOutline;
+
+    private static readonly Dictionary<string, MaterialIconKind> ByExtension = new(StringComparer.OrdinalIgnoreCase)
+    {
+        [".cs"] = MaterialIconKind.LanguageCsharp,
+        [".axaml"] = MaterialIconKind.CodeTags,
+        [".xaml"] = MaterialIconKind.CodeTags,
+        [".xml"] = MaterialIconKind.CodeTags,
+        [".json"] = MaterialIconKind.CodeJson,
+        [".md"] = MaterialIconKind.LanguageMarkdownOutline,
+        [".csproj"] = MaterialIconKind.FileCogOutline,
+        [".slnx"] = MaterialIconKind.FileCogOutline,
+        [".ps1"] = MaterialIconKind.Powershell,
+        [".sh"] = MaterialIconKind.Console,
+        [".png"] = MaterialIconKind.FileImageOutline,
+        [".jpg"] = MaterialIconKind.FileImageOutline,
+        [".jpeg"] = MaterialIconKind.FileImageOutline,
+        [".gif"] = MaterialIconKind.FileImageOutline,
+        [".svg"] = MaterialIconKind.FileImageOutline,
+        [".ico"] = MaterialIconKind.FileImageOutline,
+    };
+
+    /// <summary>Icon key for a file name or path; unknown or missing extensions fall back to a generic file.</summary>
+    public static string ForPath(string path) =>
+        "mdi:" + (ByExtension.TryGetValue(System.IO.Path.GetExtension(path), out var kind) ? kind : Fallback);
+}
+
 /// Builds a folder-grouped tree from a flat list of parsed diff files.
 public static class DiffTree
 {
diff --git a/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml b/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml
index b6664467..b31b190f 100644
--- a/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml
+++ b/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml
@@ -88,17 +88,20 @@
                 <TreeView.ItemTemplate>
                   <TreeDataTemplate DataType="vm:DiffTreeNodeViewModel" ItemsSource="{Binding Children}">
                     <Border Background="Transparent" Tapped="OnNodeTapped" Cursor="Hand" Padding="0,2">
-                      <Grid ColumnDefinitions="Auto,*,Auto">
-                        <Border Grid.Column="0" Tag="{Binding StatusCode}" CornerRadius="3" Padding="4,0" Margin="0,0,6,0"
+                      <Grid ColumnDefinitions="Auto,Auto,*,Auto">
+                        <PathIcon Grid.Column="0" Classes="tree-icon" Width="14" Height="14" Margin="0,0,6,0"
+                                  Tag="{Binding StatusCode}"
+                                  Data="{Binding IconKey, Converter={StaticResource IconKey}}"/>
+                        <Border Grid.Column="1" Tag="{Binding StatusCode}" CornerRadius="3" Padding="4,0" Margin="0,0,6,0"
                                 VerticalAlignment="Center"
                                 IsVisible="{Binding StatusCode, Converter={x:Static StringConverters.IsNotNullOrEmpty}}">
                           <TextBlock Text="{Binding StatusCode}"
                                      FontFamily="{DynamicResource MonoFont}" FontSize="{StaticResource FontSizeEyebrow}"
                                      Foreground="{DynamicResource TextBrush}"/>
                         </Border>
-                        <TextBlock Grid.Column="1" Classes="meta" Text="{Binding Name}"
+                        <TextBlock Grid.Column="2" Classes="meta tree-name" Text="{Binding Name}" Tag="{Binding StatusCode}"
                                    VerticalAlignment="Center" TextTrimming="CharacterEllipsis"/>
-                        <StackPanel Grid.Column="2" Orientation="Horizontal" Spacing="4" VerticalAlignment="Center"
+                        <StackPanel Grid.Column="3" Orientation="Horizontal" Spacing="4" VerticalAlignment="Center"
                                     Margin="0,0,8,0"
                                     IsVisible="{Binding ShowStats}">
                           <TextBlock Foreground="{DynamicResource MossBrightBrush}" FontSize="{StaticResource FontSizeEyebrow}"
diff --git a/tests/ClaudeDo.Ui.Tests/DiffFileIconsTests.cs b/tests/ClaudeDo.Ui.Tests/DiffFileIconsTests.cs
new file mode 100644
index 00000000..7d82aaa7
--- /dev/null
+++ b/tests/ClaudeDo.Ui.Tests/DiffFileIconsTests.cs
@@ -0,0 +1,43 @@
+using ClaudeDo.Ui.ViewModels.Modals;
+
+namespace ClaudeDo.Ui.Tests;
+
+public class DiffFileIconsTests
+{
+    [Theory]
+    [InlineData("src/Foo.cs", "mdi:LanguageCsharp")]
+    [InlineData("Views/A.axaml", "mdi:CodeTags")]
+    [InlineData("a.xaml", "mdi:CodeTags")]
+    [InlineData("a.xml", "mdi:CodeTags")]
+    [InlineData("package.json", "mdi:CodeJson")]
+    [InlineData("README.md", "mdi:LanguageMarkdownOutline")]
+    [InlineData("X.csproj", "mdi:FileCogOutline")]
+    [InlineData("ClaudeDo.slnx", "mdi:FileCogOutline")]
+    [InlineData("run.ps1", "mdi:Powershell")]
+    [InlineData("build.sh", "mdi:Console")]
+    [InlineData("logo.png", "mdi:FileImageOutline")]
+    public void ForPath_MapsKnownExtensions(string path, string expected)
+        => Assert.Equal(expected, DiffFileIcons.ForPath(path));
+
+    [Theory]
+    [InlineData("Foo.CS")]
+    [InlineData("A.AXAML")]
+    public void ForPath_IsCaseInsensitive(string path)
+        => Assert.NotEqual("mdi:FileOutline", DiffFileIcons.ForPath(path));
+
+    [Theory]
+    [InlineData("Dockerfile")]
+    [InlineData("notes.unknownext")]
+    [InlineData("")]
+    public void ForPath_FallsBackToGenericFile(string path)
+        => Assert.Equal("mdi:FileOutline", DiffFileIcons.ForPath(path));
+
+    [Fact]
+    public void FolderIcon_FollowsIsExpanded()
+    {
+        var dir = new DiffTreeNodeViewModel { Name = "src", IsDirectory = true };
+        Assert.Equal("mdi:FolderOpen", dir.IconKey);
+        dir.IsExpanded = false;
+        Assert.Equal("mdi:Folder", dir.IconKey);
+    }
+}