feat(diff): add persisted side-by-side and wrap toggles to the diff viewer

src/ClaudeDo.Localization/locales/de.json

@@ -357,7 +357,9 @@
       "merge": "Mergen…",
       "filesHeader": "Dateien",
       "binary": "Binärdatei — kein Text-Diff",
-      "empty": "Kein Inhalt"
+      "empty": "Kein Inhalt",
+      "splitView": "Nebeneinander",
+      "wrapLines": "Zeilenumbruch"
     },
     "worktreesOverview": {
       "refresh": "Aktualisieren",

src/ClaudeDo.Localization/locales/en.json

@@ -357,7 +357,9 @@
       "merge": "Merge…",
       "filesHeader": "Files",
       "binary": "Binary file — no text diff",
-      "empty": "No content"
+      "empty": "No content",
+      "splitView": "Side by side",
+      "wrapLines": "Wrap lines"
     },
     "worktreesOverview": {
       "refresh": "Refresh",

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

@@ -1,7 +1,10 @@
+using System;
 using System.Collections.ObjectModel;
+using System.IO;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using ClaudeDo.Data.Git;
+using ClaudeDo.Ui;
 using ClaudeDo.Ui.Localization;
 using ClaudeDo.Ui.Services;
 
@@ -21,6 +24,7 @@ public sealed partial class DiffViewerViewModel : ViewModelBase
 {
     private readonly GitService _git;
     private readonly IWorkerClient _worker;
+    private readonly AppSettings _settings;
 
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(IsPlanning))]
@@ -56,6 +60,31 @@ public sealed partial class DiffViewerViewModel : ViewModelBase
     [ObservableProperty] private string _displayedDiff = "";
     [ObservableProperty] private string? _statusMessage;
 
+    // ── View toggles (persisted to ui.config.json) ──────────────────────────
+    [ObservableProperty] private bool _isSplitView;
+    [ObservableProperty] private bool _wrapLines;
+
+    partial void OnIsSplitViewChanged(bool value)
+    {
+        _settings.DiffViewMode = value ? "split" : "unified";
+        PersistViewPreferences();
+    }
+
+    partial void OnWrapLinesChanged(bool value)
+    {
+        _settings.DiffWrapLines = value;
+        PersistViewPreferences();
+    }
+
+    /// A failed preference write must never take the diff viewer down with it; the toggle
+    /// still works for this session, it just won't survive a restart.
+    private void PersistViewPreferences()
+    {
+        try { _settings.Save(); }
+        catch (IOException) { }
+        catch (UnauthorizedAccessException) { }
+    }
+
     // ── Planning combined toggle ────────────────────────────────────────────
     [ObservableProperty] private bool _isCombinedMode;
     [ObservableProperty] private string? _combinedWarning;
@@ -63,10 +92,13 @@ public sealed partial class DiffViewerViewModel : ViewModelBase
 
     public Action? CloseAction { get; set; }
 
-    public DiffViewerViewModel(GitService git, IWorkerClient worker)
+    public DiffViewerViewModel(GitService git, IWorkerClient worker, AppSettings settings)
     {
         _git = git;
         _worker = worker;
+        _settings = settings;
+        _isSplitView = string.Equals(settings.DiffViewMode, "split", StringComparison.OrdinalIgnoreCase);
+        _wrapLines = settings.DiffWrapLines;
     }
 
     [RelayCommand]

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

@@ -30,6 +30,12 @@
 
     <DockPanel>
 
+      <!-- View toolbar: layout + wrap, both persisted -->
+      <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Spacing="8" Margin="16,8,16,0">
+        <ToggleButton Content="{loc:Tr modals.diff.splitView}" IsChecked="{Binding IsSplitView}"/>
+        <ToggleButton Content="{loc:Tr modals.diff.wrapLines}" IsChecked="{Binding WrapLines}"/>
+      </StackPanel>
+
       <!-- Planning toolbar: combined-mode toggle + warning/loading -->
       <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Spacing="8" Margin="16,8,16,0"
                   IsVisible="{Binding IsPlanning}">
@@ -149,10 +155,10 @@
                            Foreground="{DynamicResource TextMuteBrush}"
                            IsVisible="{Binding SelectedFile.IsEmptyContent}"
                            HorizontalAlignment="Center" VerticalAlignment="Center"/>
-                <ScrollViewer HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto"
+                <ctl:DiffTextView IsVisible="{Binding SelectedFile.HasLines}"
-                              IsVisible="{Binding SelectedFile.HasLines}">
+                                  File="{Binding SelectedFile}"
-                  <ctl:DiffLinesView Lines="{Binding SelectedFile.Lines}"/>
+                                  IsSplit="{Binding IsSplitView}"
-                </ScrollViewer>
+                                  WrapLines="{Binding WrapLines}"/>
               </Grid>
             </DockPanel>
 

tests/ClaudeDo.Ui.Tests/ViewModels/DiffViewerViewModelTests.cs

@@ -17,6 +17,13 @@ public class DiffViewerViewModelTests
             LocaleStore.Load(Path.Combine(dir!, "src", "ClaudeDo.Localization", "locales")), "en");
     }
 
+    // A throwaway config path — the view toggles call Save(), and a test must never
+    // overwrite the developer's real ~/.todo-app/ui.config.json.
+    private static AppSettings TestSettings() => new()
+    {
+        ConfigPath = Path.Combine(Path.GetTempPath(), $"claudedo-uicfg-{Guid.NewGuid():N}.json"),
+    };
+
     private sealed class FakePlanningWorker : StubWorkerClient
     {
         public IReadOnlyList<SubtaskDiffDto> AggregateResult { get; set; } = Array.Empty<SubtaskDiffDto>();
@@ -36,7 +43,7 @@ public class DiffViewerViewModelTests
     [Fact]
     public async Task CommitRange_NullHeadCommit_ShowsUnavailable()
     {
-        var vm = new DiffViewerViewModel(null!, new FakePlanningWorker());
+        var vm = new DiffViewerViewModel(null!, new FakePlanningWorker(), TestSettings());
         vm.ConfigureCommitRange("/some/repo", "abc123", null);
 
         await vm.LoadAsync();
@@ -49,7 +56,7 @@ public class DiffViewerViewModelTests
     [Fact]
     public async Task CommitRange_NullBaseRef_ShowsUnavailable()
     {
-        var vm = new DiffViewerViewModel(null!, new FakePlanningWorker());
+        var vm = new DiffViewerViewModel(null!, new FakePlanningWorker(), TestSettings());
         vm.ConfigureCommitRange("/some/repo", null, "def456");
 
         await vm.LoadAsync();
@@ -104,7 +111,7 @@ public class DiffViewerViewModelTests
                 new SubtaskDiffDto("s2", "Second", "branch-2", "base2", "head2", "+2 -1", "diff2"),
             }
         };
-        var vm = new DiffViewerViewModel(null!, fake);
+        var vm = new DiffViewerViewModel(null!, fake, TestSettings());
         vm.ConfigurePlanning("plan-1", "main");
 
         await vm.LoadAsync();
@@ -124,7 +131,7 @@ public class DiffViewerViewModelTests
                 new SubtaskDiffDto("s2", "Second", "b2", "base2", "head2", null, "DIFF-B"),
             }
         };
-        var vm = new DiffViewerViewModel(null!, fake);
+        var vm = new DiffViewerViewModel(null!, fake, TestSettings());
         vm.ConfigurePlanning("plan-1", "main");
         await vm.LoadAsync();
 
@@ -141,7 +148,7 @@ public class DiffViewerViewModelTests
             AggregateResult = new[] { new SubtaskDiffDto("s1", "First", "b1", "base1", "head1", null, "DIFF-A") },
             CombinedResult = new CombinedDiffResultDto(true, "integration-branch", "COMBINED-DIFF", null, null),
         };
-        var vm = new DiffViewerViewModel(null!, fake);
+        var vm = new DiffViewerViewModel(null!, fake, TestSettings());
         vm.ConfigurePlanning("plan-1", "main");
         await vm.LoadAsync();
 
@@ -162,7 +169,7 @@ public class DiffViewerViewModelTests
             AggregateResult = new[] { new SubtaskDiffDto("s1", "First", "b1", "base1", "head1", null, "DIFF-A") },
             CombinedResult = new CombinedDiffResultDto(false, null, null, "subtask-42", new[] { "a.cs", "b.cs" }),
         };
-        var vm = new DiffViewerViewModel(null!, fake);
+        var vm = new DiffViewerViewModel(null!, fake, TestSettings());
         vm.ConfigurePlanning("plan-1", "main");
         await vm.LoadAsync();
 
@@ -184,7 +191,7 @@ public class DiffViewerViewModelTests
             AggregateResult = new[] { new SubtaskDiffDto("s1", "First", "b1", "base1", "head1", null, "DIFF-A") },
             CombinedResult = null,
         };
-        var vm = new DiffViewerViewModel(null!, fake);
+        var vm = new DiffViewerViewModel(null!, fake, TestSettings());
         vm.ConfigurePlanning("plan-1", "main");
         await vm.LoadAsync();
 
@@ -205,7 +212,7 @@ public class DiffViewerViewModelTests
             AggregateResult = new[] { new SubtaskDiffDto("s1", "First", "b1", "base1", "head1", null, "DIFF-A") },
             CombinedException = "planning task not found",
         };
-        var vm = new DiffViewerViewModel(null!, fake);
+        var vm = new DiffViewerViewModel(null!, fake, TestSettings());
         vm.ConfigurePlanning("plan-1", "main");
         await vm.LoadAsync();