diff --git a/src/ClaudeDo.Localization/locales/de.json b/src/ClaudeDo.Localization/locales/de.json
index 5aa6b39c..41797703 100644
--- a/src/ClaudeDo.Localization/locales/de.json
+++ b/src/ClaudeDo.Localization/locales/de.json
@@ -358,8 +358,11 @@
       "filesHeader": "Dateien",
       "binary": "Binärdatei — kein Text-Diff",
       "empty": "Kein Inhalt",
+      "unifiedView": "Zusammen",
       "splitView": "Nebeneinander",
-      "wrapLines": "Zeilenumbruch"
+      "wrapLines": "Zeilenumbruch",
+      "paneBase": "BASIS",
+      "paneWorktree": "WORKTREE"
     },
     "worktreesOverview": {
       "refresh": "Aktualisieren",
diff --git a/src/ClaudeDo.Localization/locales/en.json b/src/ClaudeDo.Localization/locales/en.json
index 41213be1..c8f18116 100644
--- a/src/ClaudeDo.Localization/locales/en.json
+++ b/src/ClaudeDo.Localization/locales/en.json
@@ -358,8 +358,11 @@
       "filesHeader": "Files",
       "binary": "Binary file — no text diff",
       "empty": "No content",
+      "unifiedView": "Unified",
       "splitView": "Side by side",
-      "wrapLines": "Wrap lines"
+      "wrapLines": "Wrap lines",
+      "paneBase": "BASE",
+      "paneWorktree": "WORKTREE"
     },
     "worktreesOverview": {
       "refresh": "Refresh",
diff --git a/src/ClaudeDo.Ui/Design/IslandStyles.axaml b/src/ClaudeDo.Ui/Design/IslandStyles.axaml
index 41d37329..c6870765 100644
--- a/src/ClaudeDo.Ui/Design/IslandStyles.axaml
+++ b/src/ClaudeDo.Ui/Design/IslandStyles.axaml
@@ -108,6 +108,9 @@
     <!-- Icon.Settings (gear) -->
     <StreamGeometry x:Key="Icon.Settings">M12 8a4 4 0 1 0 0 8 4 4 0 0 0 0-8z M19.43 12.98c.04-.32.07-.64.07-.98s-.03-.66-.07-.98l2.11-1.65a.5.5 0 0 0 .12-.64l-2-3.46a.5.5 0 0 0-.61-.22l-2.49 1a7.03 7.03 0 0 0-1.69-.98l-.38-2.65a.5.5 0 0 0-.5-.42h-4a.5.5 0 0 0-.5.42l-.38 2.65c-.61.25-1.17.59-1.69.98l-2.49-1a.5.5 0 0 0-.61.22l-2 3.46a.5.5 0 0 0 .12.64l2.11 1.65c-.04.32-.07.65-.07.98s.03.66.07.98l-2.11 1.65a.5.5 0 0 0-.12.64l2 3.46a.5.5 0 0 0 .61.22l2.49-1c.52.4 1.08.73 1.69.98l.38 2.65a.5.5 0 0 0 .5.42h4a.5.5 0 0 0 .5-.42l.38-2.65c.61-.25 1.17-.59 1.69-.98l2.49 1a.5.5 0 0 0 .61-.22l2-3.46a.5.5 0 0 0-.12-.64l-2.11-1.65z</StreamGeometry>
 
+    <!-- Icon.Wrap — a full-width line above a line that wraps back with an arrowhead -->
+    <StreamGeometry x:Key="Icon.Wrap">M3 5 H21 V7 H3 Z M3 11 H17 A4 4 0 0 1 17 19 H12 V21 L7 18 L12 15 V17 H17 A2 2 0 0 0 17 13 H3 Z</StreamGeometry>
+
     <!-- Icon.Skull — filled silhouette: rounded cranium + eye holes (EvenOdd) + jaw -->
     <StreamGeometry x:Key="Icon.Skull">F0 M12 2 C7 2 4 5.5 4 10 C4 13.5 6 16 8 17.5 L8 19 C8 20 8.9 21 10 21 L10 18.5 L14 18.5 L14 21 C15.1 21 16 20 16 19 L16 17.5 C18 16 20 13.5 20 10 C20 5.5 17 2 12 2 Z M8.5 8 L8.5 12 L11 12 L11 8 Z M13 8 L13 12 L15.5 12 L15.5 8 Z</StreamGeometry>
 
@@ -323,8 +326,9 @@
     <Setter Property="BorderBrush" Value="{StaticResource LineBrightBrush}" />
   </Style>
 
-  <!-- Icon button: 24×24 square with hover surface -->
-  <Style Selector="Button.icon-btn">
+  <!-- Icon button: 24×24 square with hover surface. The ToggleButton variant is the same
+       chrome for a persisted on/off control (its "on" state is the :checked rule below). -->
+  <Style Selector="Button.icon-btn, ToggleButton.icon-btn">
     <Setter Property="Width"           Value="24" />
     <Setter Property="Height"          Value="24" />
     <Setter Property="Padding"         Value="0" />
@@ -335,10 +339,53 @@
     <Setter Property="HorizontalContentAlignment" Value="Center" />
     <Setter Property="VerticalContentAlignment"   Value="Center" />
   </Style>
-  <Style Selector="Button.icon-btn:pointerover /template/ ContentPresenter">
+  <Style Selector="Button.icon-btn:pointerover /template/ ContentPresenter, ToggleButton.icon-btn:pointerover /template/ ContentPresenter">
     <Setter Property="Background" Value="{StaticResource Surface2Brush}" />
     <Setter Property="TextElement.Foreground" Value="{StaticResource TextBrush}" />
   </Style>
+  <Style Selector="ToggleButton.icon-btn:checked /template/ ContentPresenter">
+    <Setter Property="Background" Value="{StaticResource Surface3Brush}" />
+    <Setter Property="TextElement.Foreground" Value="{StaticResource AccentBrush}" />
+  </Style>
+  <!-- PathIcon fills with its own Foreground and does not pick up TextElement.Foreground,
+       so the icon's three states are set on the icon itself. -->
+  <Style Selector="ToggleButton.icon-btn PathIcon">
+    <Setter Property="Foreground" Value="{StaticResource TextMuteBrush}" />
+  </Style>
+  <Style Selector="ToggleButton.icon-btn:pointerover PathIcon">
+    <Setter Property="Foreground" Value="{StaticResource TextBrush}" />
+  </Style>
+  <Style Selector="ToggleButton.icon-btn:checked PathIcon">
+    <Setter Property="Foreground" Value="{StaticResource AccentBrush}" />
+  </Style>
+
+  <!-- Segmented switch: one control, mutually exclusive segments, active one highlighted.
+       Use for picking a mode (not for independent on/off flags — those are icon toggles). -->
+  <Style Selector="Border.segmented">
+    <Setter Property="Background"      Value="{StaticResource DeepBrush}" />
+    <Setter Property="BorderBrush"     Value="{StaticResource LineBrush}" />
+    <Setter Property="BorderThickness" Value="1" />
+    <Setter Property="CornerRadius"    Value="{StaticResource ButtonCornerRadius}" />
+    <Setter Property="Padding"         Value="2" />
+  </Style>
+  <Style Selector="Border.segmented Button.segment">
+    <Setter Property="Background"      Value="Transparent" />
+    <Setter Property="BorderThickness" Value="0" />
+    <Setter Property="Padding"         Value="10,4" />
+    <Setter Property="CornerRadius"    Value="4" />
+    <Setter Property="FontFamily"      Value="{StaticResource MonoFont}" />
+    <Setter Property="FontSize"        Value="{StaticResource FontSizeMono}" />
+    <Setter Property="Foreground"      Value="{StaticResource TextMuteBrush}" />
+  </Style>
+  <Style Selector="Border.segmented Button.segment:pointerover /template/ ContentPresenter">
+    <Setter Property="Background"             Value="{StaticResource Surface2Brush}" />
+    <Setter Property="TextElement.Foreground" Value="{StaticResource TextBrush}" />
+  </Style>
+  <!-- Declared after :pointerover so hovering the active segment keeps the active look. -->
+  <Style Selector="Border.segmented Button.segment.active /template/ ContentPresenter">
+    <Setter Property="Background"             Value="{StaticResource Surface3Brush}" />
+    <Setter Property="TextElement.Foreground" Value="{StaticResource AccentBrush}" />
+  </Style>
 
   <!-- Stroke-rendered icon (for line-art geometries that PathIcon would fill away) -->
   <Style Selector="Button.icon-btn Path.plan-icon">
diff --git a/src/ClaudeDo.Ui/ViewModels/Modals/DiffViewerViewModel.cs b/src/ClaudeDo.Ui/ViewModels/Modals/DiffViewerViewModel.cs
index ef11ff9b..070fd8a7 100644
--- a/src/ClaudeDo.Ui/ViewModels/Modals/DiffViewerViewModel.cs
+++ b/src/ClaudeDo.Ui/ViewModels/Modals/DiffViewerViewModel.cs
@@ -65,6 +65,11 @@ public sealed partial class DiffViewerViewModel : ViewModelBase
     [ObservableProperty] private bool _isSplitView;
     [ObservableProperty] private bool _wrapLines;
 
+    // The layout picker is a segmented switch, so each segment sets its own mode rather than
+    // flipping a shared flag — clicking the already-active segment must be a no-op.
+    [RelayCommand] private void ShowUnified() => IsSplitView = false;
+    [RelayCommand] private void ShowSplit() => IsSplitView = true;
+
     partial void OnIsSplitViewChanged(bool value)
     {
         _settings.DiffViewMode = value ? "split" : "unified";
diff --git a/src/ClaudeDo.Ui/Views/Conflicts/ConflictResolverView.axaml.cs b/src/ClaudeDo.Ui/Views/Conflicts/ConflictResolverView.axaml.cs
index 2e337146..47f57c50 100644
--- a/src/ClaudeDo.Ui/Views/Conflicts/ConflictResolverView.axaml.cs
+++ b/src/ClaudeDo.Ui/Views/Conflicts/ConflictResolverView.axaml.cs
@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
-using System.IO;
 using System.Linq;
 using System.Text;
 using Avalonia;
@@ -9,22 +8,21 @@ using Avalonia.Controls;
 using Avalonia.Controls.Shapes;
 using Avalonia.Media;
 using Avalonia.Threading;
-using Avalonia.VisualTree;
-using AvaloniaEdit;
 using AvaloniaEdit.Document;
 using AvaloniaEdit.Editing;
 using AvaloniaEdit.Rendering;
 using AvaloniaEdit.TextMate;
 using ClaudeDo.Ui.ViewModels.Conflicts;
-using TextMateSharp.Grammars;
+using ClaudeDo.Ui.Views.Controls;
+using Seg = ClaudeDo.Ui.Views.Controls.DiffEditorSetup.Seg;
 
 namespace ClaudeDo.Ui.Views.Conflicts;
 
 public partial class ConflictResolverView : Window
 {
     private ConflictResolverViewModel? _vm;
-    private RegistryOptions? _registry;
     private TextMate.Installation? _oursTm, _resultTm, _theirsTm;
+    private bool _editorsReady;
 
     // Fixed conflict spans for the read-only side panes (recomputed each rebuild).
     private List<(int Offset, int Length, MergeConflictBlock Block)> _oursSpans = new();
@@ -34,11 +32,8 @@ public partial class ConflictResolverView : Window
     private readonly List<ResultRegion> _resultRegions = new();
     private readonly List<MergeConflictBlock> _hookedBlocks = new();
 
-    private ScrollViewer?[] _scrollViewers = Array.Empty<ScrollViewer?>();
-    private bool _wired;
     private bool _rebuilding;
     private bool _applyingAccept;
-    private bool _syncing;
     private bool _gutterPending;
     private int _gutterRetries;
 
@@ -56,12 +51,6 @@ public partial class ConflictResolverView : Window
             _vm.ActiveFileChanged -= Rebuild;
             _vm.CurrentChanged -= ScrollToCurrent;
         }
-        // The editors persist across a DataContext swap, so drop stale scroll-sync hooks first.
-        foreach (var sv in _scrollViewers)
-            if (sv is not null) sv.ScrollChanged -= OnPaneScroll;
-        _scrollViewers = Array.Empty<ScrollViewer?>();
-        _wired = false;
-
         _vm = DataContext as ConflictResolverViewModel;
         if (_vm is null) return;
 
@@ -76,19 +65,24 @@ public partial class ConflictResolverView : Window
 
     private void EnsureEditors()
     {
-        if (_registry is not null) return;
-        _registry = new RegistryOptions(ThemeName.DarkPlus);
-        _oursTm   = OursEditor.InstallTextMate(_registry);
-        _resultTm = ResultEditor.InstallTextMate(_registry);
-        _theirsTm = TheirsEditor.InstallTextMate(_registry);
+        if (_editorsReady) return;
+        _editorsReady = true;
+        _oursTm   = DiffEditorSetup.InstallHighlighting(OursEditor);
+        _resultTm = DiffEditorSetup.InstallHighlighting(ResultEditor);
+        _theirsTm = DiffEditorSetup.InstallHighlighting(TheirsEditor);
 
         ResultEditor.Document ??= new TextDocument();
         ResultEditor.Document.Changed += OnResultDocumentChanged;
         ResultEditor.TextArea.ReadOnlySectionProvider =
             new ConflictReadOnlyProvider(() => _resultRegions.Select(r => (r.Start.Offset, r.End.Offset)));
 
-        var conflict = BrushRes("MergeConflictTintBrush", Color.Parse("#28C87060"));
-        var resolved = BrushRes("MergeResolvedTintBrush", Color.Parse("#206FA86B"));
+        // Panes are whole files here, not aligned rows, so raw pixel offsets line up and the
+        // gutter buttons only have to be repositioned once per scroll.
+        new VerticalScrollSync(new[] { OursEditor, ResultEditor, TheirsEditor },
+                               afterSync: PositionGutters);
+
+        var conflict = DiffEditorSetup.Brush(this, "MergeConflictTintBrush", Color.Parse("#28C87060"));
+        var resolved = DiffEditorSetup.Brush(this, "MergeResolvedTintBrush", Color.Parse("#206FA86B"));
         OursEditor.TextArea.TextView.BackgroundRenderers.Add(new MergeBlockRenderer(
             () => _oursSpans.Select(s => (s.Offset, s.Length, s.Block.IsResolved)), conflict, resolved));
         ResultEditor.TextArea.TextView.BackgroundRenderers.Add(new MergeBlockRenderer(
@@ -97,13 +91,6 @@ public partial class ConflictResolverView : Window
             () => _theirsSpans.Select(s => (s.Offset, s.Length, s.Block.IsResolved)), conflict, resolved));
     }
 
-    private IBrush BrushRes(string key, Color fallback)
-    {
-        if (this.TryGetResource(key, null, out var v) && v is IBrush b)
-            return b;
-        return new SolidColorBrush(fallback);
-    }
-
     // ── Rebuild the three documents for the active file ───────────────────────
 
     private void Rebuild()
@@ -151,16 +138,11 @@ public partial class ConflictResolverView : Window
                 _hookedBlocks.Add(block);
             }
 
-            ApplyGrammar(file.Path);
+            DiffEditorSetup.ApplyGrammar(file.Path, _oursTm, _resultTm, _theirsTm);
             InvalidateRenderers();
         }
         finally { _rebuilding = false; }
 
-        if (!_wired)
-        {
-            _wired = true;
-            Dispatcher.UIThread.Post(HookScrollSync, DispatcherPriority.Loaded);
-        }
         QueueGutters();
     }
 
@@ -317,8 +299,8 @@ public partial class ConflictResolverView : Window
         if (h <= 1) return;
         var doc = ResultEditor.Document;
         var totalLines = Math.Max(1, doc.LineCount);
-        var unresolved = BrushRes("MergeConflictEdgeBrush", Color.Parse("#80C87060"));
-        var resolved = BrushRes("MergeResolvedEdgeBrush", Color.Parse("#806FA86B"));
+        var unresolved = DiffEditorSetup.Brush(this, "MergeConflictEdgeBrush", Color.Parse("#80C87060"));
+        var resolved = DiffEditorSetup.Brush(this, "MergeResolvedEdgeBrush", Color.Parse("#806FA86B"));
 
         foreach (var region in _resultRegions)
         {
@@ -348,31 +330,6 @@ public partial class ConflictResolverView : Window
 
     private static string Tr(string key) => ClaudeDo.Ui.Localization.Loc.T(key);
 
-    // ── Synced vertical scroll across the three panes ─────────────────────────
-
-    private void HookScrollSync()
-    {
-        _scrollViewers = new[] { OursEditor, ResultEditor, TheirsEditor }
-            .Select(ed => ed.FindDescendantOfType<ScrollViewer>())
-            .ToArray();
-        foreach (var sv in _scrollViewers)
-            if (sv is not null) sv.ScrollChanged += OnPaneScroll;
-    }
-
-    private void OnPaneScroll(object? sender, ScrollChangedEventArgs e)
-    {
-        if (_syncing || sender is not ScrollViewer src) return;
-        _syncing = true;
-        try
-        {
-            foreach (var sv in _scrollViewers)
-                if (sv is not null && !ReferenceEquals(sv, src) && Math.Abs(sv.Offset.Y - src.Offset.Y) > 0.5)
-                    sv.Offset = new Vector(sv.Offset.X, src.Offset.Y);
-        }
-        finally { _syncing = false; }
-        PositionGutters();
-    }
-
     private void ScrollToCurrent()
     {
         if (_vm?.Current is not { } block) return;
@@ -390,30 +347,8 @@ public partial class ConflictResolverView : Window
         TheirsEditor.TextArea.TextView.InvalidateVisual();
     }
 
-    private void ApplyGrammar(string? path)
-    {
-        if (_registry is null || string.IsNullOrEmpty(path)) return;
-        var ext = System.IO.Path.GetExtension(path);
-        if (string.IsNullOrEmpty(ext)) return;
-        var language = _registry.GetLanguageByExtension(ext);
-        if (language is null) return;
-        var scope = _registry.GetScopeByLanguageId(language.Id);
-        _oursTm?.SetGrammar(scope);
-        _resultTm?.SetGrammar(scope);
-        _theirsTm?.SetGrammar(scope);
-    }
-
     // ── Helper types (single-consumer; live with their consumer per repo style) ─
 
-    /// <summary>A minimal <see cref="ISegment"/> for geometry/read-only queries.</summary>
-    private readonly struct Seg : ISegment
-    {
-        public Seg(int offset, int length) { Offset = offset; Length = length; }
-        public int Offset { get; }
-        public int Length { get; }
-        public int EndOffset => Offset + Length;
-    }
-
     /// <summary>An editable conflict region in the result document, tracking which sides are
     /// currently included (in click order — <c>'o'</c> = ours/main, <c>'t'</c> = theirs/incoming).</summary>
     private sealed class ResultRegion
diff --git a/src/ClaudeDo.Ui/Views/Controls/DiffEditorSetup.cs b/src/ClaudeDo.Ui/Views/Controls/DiffEditorSetup.cs
new file mode 100644
index 00000000..d562cf99
--- /dev/null
+++ b/src/ClaudeDo.Ui/Views/Controls/DiffEditorSetup.cs
@@ -0,0 +1,170 @@
+using System;
+using System.IO;
+using System.Linq;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Media;
+using Avalonia.VisualTree;
+using AvaloniaEdit;
+using AvaloniaEdit.Document;
+using AvaloniaEdit.Rendering;
+using AvaloniaEdit.TextMate;
+using TextMateSharp.Grammars;
+
+namespace ClaudeDo.Ui.Views.Controls;
+
+/// <summary>
+/// The AvaloniaEdit host plumbing shared by the two diff surfaces: the read-only side-by-side
+/// <see cref="DiffTextView"/> and the 3-pane conflict resolver.
+/// </summary>
+/// <remarks>
+/// Only the boilerplate lives here. The two surfaces are not variants of one control — one is a
+/// read-only two-way renderer over aligned diff rows (with filler rows the other has no concept
+/// of), the other a three-way editor over a writable result document with anchored regions. Their
+/// documents, margins and background renderers therefore stay with their own views.
+/// </remarks>
+internal static class DiffEditorSetup
+{
+    /// Grammars and themes are process-wide; loading a registry per view would be wasteful.
+    public static readonly RegistryOptions Registry = new(ThemeName.DarkPlus);
+
+    public static TextMate.Installation InstallHighlighting(TextEditor editor) =>
+        editor.InstallTextMate(Registry);
+
+    /// <summary>
+    /// Points every installation at the grammar for <paramref name="path"/>'s extension. No path,
+    /// no extension or no matching language leaves the editors as plain text.
+    /// </summary>
+    /// <remarks>
+    /// Both surfaces feed fragments (diff hunks / conflict regions) rather than whole files, so
+    /// TextMate's line-by-line state can be wrong at a fragment boundary — a line inside a block
+    /// comment may highlight as code. Accepted; every fragment-based diff viewer has this.
+    /// </remarks>
+    public static void ApplyGrammar(string? path, params TextMate.Installation?[] installations)
+    {
+        if (string.IsNullOrEmpty(path)) return;
+        var ext = Path.GetExtension(path);
+        if (string.IsNullOrEmpty(ext)) return;
+        var language = Registry.GetLanguageByExtension(ext);
+        if (language is null) return;
+        var scope = Registry.GetScopeByLanguageId(language.Id);
+        foreach (var installation in installations) installation?.SetGrammar(scope);
+    }
+
+    /// <summary>Resolves a themed brush, falling back to a literal when the lookup fails.</summary>
+    /// <remarks>
+    /// Two traps, both silent. It must be <c>TryFindResource</c> (the extension that walks up to
+    /// Application) and not the <c>TryGetResource</c> instance method, which only sees the
+    /// control's own Resources. And it must run while <paramref name="owner"/> is attached —
+    /// a detached control has no resource parent to walk, so resolving in a constructor freezes
+    /// every brush on its fallback for good.
+    /// </remarks>
+    public static IBrush Brush(Control owner, string key, Color fallback) =>
+        owner.TryFindResource(key, out var value) && value is IBrush brush
+            ? brush
+            : new SolidColorBrush(fallback);
+
+    /// <summary>A minimal <see cref="ISegment"/> for geometry and read-only queries.</summary>
+    public readonly struct Seg : ISegment
+    {
+        public Seg(int offset, int length) { Offset = offset; Length = length; }
+        public int Offset { get; }
+        public int Length { get; }
+        public int EndOffset => Offset + Length;
+    }
+}
+
+/// <summary>
+/// Keeps a set of editors scrolled to the same vertical position. Construction wires the panes;
+/// there is nothing to dispose, and nothing to keep a reference to — the event subscriptions on
+/// the text views own the instance.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Reading is driven off <see cref="TextView.ScrollOffsetChanged"/> rather than the editors'
+/// templated ScrollViewers. A TextView exists from construction, whereas the ScrollViewer only
+/// materialises once the editor has been measured — so subscribing to the ScrollViewer at load
+/// time found nothing whenever a pane started out collapsed, and the sync then stayed dead for
+/// the lifetime of the window.
+/// </para>
+/// <para>
+/// Writing still goes through the ScrollViewer, resolved lazily on first use (by which point the
+/// panes are on screen). <see cref="TextEditor.ScrollToVerticalOffset"/> looks like the obvious
+/// call and is <b>silently a no-op</b> in AvaloniaEdit 12 even with the editor templated and
+/// <c>TextEditor.ScrollViewer</c> non-null — verified against 12.0.0. Assigning
+/// <c>ILogicalScrollable.Offset</c> on the TextView is no good either: it moves the text but
+/// leaves the ScrollViewer's own offset (and therefore the scrollbar thumb) behind.
+/// </para>
+/// </remarks>
+internal sealed class VerticalScrollSync
+{
+    private readonly TextEditor[] _editors;
+    private readonly ScrollViewer?[] _viewers;
+    private readonly Func<bool> _isActive;
+    private readonly Func<bool> _anchorByLine;
+    private readonly Action? _afterSync;
+    private bool _syncing;
+
+    /// <param name="isActive">Gate for layouts where the panes are not side by side.</param>
+    /// <param name="anchorByLine">True while lines wrap — see <see cref="TargetOffset"/>.</param>
+    /// <param name="afterSync">Runs once per user scroll, not per echo.</param>
+    public VerticalScrollSync(TextEditor[] editors, Func<bool>? isActive = null,
+                              Func<bool>? anchorByLine = null, Action? afterSync = null)
+    {
+        _editors = editors;
+        _viewers = new ScrollViewer?[editors.Length];
+        _isActive = isActive ?? (() => true);
+        _anchorByLine = anchorByLine ?? (() => false);
+        _afterSync = afterSync;
+
+        for (var i = 0; i < editors.Length; i++)
+        {
+            var index = i;
+            editors[i].TextArea.TextView.ScrollOffsetChanged += (_, _) => Sync(index);
+        }
+    }
+
+    /// Resolved on demand and cached: at construction the editor may still be collapsed and
+    /// therefore untemplated, but by the time anything scrolls it is on screen.
+    private ScrollViewer? Viewer(int index) =>
+        _viewers[index] ??= _editors[index].GetVisualDescendants().OfType<ScrollViewer>().FirstOrDefault();
+
+    private void Sync(int sourceIndex)
+    {
+        if (_syncing || !_isActive()) return;
+
+        _syncing = true;
+        try
+        {
+            for (var i = 0; i < _editors.Length; i++)
+            {
+                if (i == sourceIndex) continue;
+                if (Viewer(i) is not { } viewer) continue;
+                if (TargetOffset(_editors[sourceIndex], _editors[i]) is not { } y) continue;
+                // The echo from the target's own ScrollOffsetChanged lands after _syncing is
+                // cleared again, so this comparison — not the flag — is what ends the loop.
+                if (Math.Abs(viewer.Offset.Y - y) > 0.5)
+                    viewer.Offset = new Vector(viewer.Offset.X, y);
+            }
+        }
+        finally { _syncing = false; }
+
+        _afterSync?.Invoke();
+    }
+
+    /// Where <paramref name="target"/> has to sit to show the same content as
+    /// <paramref name="source"/>, or null when the two cannot be related right now.
+    private double? TargetOffset(TextEditor source, TextEditor target)
+    {
+        if (!_anchorByLine()) return source.TextArea.TextView.ScrollOffset.Y;
+
+        // Line heights differ once lines wrap, so pixel offsets no longer correspond between the
+        // panes — anchor on the top visible line instead and top-align it by computing the
+        // target's own vertical offset for that document line. ScrollToLine would not do: it is a
+        // "bring into view" primitive that parks the line near mid-viewport past a threshold.
+        if (source.TextArea.TextView.VisualLines is not { Count: > 0 } visualLines) return null;
+        var line = visualLines[0].FirstDocumentLine.LineNumber;
+        if (line < 1 || line > target.Document.LineCount) return null;
+        return target.TextArea.TextView.GetVisualTopByDocumentLine(line);
+    }
+}
diff --git a/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml b/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml
index 425f9860..baba4247 100644
--- a/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml
+++ b/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml
@@ -1,6 +1,7 @@
 <UserControl xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:ae="using:AvaloniaEdit"
+             xmlns:loc="using:ClaudeDo.Ui.Localization"
              x:Class="ClaudeDo.Ui.Views.Controls.DiffTextView">
 
   <UserControl.Styles>
@@ -12,9 +13,23 @@
     </Style>
   </UserControl.Styles>
 
-  <Grid x:Name="PaneGrid" ColumnDefinitions="*,1,*">
-    <ae:TextEditor Grid.Column="0" x:Name="LeftEditor"  IsReadOnly="True" ShowLineNumbers="False"/>
-    <Border        Grid.Column="1" x:Name="PaneDivider" Background="{DynamicResource LineBrush}"/>
-    <ae:TextEditor Grid.Column="2" x:Name="RightEditor" IsReadOnly="True" ShowLineNumbers="False"/>
-  </Grid>
+  <DockPanel>
+    <!-- Split-only: labels which side is which. Same column definitions as the pane grid
+         so each label sits over its own editor. Hidden in unified layout (see RefreshLayout). -->
+    <Grid x:Name="PaneHeader" DockPanel.Dock="Top" ColumnDefinitions="*,1,*" IsVisible="False">
+      <Border Grid.Column="0" Classes="island-header">
+        <TextBlock Classes="eyebrow" Text="{loc:Tr modals.diff.paneBase}"/>
+      </Border>
+      <Border Grid.Column="1" Background="{DynamicResource LineBrush}"/>
+      <Border Grid.Column="2" Classes="island-header">
+        <TextBlock Classes="eyebrow" Text="{loc:Tr modals.diff.paneWorktree}"/>
+      </Border>
+    </Grid>
+
+    <Grid x:Name="PaneGrid" ColumnDefinitions="*,1,*">
+      <ae:TextEditor Grid.Column="0" x:Name="LeftEditor"  IsReadOnly="True" ShowLineNumbers="False"/>
+      <Border        Grid.Column="1" x:Name="PaneDivider" Background="{DynamicResource LineBrush}"/>
+      <ae:TextEditor Grid.Column="2" x:Name="RightEditor" IsReadOnly="True" ShowLineNumbers="False"/>
+    </Grid>
+  </DockPanel>
 </UserControl>
diff --git a/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml.cs b/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml.cs
index 21838697..b6670ebc 100644
--- a/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml.cs
+++ b/src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml.cs
@@ -1,19 +1,14 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
-using System.IO;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Media;
-using Avalonia.Threading;
-using Avalonia.VisualTree;
-using AvaloniaEdit;
-using AvaloniaEdit.Document;
 using AvaloniaEdit.Editing;
 using AvaloniaEdit.Rendering;
 using AvaloniaEdit.TextMate;
 using ClaudeDo.Ui.ViewModels.Modals;
-using TextMateSharp.Grammars;
+using Seg = ClaudeDo.Ui.Views.Controls.DiffEditorSetup.Seg;
 
 namespace ClaudeDo.Ui.Views.Controls;
 
@@ -52,9 +47,6 @@ public partial class DiffTextView : UserControl
         set => SetValue(WrapLinesProperty, value);
     }
 
-    // Grammars and themes are process-wide; loading the registry per control would be wasteful.
-    private static readonly RegistryOptions Registry = new(ThemeName.DarkPlus);
-
     private TextMate.Installation? _leftTm, _rightTm;
 
     // Row lookup per editor, indexed by document line number (1-based). Populated on rebuild
@@ -66,18 +58,16 @@ public partial class DiffTextView : UserControl
 
     private DiffLineNumberMargin? _leftMargin, _rightMargin;
 
-    private ScrollViewer? _leftScroll, _rightScroll;
-    private bool _scrollHooked;
-    private bool _syncing;
     private bool _renderersInstalled;
 
     public DiffTextView()
     {
         InitializeComponent();
-        _leftTm = LeftEditor.InstallTextMate(Registry);
-        _rightTm = RightEditor.InstallTextMate(Registry);
+        _leftTm = DiffEditorSetup.InstallHighlighting(LeftEditor);
+        _rightTm = DiffEditorSetup.InstallHighlighting(RightEditor);
         ReloadFile();
-        HookScrollSync();
+        new VerticalScrollSync(new[] { LeftEditor, RightEditor },
+                               isActive: () => IsSplit, anchorByLine: () => WrapLines);
     }
 
     /// Brushes and the mono typeface only resolve once the control is in the visual tree —
@@ -121,6 +111,7 @@ public partial class DiffTextView : UserControl
         var split = IsSplit;
         RightEditor.IsVisible = split;
         PaneDivider.IsVisible = split;
+        PaneHeader.IsVisible = split;
         Grid.SetColumnSpan(LeftEditor, split ? 1 : 3);
 
         if (split)
@@ -146,7 +137,7 @@ public partial class DiffTextView : UserControl
 
         RebuildMargins();
         ApplyWrap();
-        ApplyGrammar(File?.Path);
+        DiffEditorSetup.ApplyGrammar(File?.Path, _leftTm, _rightTm);
         InvalidateRenderers();
     }
 
@@ -171,21 +162,6 @@ public partial class DiffTextView : UserControl
         RightEditor.WordWrap = WrapLines;
     }
 
-    /// Only hunks are in the document, not whole files, so TextMate's line-by-line state can
-    /// be wrong at a fragment boundary (a line inside a block comment may highlight as code).
-    /// Accepted — every fragment-based diff viewer has this.
-    private void ApplyGrammar(string? path)
-    {
-        if (string.IsNullOrEmpty(path)) return;
-        var ext = Path.GetExtension(path);
-        if (string.IsNullOrEmpty(ext)) return;
-        var language = Registry.GetLanguageByExtension(ext);
-        if (language is null) return;
-        var scope = Registry.GetScopeByLanguageId(language.Id);
-        _leftTm?.SetGrammar(scope);
-        _rightTm?.SetGrammar(scope);
-    }
-
     /// The margin's column layout depends on split vs unified, so it is rebuilt rather than
     /// reconfigured whenever the layout changes.
     private void RebuildMargins()
@@ -205,10 +181,7 @@ public partial class DiffTextView : UserControl
         RightEditor.TextArea.LeftMargins.Insert(0, _rightMargin);
     }
 
-    private IBrush Brush(string key, Color fallback) =>
-        this.TryFindResource(key, out var value) && value is IBrush brush
-            ? brush
-            : new SolidColorBrush(fallback);
+    private IBrush Brush(string key, Color fallback) => DiffEditorSetup.Brush(this, key, fallback);
 
     private void InstallRenderers()
     {
@@ -231,58 +204,6 @@ public partial class DiffTextView : UserControl
         RightEditor.TextArea.TextView.InvalidateVisual();
     }
 
-    /// The editors' ScrollViewers only exist once the template has been applied.
-    private void HookScrollSync()
-    {
-        if (_scrollHooked) return;
-        _scrollHooked = true;
-        Dispatcher.UIThread.Post(() =>
-        {
-            _leftScroll = LeftEditor.FindDescendantOfType<ScrollViewer>();
-            _rightScroll = RightEditor.FindDescendantOfType<ScrollViewer>();
-            if (_leftScroll is not null) _leftScroll.ScrollChanged += OnPaneScroll;
-            if (_rightScroll is not null) _rightScroll.ScrollChanged += OnPaneScroll;
-        }, DispatcherPriority.Loaded);
-    }
-
-    private void OnPaneScroll(object? sender, ScrollChangedEventArgs e)
-    {
-        if (_syncing || !IsSplit || _leftScroll is null || _rightScroll is null) return;
-        var fromLeft = ReferenceEquals(sender, _leftScroll);
-        var source = fromLeft ? _leftScroll : _rightScroll;
-        var target = fromLeft ? _rightScroll : _leftScroll;
-        var targetEditor = fromLeft ? RightEditor : LeftEditor;
-        var sourceEditor = fromLeft ? LeftEditor : RightEditor;
-
-        _syncing = true;
-        try
-        {
-            if (WrapLines)
-            {
-                // Line heights differ once lines wrap, so anchor on the top visible line.
-                // ScrollToLine/ScrollTo are "bring into view" primitives (they park the line
-                // near mid-viewport past a hysteresis threshold) — top-align by computing the
-                // target's own vertical offset for that document line and assigning it
-                // directly, the same way the non-wrap branch assigns Offset below. That is
-                // synchronous, so the same offset-comparison guard makes the echo self-terminate.
-                var topLine = sourceEditor.TextArea.TextView.VisualLines is { Count: > 0 } visualLines
-                    ? visualLines[0].FirstDocumentLine.LineNumber
-                    : (int?)null;
-                if (topLine is { } line && line >= 1 && line <= targetEditor.Document.LineCount)
-                {
-                    var targetTop = targetEditor.TextArea.TextView.GetVisualTopByDocumentLine(line);
-                    if (Math.Abs(target.Offset.Y - targetTop) > 0.5)
-                        target.Offset = new Vector(target.Offset.X, targetTop);
-                }
-            }
-            else if (Math.Abs(target.Offset.Y - source.Offset.Y) > 0.5)
-            {
-                target.Offset = new Vector(target.Offset.X, source.Offset.Y);
-            }
-        }
-        finally { _syncing = false; }
-    }
-
     /// <summary>What one document line represents, for the margin and the background renderers.</summary>
     internal sealed record RowInfo(
         AlignedSide Kind, int? OldNo, int? NewNo, IReadOnlyList<TextSpan> Spans);
@@ -428,13 +349,4 @@ public partial class DiffTextView : UserControl
             }
         }
     }
-
-    /// <summary>A minimal <see cref="ISegment"/> for geometry queries.</summary>
-    private readonly struct Seg : ISegment
-    {
-        public Seg(int offset, int length) { Offset = offset; Length = length; }
-        public int Offset { get; }
-        public int Length { get; }
-        public int EndOffset => Offset + Length;
-    }
 }
diff --git a/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml b/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml
index 003cdaf2..89fbd4e1 100644
--- a/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml
+++ b/src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml
@@ -30,10 +30,24 @@
 
     <DockPanel>
 
-      <!-- View toolbar: layout + wrap, both persisted -->
+      <!-- View toolbar: layout mode (segmented) + wrap (icon toggle), both persisted.
+           Wrap is orthogonal to the layout mode, so it stays a separate control. -->
       <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}"/>
+        <Border Classes="segmented">
+          <StackPanel Orientation="Horizontal">
+            <Button Classes="segment" Classes.active="{Binding !IsSplitView}"
+                    Content="{loc:Tr modals.diff.unifiedView}"
+                    Command="{Binding ShowUnifiedCommand}"/>
+            <Button Classes="segment" Classes.active="{Binding IsSplitView}"
+                    Content="{loc:Tr modals.diff.splitView}"
+                    Command="{Binding ShowSplitCommand}"/>
+          </StackPanel>
+        </Border>
+        <ToggleButton Classes="icon-btn" IsChecked="{Binding WrapLines}"
+                      VerticalAlignment="Center"
+                      ToolTip.Tip="{loc:Tr modals.diff.wrapLines}">
+          <PathIcon Data="{StaticResource Icon.Wrap}" Width="14" Height="14"/>
+        </ToggleButton>
       </StackPanel>
 
       <!-- Planning toolbar: combined-mode toggle + warning/loading -->