diff --git a/src/ClaudeDo.Ui/AppSettings.cs b/src/ClaudeDo.Ui/AppSettings.cs
index 09a82aff..fad7fe9d 100644
--- a/src/ClaudeDo.Ui/AppSettings.cs
+++ b/src/ClaudeDo.Ui/AppSettings.cs
@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using ClaudeDo.Data;
 
 namespace ClaudeDo.Ui;
@@ -10,24 +11,40 @@ public sealed class AppSettings
     public string Language { get; set; } = "";
     public string AccentPreset { get; set; } = "";
 
-    private static readonly string ConfigPath = Paths.Expand("~/.todo-app/ui.config.json");
+    /// Diff viewer layout: "unified" or "split". A view preference, so it lives here in
+    /// ui.config.json rather than in the worker-owned AppSettingsEntity.
+    public string DiffViewMode { get; set; } = "unified";
+    public bool DiffWrapLines { get; set; }
 
-    public static AppSettings Load()
+    private static readonly string DefaultConfigPath = Paths.Expand("~/.todo-app/ui.config.json");
+
+    /// Where this instance persists. Instance-level (not static) so tests can redirect it —
+    /// the diff-viewer toggles call Save() on every flip.
+    [JsonIgnore]
+    public string ConfigPath { get; set; } = DefaultConfigPath;
+
+    public static AppSettings Load(string? configPath = null)
     {
+        var path = configPath ?? DefaultConfigPath;
         try
         {
-            if (File.Exists(ConfigPath))
+            if (File.Exists(path))
             {
-                var json = File.ReadAllText(ConfigPath);
-                return JsonSerializer.Deserialize<AppSettings>(json,
-                    new JsonSerializerOptions { PropertyNameCaseInsensitive = true }) ?? new();
+                var json = File.ReadAllText(path);
+                var loaded = JsonSerializer.Deserialize<AppSettings>(json,
+                    new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
+                if (loaded is not null)
+                {
+                    loaded.ConfigPath = path;
+                    return loaded;
+                }
             }
         }
         catch
         {
             // Fall through to defaults
         }
-        return new();
+        return new AppSettings { ConfigPath = path };
     }
 
     public void Save()
diff --git a/tests/ClaudeDo.Ui.Tests/AppSettingsTests.cs b/tests/ClaudeDo.Ui.Tests/AppSettingsTests.cs
index 88ffdd10..ea22d434 100644
--- a/tests/ClaudeDo.Ui.Tests/AppSettingsTests.cs
+++ b/tests/ClaudeDo.Ui.Tests/AppSettingsTests.cs
@@ -1,22 +1,68 @@
 using System.Text.Json;
 using ClaudeDo.Ui;
+using Xunit;
 
 namespace ClaudeDo.Ui.Tests;
 
 public class AppSettingsTests
 {
+    private static string TempConfigPath() =>
+        Path.Combine(Path.GetTempPath(), $"claudedo-uicfg-{Guid.NewGuid():N}.json");
+
     [Fact]
-    public void Language_defaults_to_empty()
+    public void DiffPreferences_DefaultToUnifiedAndNoWrap()
     {
-        Assert.Equal("", new AppSettings().Language);
+        var settings = new AppSettings();
+
+        Assert.Equal("unified", settings.DiffViewMode);
+        Assert.False(settings.DiffWrapLines);
     }
 
     [Fact]
-    public void Language_round_trips_through_json()
+    public void DiffPreferences_SurviveSaveAndLoad()
     {
-        var json = JsonSerializer.Serialize(new AppSettings { Language = "de" });
-        var back = JsonSerializer.Deserialize<AppSettings>(json,
+        var path = TempConfigPath();
+        try
+        {
+            new AppSettings { ConfigPath = path, DiffViewMode = "split", DiffWrapLines = true }.Save();
+
+            var restored = AppSettings.Load(path);
+
+            Assert.Equal("split", restored.DiffViewMode);
+            Assert.True(restored.DiffWrapLines);
+            Assert.Equal(path, restored.ConfigPath);
+        }
+        finally
+        {
+            if (File.Exists(path)) File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public void ConfigPath_IsNotWrittenIntoTheConfigFile()
+    {
+        var path = TempConfigPath();
+        try
+        {
+            new AppSettings { ConfigPath = path }.Save();
+
+            Assert.DoesNotContain("ConfigPath", File.ReadAllText(path), StringComparison.OrdinalIgnoreCase);
+        }
+        finally
+        {
+            if (File.Exists(path)) File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public void DiffPreferences_ReadFromCamelCasedConfig()
+    {
+        const string json = """{"diffViewMode":"split","diffWrapLines":true}""";
+
+        var restored = JsonSerializer.Deserialize<AppSettings>(json,
             new JsonSerializerOptions { PropertyNameCaseInsensitive = true })!;
-        Assert.Equal("de", back.Language);
+
+        Assert.Equal("split", restored.DiffViewMode);
+        Assert.True(restored.DiffWrapLines);
     }
 }