diff --git a/src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs b/src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs
index 37517f6..c77a924 100644
--- a/src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs
+++ b/src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs
@@ -137,10 +137,12 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase
     // outcomes, each section gated on the relevant state).
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(IsOutputTab))]
+    [NotifyPropertyChangedFor(nameof(IsGitTab))]
     [NotifyPropertyChangedFor(nameof(IsSessionTab))]
     private string _selectedTab = "output";
 
     public bool IsOutputTab  => SelectedTab == "output";
+    public bool IsGitTab     => SelectedTab == "git";
     public bool IsSessionTab => SelectedTab == "session";
 
     [RelayCommand]
diff --git a/tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandTabsTests.cs b/tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandTabsTests.cs
new file mode 100644
index 0000000..e6918e8
--- /dev/null
+++ b/tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandTabsTests.cs
@@ -0,0 +1,83 @@
+using ClaudeDo.Data;
+using ClaudeDo.Ui.Services;
+using ClaudeDo.Ui.ViewModels.Islands;
+using Microsoft.EntityFrameworkCore;
+
+namespace ClaudeDo.Ui.Tests.ViewModels;
+
+public class DetailsIslandTabsTests : IDisposable
+{
+    private readonly string _dbPath;
+
+    public DetailsIslandTabsTests()
+    {
+        _dbPath = Path.Combine(Path.GetTempPath(), $"claudedo_tabs_test_{Guid.NewGuid():N}.db");
+        using var ctx = NewContext();
+        ctx.Database.EnsureCreated();
+    }
+
+    public void Dispose()
+    {
+        try { File.Delete(_dbPath); } catch { }
+        try { File.Delete(_dbPath + "-wal"); } catch { }
+        try { File.Delete(_dbPath + "-shm"); } catch { }
+    }
+
+    private ClaudeDoDbContext NewContext()
+    {
+        var opts = new DbContextOptionsBuilder<ClaudeDoDbContext>()
+            .UseSqlite($"Data Source={_dbPath}")
+            .Options;
+        return new ClaudeDoDbContext(opts);
+    }
+
+    private sealed class TestDbFactory : IDbContextFactory<ClaudeDoDbContext>
+    {
+        private readonly Func<ClaudeDoDbContext> _create;
+        public TestDbFactory(Func<ClaudeDoDbContext> create) => _create = create;
+        public ClaudeDoDbContext CreateDbContext() => _create();
+    }
+
+    private sealed class StubNotesApi : ClaudeDo.Ui.Services.Interfaces.INotesApi
+    {
+        public Task<List<DailyNoteDto>> ListAsync(DateOnly day) => Task.FromResult(new List<DailyNoteDto>());
+        public Task<DailyNoteDto?> AddAsync(DateOnly day, string text) => Task.FromResult<DailyNoteDto?>(null);
+        public Task UpdateAsync(string id, string text) => Task.CompletedTask;
+        public Task DeleteAsync(string id) => Task.CompletedTask;
+    }
+
+    private sealed class NullServiceProvider : IServiceProvider
+    {
+        public object? GetService(Type serviceType) => null;
+    }
+
+    // StubWorkerClient is abstract — use a concrete no-op subclass (same pattern as DetailsIslandPrepModeTests).
+    private sealed class DefaultStub : StubWorkerClient { }
+
+    private DetailsIslandViewModel NewVm()
+    {
+        var factory = new TestDbFactory(NewContext);
+        return new DetailsIslandViewModel(factory, new DefaultStub(), new NullServiceProvider(), new StubNotesApi());
+    }
+
+    [Fact]
+    public void SelectTab_git_sets_IsGitTab_and_clears_others()
+    {
+        var vm = NewVm();
+
+        vm.SelectTabCommand.Execute("git");
+
+        Assert.True(vm.IsGitTab);
+        Assert.False(vm.IsOutputTab);
+        Assert.False(vm.IsSessionTab);
+    }
+
+    [Fact]
+    public void Default_tab_is_output_not_git()
+    {
+        var vm = NewVm();
+
+        Assert.True(vm.IsOutputTab);
+        Assert.False(vm.IsGitTab);
+    }
+}