diff --git a/src/ClaudeDo.Localization/locales/de.json b/src/ClaudeDo.Localization/locales/de.json
index 4436139a..3031f6bd 100644
--- a/src/ClaudeDo.Localization/locales/de.json
+++ b/src/ClaudeDo.Localization/locales/de.json
@@ -714,6 +714,7 @@
   "vm": {
     "connection": { "online": "Online", "connecting": "Verbinden…", "offline": "Offline" },
     "shell": { "restartingWorker": "Worker wird neu gestartet…", "unexpectedError": "Unerwarteter Fehler: {0}" },
+    "mainWindow": { "closeConfirm": { "message": "{0} Mission-Control-Sitzung(en) laufen noch. Beim Beenden werden sie abgebrochen. Trotzdem schließen?" } },
     "agentStatus": { "idle": "Leerlauf", "queued": "In Warteschlange", "running": "Läuft", "review": "Prüfung", "children": "Wartet auf Teilaufgaben", "done": "Fertig", "failed": "Fehlgeschlagen", "cancelled": "Abgebrochen" },
     "taskStatus": { "idle": "Leerlauf", "queued": "In Warteschlange", "running": "Läuft", "waitingForReview": "Wartet auf Prüfung", "waitingForChildren": "Wartet auf Teilaufgaben", "done": "Fertig", "failed": "Fehlgeschlagen", "cancelled": "Abgebrochen", "parked": "Geparkt", "interactive": "Interaktiv" },
     "failureReason": { "maxTurns": "Turn-Limit erreicht", "timeout": "Zeitüberschreitung", "error": "Fehler", "cancelled": "Abgebrochen", "unknown": "Grund unbekannt" },
diff --git a/src/ClaudeDo.Localization/locales/en.json b/src/ClaudeDo.Localization/locales/en.json
index bbe5aecb..ca29d581 100644
--- a/src/ClaudeDo.Localization/locales/en.json
+++ b/src/ClaudeDo.Localization/locales/en.json
@@ -714,6 +714,7 @@
   "vm": {
     "connection": { "online": "Online", "connecting": "Connecting…", "offline": "Offline" },
     "shell": { "restartingWorker": "Restarting worker…", "unexpectedError": "Unexpected error: {0}" },
+    "mainWindow": { "closeConfirm": { "message": "{0} Mission Control session(s) are still running. Closing the app will end them. Close anyway?" } },
     "agentStatus": { "idle": "Idle", "queued": "Queued", "running": "Running", "review": "Review", "children": "Waiting for Subtasks", "done": "Done", "failed": "Failed", "cancelled": "Cancelled" },
     "taskStatus": { "idle": "Idle", "queued": "Queued", "running": "Running", "waitingForReview": "Waiting for Review", "waitingForChildren": "Waiting for Subtasks", "done": "Done", "failed": "Failed", "cancelled": "Cancelled", "parked": "Parked", "interactive": "Interactive" },
     "failureReason": { "maxTurns": "Turn limit reached", "timeout": "Timed out", "error": "Error", "cancelled": "Cancelled", "unknown": "Unknown reason" },
diff --git a/src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs b/src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs
index 2df99684..aa85bccd 100644
--- a/src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs
+++ b/src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs
@@ -520,6 +520,16 @@ public sealed partial class IslandsShellViewModel : ViewModelBase, IDisposable
             Dialogs.ShowMissionControl(MissionControl);
     }
 
+    /// <summary>Number of Mission Control ConPTY panes currently open — the main window's
+    /// close guard asks for confirmation whenever this is greater than zero.</summary>
+    public int OpenMissionControlSessionCount => MissionControl?.ConPtySessions.Count ?? 0;
+
+    // Pure decision extracted for testability — closing the main window kills every open
+    // Mission Control pane's `claude` process (ConPtyPaneViewModel.Dispose), so ask first
+    // rather than let it happen silently.
+    internal static bool RequiresCloseConfirmation(int openMissionControlSessionCount) =>
+        openMissionControlSessionCount > 0;
+
     private void SyncInteractiveSessionChips()
     {
         if (MissionControl is null || Tasks is null) return;
diff --git a/src/ClaudeDo.Ui/Views/MainWindow.axaml.cs b/src/ClaudeDo.Ui/Views/MainWindow.axaml.cs
index d506f287..b1633f86 100644
--- a/src/ClaudeDo.Ui/Views/MainWindow.axaml.cs
+++ b/src/ClaudeDo.Ui/Views/MainWindow.axaml.cs
@@ -1,9 +1,12 @@
 using System.Linq;
+using System.Threading.Tasks;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Layout;
 using Avalonia.Media;
+using ClaudeDo.Ui.Localization;
+using ClaudeDo.Ui.Services;
 using ClaudeDo.Ui.ViewModels;
 using ClaudeDo.Ui.ViewModels.Islands;
 using ClaudeDo.Ui.ViewModels.Modals;
@@ -13,6 +16,8 @@ namespace ClaudeDo.Ui.Views;
 
 public partial class MainWindow : Window
 {
+    private bool _forceClose;
+
     public MainWindow()
     {
         InitializeComponent();
@@ -21,6 +26,29 @@ public partial class MainWindow : Window
         UpdateMaxIcon();
     }
 
+    // Closing the main window kills every open Mission Control ConPTY session without
+    // warning (App.axaml.cs: ShutdownMode.OnMainWindowClose). Ask first — never silently.
+    protected override void OnClosing(WindowClosingEventArgs e)
+    {
+        if (!_forceClose
+            && DataContext is IslandsShellViewModel { Dialogs: { } dialogs } vm
+            && IslandsShellViewModel.RequiresCloseConfirmation(vm.OpenMissionControlSessionCount))
+        {
+            e.Cancel = true;
+            _ = ConfirmCloseWithOpenSessionsAsync(dialogs, vm.OpenMissionControlSessionCount);
+            return;
+        }
+        base.OnClosing(e);
+    }
+
+    private async Task ConfirmCloseWithOpenSessionsAsync(IDialogService dialogs, int openSessionCount)
+    {
+        var confirmed = await dialogs.ConfirmAsync(Loc.T("vm.mainWindow.closeConfirm.message", openSessionCount));
+        if (!confirmed) return;
+        _forceClose = true;
+        Close();
+    }
+
     protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
     {
         base.OnPropertyChanged(change);
diff --git a/tests/ClaudeDo.Ui.Tests/MainWindowCloseConfirmDecisionTests.cs b/tests/ClaudeDo.Ui.Tests/MainWindowCloseConfirmDecisionTests.cs
new file mode 100644
index 00000000..03d2a729
--- /dev/null
+++ b/tests/ClaudeDo.Ui.Tests/MainWindowCloseConfirmDecisionTests.cs
@@ -0,0 +1,25 @@
+using ClaudeDo.Ui.ViewModels;
+using Xunit;
+
+namespace ClaudeDo.Ui.Tests;
+
+public class MainWindowCloseConfirmDecisionTests
+{
+    [Fact]
+    public void True_when_at_least_one_mission_control_session_is_open()
+    {
+        Assert.True(IslandsShellViewModel.RequiresCloseConfirmation(1));
+    }
+
+    [Fact]
+    public void True_when_multiple_mission_control_sessions_are_open()
+    {
+        Assert.True(IslandsShellViewModel.RequiresCloseConfirmation(3));
+    }
+
+    [Fact]
+    public void False_when_no_mission_control_sessions_are_open()
+    {
+        Assert.False(IslandsShellViewModel.RequiresCloseConfirmation(0));
+    }
+}