feat(ui): confirm main-window close when Mission Control sessions are open

Closing the main window used to silently kill every open Mission Control
ConPTY session (App's ShutdownMode.OnMainWindowClose tears the process down
without warning). Intercept Window.Closing, and when at least one pane is
open, ask via the existing ConfirmAsync pattern before proceeding; cancelling
leaves the window and sessions alive, confirming force-closes as before.

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" },

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" },

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;

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);

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));
+    }
+}