fix(app): stop a dispatcher exception from killing the whole app

Ctrl+C in a Mission Control terminal tile is bound by the terminal library to
CopyAsync, which throws IndexOutOfRangeException out of XTerm's selection buffer
on some selections. It runs from an async void key handler, so the exception
reached the dispatcher unhandled and terminated the process -- every open ConPTY
session with it. Handle it instead and surface the message in the footer error
strip. Iciclecreek.Avalonia.Terminal 2.0.3 is the newest release, so there is no
upstream fix to take.

src/ClaudeDo.App/App.axaml.cs

@@ -3,7 +3,9 @@ using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
+using Avalonia.Threading;
 using ClaudeDo.Ui;
+using ClaudeDo.Ui.Localization;
 using ClaudeDo.Ui.Services;
 using ClaudeDo.Ui.ViewModels;
 using ClaudeDo.Ui.Views;
@@ -40,9 +42,22 @@ public partial class App : Application
             // modeless Mission Control window is still open.
             desktop.ShutdownMode = ShutdownMode.OnMainWindowClose;
 
+            var shell = services.GetRequiredService<IslandsShellViewModel>();
+
+            // Last-resort backstop: an exception escaping a dispatcher job kills the process, and
+            // ClaudeDo hosts third-party UI (the ConPTY terminal control) whose async void key and
+            // render handlers have done exactly that — one bad keystroke took the whole app down,
+            // losing every open session. Swallowing is the lesser evil here: the failing job is
+            // already dead either way, and the user still gets told via the footer error strip.
+            Dispatcher.UIThread.UnhandledException += (_, e) =>
+            {
+                e.Handled = true;
+                shell.FlashFooterError(Loc.T("vm.shell.unexpectedError", e.Exception.Message));
+            };
+
             desktop.MainWindow = new MainWindow
             {
-                DataContext = services.GetRequiredService<IslandsShellViewModel>(),
+                DataContext = shell,
             };
 
             // Kick off the SignalR retry loop — reconnects indefinitely if the worker

src/ClaudeDo.Localization/locales/de.json

@@ -642,7 +642,7 @@
   },
   "vm": {
     "connection": { "online": "Online", "connecting": "Verbinden…", "offline": "Offline" },
-    "shell": { "restartingWorker": "Worker wird neu gestartet…" },
+    "shell": { "restartingWorker": "Worker wird neu gestartet…", "unexpectedError": "Unerwarteter Fehler: {0}" },
     "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" },
     "planningBadge": { "active": "PLANUNG", "finalized": "GEPLANT" },

src/ClaudeDo.Localization/locales/en.json

@@ -642,7 +642,7 @@
   },
   "vm": {
     "connection": { "online": "Online", "connecting": "Connecting…", "offline": "Offline" },
-    "shell": { "restartingWorker": "Restarting worker…" },
+    "shell": { "restartingWorker": "Restarting worker…", "unexpectedError": "Unexpected error: {0}" },
     "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" },
     "planningBadge": { "active": "PLANNING", "finalized": "PLANNED" },