fix(ui): show a banner when a ConPTY session dies after startup

InteractiveTerminalViewModel.HasExitedAfterStartup now covers every
post-startup death that ExitedAfterStartup alone missed (crash, clean
exit, quiet exit inside the grace window) -- previously the tile just
stayed looking alive/thinking with zero signal. ConPtyPaneView binds a
new banner to it (message + Retry + Close); CanRetry simplifies to
"any HasExited state" since the same descriptor factory can relaunch
either kind of death. HandlerRestartCoordinator's worker-side
auto-restart path is untouched.

src/ClaudeDo.Localization/locales/de.json

@@ -348,6 +348,7 @@
     "closeSession": "Sitzung beenden",
     "conptyLaunchFailed": "Interaktive Sitzung konnte nicht geöffnet werden: {0}",
     "conptyStarting": "Sitzung wird gestartet…",
+    "conptyExited": "Sitzung beendet (Code {0}).",
     "usageWarningNotDelivered": "Die Listen-Handler-Sitzung konnte nicht vor dem Usage-Limit gewarnt werden.",
     "mergeHelperTitle": "Merge-Helfer",
     "mergeHelperHandoffTitleSuffix": " (Übergabe)",

src/ClaudeDo.Localization/locales/en.json

@@ -348,6 +348,7 @@
     "closeSession": "Kill session",
     "conptyLaunchFailed": "Couldn't open interactive session: {0}",
     "conptyStarting": "Starting session…",
+    "conptyExited": "Session ended (code {0}).",
     "usageWarningNotDelivered": "Couldn't warn the list-handler session about the usage limit.",
     "mergeHelperTitle": "Merge Helper",
     "mergeHelperHandoffTitleSuffix": " (Handoff)",

src/ClaudeDo.Ui/ViewModels/InteractiveTerminalViewModel.cs

@@ -36,14 +36,29 @@ public sealed partial class InteractiveTerminalViewModel : ViewModelBase, IDispo
     /// can show a spinner instead of an empty black pane.</summary>
     public bool IsStarting => !IsRunning && !HasExited && StartError is null;
 
+    /// <summary>True once the process has died without a <see cref="StartError"/> already covering it —
+    /// i.e. every death that isn't a launch-time failure: a crash after running a while, a clean exit,
+    /// or a quiet exit inside the startup grace window. Drives the host's "session ended" banner so a
+    /// dead pane never looks like it's still running/thinking.</summary>
+    public bool HasExitedAfterStartup => HasExited && StartError is null;
+
     partial void OnIsRunningChanged(bool value)
     {
         OnPropertyChanged(nameof(IsStarting));
         if (value) _startedAtUtc = _utcNow();
     }
 
-    partial void OnHasExitedChanged(bool value)   => OnPropertyChanged(nameof(IsStarting));
-    partial void OnStartErrorChanged(string? value) => OnPropertyChanged(nameof(IsStarting));
+    partial void OnHasExitedChanged(bool value)
+    {
+        OnPropertyChanged(nameof(IsStarting));
+        OnPropertyChanged(nameof(HasExitedAfterStartup));
+    }
+
+    partial void OnStartErrorChanged(string? value)
+    {
+        OnPropertyChanged(nameof(IsStarting));
+        OnPropertyChanged(nameof(HasExitedAfterStartup));
+    }
 
     public InteractiveTerminalViewModel() : this(() => DateTime.UtcNow)
     {

src/ClaudeDo.Ui/ViewModels/MissionControl/ConPtyPaneViewModel.cs

@@ -2,6 +2,7 @@ using System;
 using System.ComponentModel;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
+using ClaudeDo.Ui.Localization;
 using ClaudeDo.Ui.Services;
 
 namespace ClaudeDo.Ui.ViewModels.MissionControl;
@@ -137,8 +138,18 @@ public sealed partial class ConPtyPaneViewModel : ViewModelBase, IDisposable
             SubmitForReviewCommand.NotifyCanExecuteChanged();
             RetryCommand.NotifyCanExecuteChanged();
         }
+
+        if (e.PropertyName is nameof(InteractiveTerminalViewModel.HasExitedAfterStartup)
+            or nameof(InteractiveTerminalViewModel.ExitCode))
+        {
+            OnPropertyChanged(nameof(ExitedBannerText));
+        }
     }
 
+    /// <summary>"Session ended (code N)" text for <see cref="InteractiveTerminalViewModel.HasExitedAfterStartup"/> —
+    /// computed here (rather than formatted in XAML) since <c>loc:Tr</c> has no binding-arg support.</summary>
+    public string ExitedBannerText => Loc.T("missionControl.conptyExited", Terminal.ExitCode ?? 0);
+
     /// <summary>Types a message into this pane's live session and submits it (the worker's
     /// pre-usage-limit warning). False when the session isn't running.</summary>
     public System.Threading.Tasks.Task<bool> SendLineAsync(string text) => Terminal.SendLineAsync(text);
@@ -167,9 +178,10 @@ public sealed partial class ConPtyPaneViewModel : ViewModelBase, IDisposable
 
     partial void OnIsAbandonPendingChanged(bool value) => AbandonRunCommand.NotifyCanExecuteChanged();
 
-    // A launch failure permanently occupies the TaskId dedupe slot unless the user can retry —
-    // re-opening the same task would otherwise just re-focus a dead tile.
-    private bool CanRetry() => Terminal.HasExited && Terminal.StartError is not null;
+    // A dead session permanently occupies the TaskId dedupe slot unless the user can retry — whether
+    // it died at launch (StartError) or after (HasExitedAfterStartup), the same descriptor factory
+    // can always relaunch it, so any HasExited state is retryable.
+    private bool CanRetry() => Terminal.HasExited;
 
     [RelayCommand(CanExecute = nameof(CanRetry))]
     private void Retry()

src/ClaudeDo.Ui/Views/MissionControl/ConPtyPaneView.axaml

@@ -55,6 +55,27 @@
         </Grid>
       </Border>
 
+      <!-- Session-ended banner: process died without a start-failure already covering it -->
+      <Border DockPanel.Dock="Top"
+              IsVisible="{Binding Terminal.HasExitedAfterStartup}"
+              Background="{DynamicResource ErrorTintBrush}"
+              BorderBrush="{DynamicResource BloodBrush}"
+              BorderThickness="0,0,0,1" Padding="12,6">
+        <Grid ColumnDefinitions="*,Auto,Auto">
+          <TextBlock Grid.Column="0" Classes="meta" Text="{Binding ExitedBannerText}"
+                     Foreground="{DynamicResource BloodBrush}"
+                     TextWrapping="Wrap" VerticalAlignment="Center" />
+          <Button Grid.Column="1" Classes="btn" Margin="12,0,0,0"
+                  Content="{loc:Tr missionControl.retry}"
+                  ToolTip.Tip="{loc:Tr missionControl.retryTip}"
+                  Command="{Binding RetryCommand}" />
+          <Button Grid.Column="2" Classes="btn" Margin="12,0,0,0"
+                  Content="{loc:Tr missionControl.closeSession}"
+                  ToolTip.Tip="{loc:Tr missionControl.closeSession}"
+                  Command="{Binding CloseCommand}" />
+        </Grid>
+      </Border>
+
       <!-- Embedded ConPTY terminal, with a starting overlay until the session is spawned -->
       <Panel>
         <views:InteractiveTerminalView DataContext="{Binding Terminal}" />