feat(mission-control): Handler-Run per Knopf abbrechen

Ein "Abandon run"-Knopf an Handler-Panes fragt HandlerRoundState.Get(handlerTaskId)
nach den noch offenen (Queued/Running) Tasks des Laufs, bestaetigt mit Anzahl,
cancelt jeden ueber den bestehenden CancelTaskAsync-Pfad und schliesst danach die
Session -- ein Schritt statt Tile schliessen + Queue separat abbrechen. Ohne
offene Tasks (oder ohne Round-Eintrag) schliesst die Aktion direkt, ohne Dialog.
Nur an den beiden Handler-Panes sichtbar (IsListHandler), normale Task-/Ad-hoc-
Panes bleiben unveraendert.

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

@@ -18,6 +18,12 @@ public sealed partial class ConPtyPaneViewModel : ViewModelBase, IDisposable
     // Only a task-based pane can be submitted for review (an ad-hoc directory session has no task).
     public bool IsTaskBased => TaskId is not null;
 
+    /// <summary>Set by the host for a list-handler run ("Let Claude handle it" / "Let Claude merge
+    /// the reviews") pane -- shows the "Abandon run" action. Plain mutable property, not
+    /// <see cref="ObservableProperty"/>: the host sets it once right after construction, before the
+    /// pane is added to the visible collection, so no change notification is needed.</summary>
+    public bool IsListHandler { get; set; }
+
     [ObservableProperty] private string _displayTitle;
 
     [ObservableProperty] private InteractiveTerminalViewModel _terminal = new();
@@ -26,6 +32,10 @@ public sealed partial class ConPtyPaneViewModel : ViewModelBase, IDisposable
     /// flight, so a rapid double-click can't race two submissions for the same task.</summary>
     [ObservableProperty] private bool _isSubmitPending;
 
+    /// <summary>Set by the host while an abandon-run round trip (query open tasks, confirm,
+    /// cancel each, close pane) is in flight, so a rapid double-click can't race two runs.</summary>
+    [ObservableProperty] private bool _isAbandonPending;
+
     /// <summary>Raised when the terminal failed to start — the host surfaces this via the footer error strip.</summary>
     public event Action<string>? ErrorReported;
 
@@ -36,6 +46,12 @@ public sealed partial class ConPtyPaneViewModel : ViewModelBase, IDisposable
     /// commits the worktree and moves the task to WaitingForReview.</summary>
     public event Action<string>? SubmitForReviewRequested;
 
+    /// <summary>Raised when the user abandons a list-handler run (<see cref="IsListHandler"/>
+    /// only): the host looks up this round's still-open tasks, confirms with the user (naming the
+    /// count), cancels them, then closes this pane -- one action instead of closing the tile and
+    /// separately cancelling the queue.</summary>
+    public event Action<string>? AbandonRunRequested;
+
     /// <summary>Raised with <c>(taskId, exitCode)</c> when a task-based session that had been running
     /// dies non-zero. The host reports it to the worker, which decides whether this was a list
     /// handler killed by the usage limit and worth reopening. Ad-hoc panes never raise it — there is
@@ -141,6 +157,16 @@ public sealed partial class ConPtyPaneViewModel : ViewModelBase, IDisposable
 
     partial void OnIsSubmitPendingChanged(bool value) => SubmitForReviewCommand.NotifyCanExecuteChanged();
 
+    private bool CanAbandonRun() => IsListHandler && !IsAbandonPending;
+
+    [RelayCommand(CanExecute = nameof(CanAbandonRun))]
+    private void AbandonRun()
+    {
+        if (TaskId is { } id) AbandonRunRequested?.Invoke(id);
+    }
+
+    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;