diff --git a/src/ClaudeDo.Ui/ViewModels/Islands/TasksIslandViewModel.cs b/src/ClaudeDo.Ui/ViewModels/Islands/TasksIslandViewModel.cs
index 198bd032..2d86ce68 100644
--- a/src/ClaudeDo.Ui/ViewModels/Islands/TasksIslandViewModel.cs
+++ b/src/ClaudeDo.Ui/ViewModels/Islands/TasksIslandViewModel.cs
@@ -1298,6 +1298,10 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
         if (ReconcileTickTestBarrier is { } barrier) await barrier();
 
         var byId = entities.ToDictionary(e => e.Id);
+        // Index the rows once instead of scanning Items per id — at the 500-row cap a linear
+        // scan per id is 250k comparisons every few seconds, for nothing.
+        var rowById = new Dictionary<string, TaskRowViewModel>(Items.Count);
+        foreach (var r in Items) rowById[r.Id] = r;
         foreach (var id in ids)
         {
             // Superseded by a fresher delta refresh or a later tick that landed while this one
@@ -1305,8 +1309,7 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
             if (!_deltaSeq.TryGetValue(id, out var current) || current != seqByTaskId[id]) continue;
             if (!byId.TryGetValue(id, out var entity)) continue; // deleted; the delta path removes rows, not the tick
 
-            var row = Items.FirstOrDefault(r => r.Id == id);
-            row?.UpdateFromEntity(entity);
+            if (rowById.TryGetValue(id, out var row)) row.UpdateFromEntity(entity);
         }
     }
 }
diff --git a/src/ClaudeDo.Ui/ViewModels/Modals/LogVisualizerViewModel.cs b/src/ClaudeDo.Ui/ViewModels/Modals/LogVisualizerViewModel.cs
index 9b4a8a27..b775b323 100644
--- a/src/ClaudeDo.Ui/ViewModels/Modals/LogVisualizerViewModel.cs
+++ b/src/ClaudeDo.Ui/ViewModels/Modals/LogVisualizerViewModel.cs
@@ -75,10 +75,18 @@ public sealed partial class LogVisualizerViewModel : ViewModelBase
 
     [RelayCommand]
     private void Close()
+    {
+        StopReconcileTick();
+        CloseAction?.Invoke();
+    }
+
+    /// <summary>Stops the reconcile tick. Also called from the dialog's native-close fallback
+    /// (WindowDialogService), which bypasses <see cref="CloseCommand"/> — otherwise an Alt+F4
+    /// leaves the timer polling the worker on an orphaned VM. Idempotent.</summary>
+    internal void StopReconcileTick()
     {
         _reconcileTimer.Stop();
         _reconcileTimer.Dispose();
-        CloseAction?.Invoke();
     }
 
     private bool CanCopyLast() => Rows.Count > 0;
diff --git a/src/ClaudeDo.Ui/ViewModels/Modals/WorktreesOverviewModalViewModel.cs b/src/ClaudeDo.Ui/ViewModels/Modals/WorktreesOverviewModalViewModel.cs
index 8bce9961..1c839acb 100644
--- a/src/ClaudeDo.Ui/ViewModels/Modals/WorktreesOverviewModalViewModel.cs
+++ b/src/ClaudeDo.Ui/ViewModels/Modals/WorktreesOverviewModalViewModel.cs
@@ -192,10 +192,18 @@ public sealed partial class WorktreesOverviewModalViewModel : ViewModelBase
 
     [RelayCommand]
     private void Close()
+    {
+        StopReconcileTick();
+        CloseAction?.Invoke();
+    }
+
+    /// <summary>Stops the reconcile tick. Also called from the dialog's native-close fallback
+    /// (WindowDialogService), which bypasses <see cref="CloseCommand"/> — otherwise an Alt+F4
+    /// leaves the timer re-running LoadAsync (git + DB) on an orphaned VM. Idempotent.</summary>
+    internal void StopReconcileTick()
     {
         _reconcileTimer.Stop();
         _reconcileTimer.Dispose();
-        CloseAction?.Invoke();
     }
 
     [RelayCommand]
diff --git a/src/ClaudeDo.Ui/Views/WindowDialogService.cs b/src/ClaudeDo.Ui/Views/WindowDialogService.cs
index 9ccad7e3..812b5e54 100644
--- a/src/ClaudeDo.Ui/Views/WindowDialogService.cs
+++ b/src/ClaudeDo.Ui/Views/WindowDialogService.cs
@@ -107,6 +107,7 @@ public sealed class WindowDialogService : IDialogService
     {
         var dlg = new WorktreesOverviewModalView { DataContext = vm };
         vm.CloseAction = () => dlg.Close();
+        dlg.Closed += (_, _) => vm.StopReconcileTick();   // native close bypasses CloseCommand
         vm.JumpToTaskAction = (listId, taskId) =>
         {
             if (Shell is { } s) _ = JumpToTaskHelper.SelectAsync(s, listId, taskId);
@@ -161,6 +162,7 @@ public sealed class WindowDialogService : IDialogService
     {
         var dlg = new LogVisualizerView { DataContext = vm };
         vm.CloseAction = () => dlg.Close();
+        dlg.Closed += (_, _) => vm.StopReconcileTick();   // native close bypasses CloseCommand
         await dlg.ShowDialog(_owner);
     }