fix(ui): prevent dragging completed tasks in the task list

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/ClaudeDo.Ui/ViewModels/Islands/TasksIslandViewModel.cs

@@ -1009,6 +1009,7 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
     {
         if (!CanReorder || _currentList is null) return;
         if (source.IsRunning || target.IsRunning) return;
+        if (source.Done || target.Done) return;
         if (ReferenceEquals(source, target)) return;
 
         // Master Items: single Move event (no Reset) so ItemsControls animate, not rebuild.

src/ClaudeDo.Ui/Views/Islands/TasksIslandView.axaml.cs

@@ -94,8 +94,8 @@ public partial class TasksIslandView : UserControl
             && parentVisual.FindAncestorOfType<Button>() is not null;
         if (nestedInsideButton) return;
 
-        // Running tasks can be neither reordered nor re-queued.
-        if (row.IsRunning) return;
+        // Running and completed tasks can be neither reordered, moved nor re-queued.
+        if (row.IsRunning || row.Done) return;
 
         // Arm the drag for ANY list kind so drag-to-queue works everywhere; reorder-on-drop is
         // still gated on CanReorder (user lists only).
@@ -173,7 +173,7 @@ public partial class TasksIslandView : UserControl
         {
             var targetButton = RowButtonAt(e, topLevel);
             if (targetButton?.DataContext is TaskRowViewModel target
-                && !ReferenceEquals(target, row) && !target.IsRunning)
+                && !ReferenceEquals(target, row) && !target.IsRunning && !target.Done)
             {
                 var placeBelow = e.GetPosition(targetButton).Y > targetButton.Bounds.Height / 2;
                 await vm.ReorderAsync(row, target, placeBelow);
@@ -223,7 +223,7 @@ public partial class TasksIslandView : UserControl
 
         var targetButton = RowButtonAt(e, topLevel);
         if (targetButton?.DataContext is not TaskRowViewModel target
-            || target.IsRunning || ReferenceEquals(target, _pressRow))
+            || target.IsRunning || target.Done || ReferenceEquals(target, _pressRow))
         {
             vm.ClearDropHints();
             return;
@@ -238,7 +238,7 @@ public partial class TasksIslandView : UserControl
         if (placeBelow)
         {
             var next = FindNextInSameSection(vm, target);
-            if (next is not null && !next.IsRunning) { hintRow = next; hintBelow = false; }
+            if (next is not null && !next.IsRunning && !next.Done) { hintRow = next; hintBelow = false; }
             else { hintRow = target; hintBelow = true; }
         }
 

tests/ClaudeDo.Ui.Tests/ViewModels/TasksIslandRegroupTests.cs

@@ -347,6 +347,27 @@ public class TasksIslandRegroupTests : IDisposable
         Assert.Equal(new[] { "t2", "t3", "t1" }, vm.Rows.OfType<TaskRowViewModel>().Select(r => r.Id));
     }
 
+    [Fact]
+    public async Task ReorderAsync_WithDoneSourceOrTarget_IsNoOp()
+    {
+        await SeedTasksAsync(
+            ("t1", TaskStatus.Idle, null, 0),
+            ("t2", TaskStatus.Idle, null, 1),
+            ("t3", TaskStatus.Done, null, 2));
+
+        var vm = BuildViewModel();
+        await LoadAndWaitAsync(vm, UserList("list1", "Default"));
+
+        var t1 = vm.Items.First(r => r.Id == "t1");
+        var t3 = vm.Items.First(r => r.Id == "t3");
+        var before = vm.Items.Select(r => r.Id).ToList();
+
+        await vm.ReorderAsync(t1, t3, placeBelow: true);
+        await vm.ReorderAsync(t3, t1, placeBelow: false);
+
+        Assert.Equal(before, vm.Items.Select(r => r.Id));
+    }
+
     [Fact]
     public async Task SetScheduledForAsync_LocalDateTime_PersistsAsUtc()
     {