fix(ui): drop stale delta refreshes so the newest task state wins

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

@@ -25,6 +25,10 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
     // pick the flag up (see SyncInteractiveSessions).
     private readonly HashSet<string> _interactiveSessionIds = new();
     private static readonly TaskListFilterRegistry _filters = new();
+    // Two events (TaskUpdated + WorktreeUpdated) drive the same delta refresh, so two reads for
+    // one task can be in flight at once. Only the newest may write to the row.
+    private readonly Dictionary<string, long> _deltaSeq = new();
+    private long _deltaCounter;
 
     public event EventHandler? SelectionChanged;
     public event EventHandler? FocusAddTaskRequested;
@@ -179,9 +183,12 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
             return;
         }
 
+        var seq = ++_deltaCounter;
+        _deltaSeq[taskId] = seq;
+
         try
         {
-            await ApplyDeltaAsync(taskId, list);
+            await ApplyDeltaAsync(taskId, list, seq);
         }
         catch (Exception first)
         {
@@ -189,7 +196,7 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
                 $"TasksIsland: delta refresh for {taskId} failed ({first.Message}); retrying");
             try
             {
-                await ApplyDeltaAsync(taskId, list);
+                await ApplyDeltaAsync(taskId, list, seq);
             }
             catch (Exception second)
             {
@@ -200,7 +207,7 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
         }
     }
 
-    private async Task ApplyDeltaAsync(string taskId, ListNavItemViewModel list)
+    private async Task ApplyDeltaAsync(string taskId, ListNavItemViewModel list, long seq)
     {
         await using var db = await _dbFactory.CreateDbContextAsync();
         var entity = await db.Tasks
@@ -208,6 +215,9 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
             .Include(t => t.Worktree)
             .FirstOrDefaultAsync(t => t.Id == taskId);
 
+        // A newer refresh for this task started while we were reading — its result is fresher.
+        if (_deltaSeq.TryGetValue(taskId, out var current) && current != seq) return;
+
         // A parent transition (finalize/discard) broadcasts only the parent's id, but it
         // changes its children's derived state — finalize flips them Draft→Planned, discard
         // deletes them. The delta path below only touches the parent row and never recomputes

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

@@ -122,4 +122,32 @@ public class TasksIslandDeltaResilienceTests : IDisposable
 
         Assert.Equal(TaskStatus.Running, vm.Items.Single(r => r.Id == "T1").Status);
     }
+
+    [Fact]
+    public async Task A_stale_delta_result_does_not_overwrite_a_newer_one()
+    {
+        await SeedAsync();
+
+        var factory = new FlakyDbFactory(NewContext, failuresLeft: 0);
+        var vm = new TasksIslandViewModel(factory, new FakeWorker());
+        var list = UserList("L1", "Work");
+        await LoadAndWaitAsync(vm, list);
+
+        // Start refresh #1 while the DB still says Queued, but do not await it yet.
+        var first = vm.RefreshTaskFromWorkerAsync("T1");
+
+        await using (var db = NewContext())
+        {
+            var t = await db.Tasks.FirstAsync(x => x.Id == "T1");
+            t.Status = TaskStatus.Running;
+            await db.SaveChangesAsync();
+        }
+
+        // Refresh #2 sees Running and must win, regardless of completion order.
+        var second = vm.RefreshTaskFromWorkerAsync("T1");
+
+        await Task.WhenAll(first, second);
+
+        Assert.Equal(TaskStatus.Running, vm.Items.Single(r => r.Id == "T1").Status);
+    }
 }