fix(worker,ui): route details-pane task delete through worker to advance blocked parents

Deleting a child from the details pane hard-deleted straight from the UI
process via TaskRepository, bypassing TaskStateService.TryAdvanceParentAsync
entirely. Deleting the last child of a WaitingForChildren parent that way
left it wedged forever. WorkerHub.DeleteTask now mirrors the MCP delete_task
tool (running-task guard, FK-friendly error, advance-parent call), and the
UI goes through it.

TryAdvanceParentAsync also short-circuited when zero children remained,
treating "no children left" as "nothing to evaluate" instead of "all done" -
removed the early return so an empty child list (vacuously) counts as all
terminal.

src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs

@@ -57,6 +57,10 @@ public interface IWorkerClient : INotifyPropertyChanged
     Task<PendingQuestionDto?> GetPendingQuestionAsync(string taskId);
     Task ResetTaskAsync(string taskId);
     Task CancelTaskAsync(string taskId);
+    /// <summary>Deletes a task via the worker (mirrors the MCP delete_task tool), so a deleted
+    /// child correctly advances a WaitingForChildren parent. Returns (false, message) instead of
+    /// throwing when the task has children or is running, preserving the FK-error UX.</summary>
+    Task<(bool Ok, string? Error)> DeleteTaskAsync(string taskId);
     Task<List<AgentInfo>> GetAgentsAsync();
     Task RefreshAgentsAsync();
     Task<SeedResultDto?> RestoreDefaultAgentsAsync();

src/ClaudeDo.Ui/Services/WorkerClient.cs

@@ -327,6 +327,19 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
         await _hub.InvokeAsync("CancelTask", taskId);
     }
 
+    public async Task<(bool Ok, string? Error)> DeleteTaskAsync(string taskId)
+    {
+        try
+        {
+            await _hub.InvokeAsync("DeleteTask", taskId, CancellationToken.None);
+            return (true, null);
+        }
+        catch (HubException ex)
+        {
+            return (false, ex.Message);
+        }
+    }
+
     public async Task WakeQueueAsync()
     {
         await _hub.InvokeAsync("WakeQueue");

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

@@ -946,18 +946,14 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             var ok = await ConfirmAsync($"Delete \"{row.Title}\"? This cannot be undone.");
             if (!ok) return;
         }
-        try
-        {
-            await using var ctx = _dbFactory.CreateDbContext();
-            var repo = new TaskRepository(ctx);
-            await repo.DeleteAsync(row.Id);
-        }
-        catch (Microsoft.EntityFrameworkCore.DbUpdateException ex) when (
-               ex.Message.Contains("FOREIGN KEY", StringComparison.OrdinalIgnoreCase)
-            || ex.InnerException?.Message.Contains("FOREIGN KEY", StringComparison.OrdinalIgnoreCase) == true)
+        // Routed through the worker (mirrors the MCP delete_task tool) so a deleted child
+        // correctly advances a WaitingForChildren parent — a direct-repo delete from here used
+        // to bypass TaskStateService.TryAdvanceParentAsync and could wedge the parent forever.
+        var (deleted, error) = await _worker.DeleteTaskAsync(row.Id);
+        if (!deleted)
         {
             if (ShowErrorAsync != null)
-                await ShowErrorAsync("This task has child tasks. Discard the planning session or delete child tasks first.");
+                await ShowErrorAsync(error ?? "Delete failed.");
             return;
         }
         if (DeleteFromList != null)