feat(worker): allow update_task_status to set Cancelled

src/ClaudeDo.Worker/State/TaskStateService.cs

@@ -241,7 +241,13 @@ public sealed class TaskStateService : ITaskStateService
         return new TransitionResult(true, null);
     }
 
-    public async Task<TransitionResult> CancelAsync(string taskId, DateTime finishedAt, CancellationToken ct)
+    // allowFromIdle: only the external update_task_status(Cancelled) path sets this — it lets
+    // an Idle task be retired without deleting it. Every other caller (hub CancelReview,
+    // PlanningChainCoordinator's chain-walk, batch cancel) relies on Idle staying a no-op here;
+    // PlanningChainCoordinator specifically uses "parked back to Idle" as a deliberate opt-out
+    // signal, so do not flip this default.
+    public async Task<TransitionResult> CancelAsync(
+        string taskId, DateTime finishedAt, CancellationToken ct, bool allowFromIdle = false)
     {
         List<string> cancelledChildIds;
         await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
@@ -250,7 +256,8 @@ public sealed class TaskStateService : ITaskStateService
                 .Where(t => t.Id == taskId &&
                     (t.Status == TaskStatus.Running || t.Status == TaskStatus.Queued
                      || t.Status == TaskStatus.WaitingForReview
-                     || t.Status == TaskStatus.WaitingForChildren))
+                     || t.Status == TaskStatus.WaitingForChildren
+                     || (allowFromIdle && t.Status == TaskStatus.Idle)))
                 .ExecuteUpdateAsync(s => s
                     .SetProperty(t => t.Status, TaskStatus.Cancelled)
                     .SetProperty(t => t.FinishedAt, finishedAt), ct);