fix(worker): block approve of a planning parent with an unfinished child, surface git stderr on ff failure

src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs

@@ -1013,6 +1013,20 @@ public sealed class TaskMergeService
         if (task.Status != TaskStatus.WaitingForReview)
             return Blocked("task is not waiting for review");
 
+        // A plan lands whole or not at all -- same rule (and message) as PlanningMergeOrchestrator.StartAsync,
+        // which a unit-branch parent no longer passes through.
+        if (task.PlanningPhase != PlanningPhase.None)
+        {
+            using var ctx = _dbFactory.CreateDbContext();
+            var notDone = await ctx.Tasks.AsNoTracking()
+                .Where(c => c.ParentTaskId == taskId && c.Status != TaskStatus.Done)
+                .OrderBy(c => c.SortOrder)
+                .Select(c => new { c.Id, c.Status })
+                .FirstOrDefaultAsync(ct);
+            if (notDone is not null)
+                return Blocked($"subtask {notDone.Id} is not Done (status {notDone.Status})");
+        }
+
         // An interactive child of a unit lands in the unit branch, not on the target; the parent's
         // own approve merges the unit. A failed fast-forward keeps the child in review.
         if (task.ParentTaskId is not null && _unitBranch is not null)