Prevent scheduler callbacks after cancellation

internal/framework/llm/scheduler.go

@@ -83,6 +83,9 @@ func (s *Scheduler) Run(ctx context.Context, fn func(context.Context) error) err
 		return err
 	}
 	defer release()
+	if err := ctx.Err(); err != nil {
+		return err
+	}
 	return fn(ctx)
 }