Link tasks to their restarts

Closes #1711 (closed)

arkindex/ponos/api.py

@@ -236,6 +236,10 @@ class TaskRestart(ProcessACLMixin, CreateAPIView):
 
         # Rename the original task
         basename, *_ = copy.slug.rsplit("_old", 1)
+        if copy.original_task_id:
+            basename, *_ = copy.slug.rsplit("_old", 1)
+        else:
+            basename = copy.slug
         latest_task = Task.objects.filter(run=copy.run, slug__startswith=f"{basename}_old").order_by("-created").first()
         if not latest_task:
             # There is no previously restarted task: the original task will have the slug slug_old1