added first_error for asyncio task groups

src/monitor_utils/runner.py

@@ -553,3 +553,12 @@ async def retry_failed_pages(
         retry_attempt += 1
 
     return failed_pages
+
+
+def first_error(group_exc: BaseExceptionGroup) -> BaseException:
+    """Return the first leaf exception of a possibly nested exception group."""
+    error = group_exc.exceptions[0]
+    while isinstance(error, BaseExceptionGroup):
+        error = error.exceptions[0]
+
+    return error