Update app.py

app.py

@@ -510,6 +510,7 @@ def _get_mem_used_gb() -> float:
     return psutil.virtual_memory().used / (1024 ** 3)
 
 
+class _WD:
     level = "ok"; ram_gb = 0.0; flushes = 0; rejects = 0
 wd = _WD()