fix export errors

backend/main.py

@@ -301,6 +301,8 @@ Generated by ROCmPort AI.
                 "Content-Disposition": "attachment; filename=rocmport_migration.zip"}
         )
 
+    except HTTPException:
+        raise
     except Exception as e:
         raise HTTPException(
             status_code=500, detail=f"Export failed: {str(e)}") from e