This can be done using interfaces.py with:

  from roundup.rest import RestfulInstance
  RestfulInstance.max_response_row_size = 25

which limits the number of rows returned to 24 (one less than the setting).

With this in place:

   https://example.net/demo/rest/data/issue?@page_size=25

returns:

  {
    "error": {
        "status": 400,
        "msg": "Page size 25 must be less than admin limit on query result size: 25."
    }
  }

I think this is sufficient. I don't expect it to be used often. The default
limit is 10M rows.