25ccb5c75b
heid-bug-hunt panel (Gróa + Hulda, confirmed-from-code) caught that a truthy
non-dict `sort` (e.g. sort="updated_at" or sort=["updated_at"]) reached
`(sort or {}).get(...)` and crashed with AttributeError instead of the
InvalidArguments PRE-003 promises for malformed caller-controlled input. Add an
isinstance guard before field extraction. Test covers str/list/int sort values.