The primary issue here is that the whole value after @@ is a single string. The fragment logic is replacing ? with the parameter replacements, but postgres doesn’t accept parameters just inside of a string like that.
Try replacing your filter with this preparation. Note that I’ve also used the expression syntax to interpolate the names reference. You should do this instead of putting in names literally as that can cause ambiguous queries.
prepare fn query, _ ->
jsonpath = '($[*].surname like_regex \"^#{query.arguments.name}\" flag \"i\") || ($[*].given_name like_regex \"^#{query.arguments.name}\" flag \"i\")'
Ash.Query.filter(query, fragment("to_json(?)::jsonb @@ ?", names, jsonpath)
end
