I'm leaving the door open for other people to write code that might want to take some number and subtract it from the current page number, and having their staging data get messed up or something and have the result come back as -5.

Instead of silently giving them a valid page, let them know that their tests somehow produced an invalid page number. Same goes for those who try to add numbers to the current page number. These sorts of exceptions will complain when you do something invalid, highlighting smelly code and hopefully raising the suspicions of whoever is watching the CI server output during test runs.