"Can three to four years of public sector work experience before law school hurt you when applying to a summer associate position? How can this be framed in a positive way for regulatory enforcement work?"
There's nothing wrong with having public sector work experience and having that on your resume. That's actually good. You wanna put as little information as possible, not bragging about all these different accomplishments related to it, but if it's related to regulatory enforcement work, I would highlight the things that are related to that. So you need to know your audience.