Interesting, wonder if some startup that didn't want to deal with the risk could just have a checkbox if you have a current in-effect non-compete agreement and just pipe those applications to /dev/null? Maybe if more companies were picky, people would fight back and try to negotiate better agreements... but then again probably depends on location, In Silicon Valley you can be a more picky potential employee compared to say rural Ohio.

How would you know? What would someone intentionally violating noncompete mention it to an employer?

Lying to a potential employer is a pretty bad first step. If I caught you doing it, say because someone mentioned it in a casual conversation, I'm going to fire you the same day. Same with lying on a resume even if it's utterly irrelevant multiple years later. It's also going to color any future professional interaction because you're an untrustworthy individual.

I'm pretty sure I don't want to be in a position where I'd be fired if a 10-year old lie came out.