I don't live anywhere near California (Québec), but it's kinda the same idea here (from what I've heard). Basically employees have the right to make a living and the onus is on the employer to prove an injury occured directly due to an (ex)employee's actions.

Still didn't stop everyone I've ever worked for from making me sign them, enforceable or not. I guess it's different elsewhere.

He might have signed one but it would be legally invalid and if pressed in court it would cease to exist in 0.5 seconds it wouldn't be worth the time to present.

I fail to see how "you can't copy our product" is the same as "restrain[ing] from engaging in a lawful profession, trade, or business of any kind".

(That also says nothing about whether such a contract has or has not been signed by the relevant parties.)

As always seem to need a lawyer to be absolutely sure about any complex matter of law but it looks to me like creating even an identical product which this is not would fall within the scope of "any lawful profession, trade, or business of any kind" for clarity I read that as you can't stop a person from doing any of the above from a b and c rather than you can't stop someone from doing all of a b c.

I don't think Repl.it has a leg to stand on they just have a pile of money and the presumption of being willing and able to hire a shark in a suit to ruin someone's life with a baseless suit filed for the sake of harassment.

Copyright infringement is not a lawful profession, trade, or business.

It's not clear to me that implementing the same concept after having seen and written some of their code constitutes copyright infringement.

If you hire an intern to work on your code base you own merely own the work that person creates for the duration of their internship. Your piddling money doesn't buy you the general knowledge of how such a solution works any more than an auto shop acquires by dint of buying a few hours of labor owns the mechanics understanding of how a transmission works.

Have you ever reimplemented something from scratch, perhaps in a different language, and ended up doing something in the same way as the original code? ... I sure have.

I would think that a few chunks of very similar code, and a well-paid expert testifying, plus the fact that he had knowledge of Replit's code from his employment, would go a long way towards a tough time in court for both parties. (Or, at the very least, that they both need to talk to lawyers before/when they start throwing around legal threats...)