https://www.callahan-law.com/are-non-competes-enforceable-in...
Specifically California Business and Professions Code Section 16600,
“every contract by which anyone is restrained from engaging in a lawful profession, trade, or business of any kind is to that extent void.”
In addition such issues must by law be decided in California courts and if they forced the issue into court and lost they would be liable for the cost of his defense.
Even outside of California there are limits to what you can enforce. Judges aren't liable to find that an infinite duration noncompete reasonable.
Another example in Washington State its now impossible to obtain noncompetes for anyone paid less than a rate of 100k per annum as an employee or 250k per annum as a contractor and they are limited to 18 months duration.
If you improperly assert a noncompete you are liable for 5000 or actual damages whichever is greater.
They are probably not asserting a noncompete because it is functionally impossible for them to do so. They would have to assert that he was making use of trade secrets or that in some nebulous way his design belonged to them. eg trade dress
https://www.findlaw.com/smallbusiness/intellectual-property/...
The answer is you need a lawsuit to decide but probably not.
Still didn't stop everyone I've ever worked for from making me sign them, enforceable or not. I guess it's different elsewhere.
(That also says nothing about whether such a contract has or has not been signed by the relevant parties.)
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.
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.
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...)
If that was the case almost everyone with a GitHub project could be sued to infinity, because almost everyone learns tons of things every day while working.