I suspect writing bad code with poor documentation has nothing to do with autism. I'd suggest don't treat him different than any other employee.
If he steals work he steals work, less to be done by you. If he crashes and burns, so be it.
If he steals work he steals work, less to be done by you. If he crashes and burns, so be it.
If he were the tech lead I do not think he would steal work, he'd just delegate it. I think OP and the 10x programmer are peers and they are in an unhealthy competition.