I worked for a summer as a kid doing tire repair. The place also was a Bondag cold cap repair for semi truck tires. I only worked there a few times when they needed an extra hand. They would grind the old tread off, and they had preformed tread material that would get rolled on with a thin rubber glue strip. Then they would put it in this same rubber outer envelope, and a split rim was put in from either side. It would go into an autoclave with 30 or so other tires. Each tire had a airline to the inner and outer to pressurize. They autoclave was a pressure vessel as well, and I think the thermal cure was done overnight. This was in 1975. I don't see Bondag around anymore. They also sold hot cap retreads for automotive. And I don't see them anymore either, but they were done in some factory where the old tread was ground off, and new tread injection molded onto the carcass.
For truck tires, the best carcasses were Michelin, as they could be redone 4-5 times. Memory was this was around a half million miles.
It was a good job for the summer as I learned to use tire spoons and remove truck and automotive tubeless tires, and I still do my own tires today. And I got a dynamic balancer so spin balance myself as well. And I don't have to wait to have it done in the shop.