Yep, that is correct. I think ldump is able to preserve all upvalues, even on edge cases such as "_ENV" and joined upvalues (multiple functions referencing one

Yep, that is correct. I think ldump is able to preserve all upvalues, even on edge cases such as "_ENV" and joined upvalues (multiple functions referencing one upvalue). A closure is basically an object with a single method and upvalues as fields -- serialization is straightforward. I think I got it covered, but I would be glad to hear ideas about where the serialization can be unstable.