Each instantiated module has its own complete function call stack. A call out of the module, to a bit of control code in JS, and then into a different instance

Each instantiated module has its own complete function call stack. A call out of the module, to a bit of control code in JS, and then into a different instance of the same module, with the same memory mappings, would look (to the program itself) like a stack switch, no? I guess it raises the philosophical question of what is a stack switch, anyway? If you end up cooperatively running multiple "green threads" within a single "OS thread" does it matter that what you actually switched was the entire execution environment?