I'm not sure I understand the argument, why is the halting problem even important here? Surely a compiler can split loops into ones that halt so they only run a

I'm not sure I understand the argument, why is the halting problem even important here? Surely a compiler can split loops into ones that halt so they only run a little bit at a time. But you don't necessarily need a compiler for that, OS can help too and, for example, invoke a signal handler from which you can stop currently running actor. Actors can be safely stopped, destroyed, preempted, etc. without breaking other actors.