By necessity, when you’re in the debugger your code has already been compiled either way, no? Or am I missing something here?

This isn’t executing your code as you’re writing it (though it does support Edit & Continue), this is preemptively executing the next lines in your code when you’re already paused in the debugger - which means it’s been compiled and already running.

you're misunderstanding. this is a function of the debugger. Your code has already been compiled and is currently running if you are using this feature.