Given that we are talking about JavaScript, I meant the former.

The latter is pretty much the status quo in terms of the state of the art. Most kernels aren't built with automatic reference counting, reference counted objects are plentiful even if more manual, but the automatic part is trivial to add to a C++ code base using smart pointers for example, and things like rust or apple ARC can also do it.

I think the former (a "true" GC that can resolve cycles) could be done in a kernel, it's just not common.

I'm not well versed in this historical example, did the "lisp machine" not have a GC in its OS?