I agree with with what's proposed in the question both for the reason mentioned in a comment:
...there should be no need to go to another site to read the question.
and because what happens in one site can't be controlled on another site, and there's not even a notification process; if the other post is altered or deleted this is not communicated back here so there's no opportunity to respond.
In Stack Exchange we do whatever we can that is practical to future-proof posts. We strongly discourage link-only answers for this reason.
SO we should also try to future-proof questions as well to the extent practical, and a bit of copy/paste/edit is all that's needed here.
The OP should do that, and if there's no response after a while probably someone should go ahead and do it.
Since it's the same OP for both posts, this should be trivial. Nobody can maintain all their posts forever and anyone can edit a post in the future, so duplication is called for in this case.