> both sides have to agree to the "limited" part for it to stay limited
It’s more that each side has to moderate itself. That’s true if both have nukes or just one. And it’s much easier to moderate oneself when it’s in one’s own interest, e.g. to avoid getting nuked.
Both sides have to agree to the "limited" part for it to stay limited. Mind you, threats of nuclear escalation are routine from Russia.