These two are together because you wouldn’t bother brainstorming unless there is a problem to be solved, and you rarely solve a problem without a little brainstorming. Regardless of the specific purpose, a short agenda should be enough to keep the session from straying off-course.
The key here is to choose the right people to collaborate with. Diverse knowledge, skills, backgrounds, and opinions are incredibly valuable in this context. Of course, all that diversity is for naught without trust. Participants need to feel safe voicing dissenting opinions.