Fleeting notes should be processed into permanent notes
Fleeting notes are a useful way to capture fragile ideas as they are formed.
Literature notes are a subcategory of fleeting notes.
Neither one should hang around in this Zettelkasten.
The ideas need to be digested: turned into zettels using a thought framework to connect them to the larger knowledge framework.
There is no need (and in fact probably a detriment) to keep the original brainstorming thoughts around cluttering up searches and whatnot.