restricting posting to certain categories by user or role…

hi,
i’m looking into adding functionality to restrict certain users to only be able to post in certain categories. but wordpress doesn’t seem to have any api hooks in it’s backend for this. i’ve written plugins before and have spent a lot of time looking at this code. the new “terms” way of doing things in 2.3 seems to de-evolve categories to the level of tags.

the easiest example is a newspaper where you’d want the sports editor to only be allow to post to the sports category, news to news, etc. i’d settle for excluding certain cats based on roles as well, but so far i can’t find any existing code/plugins/help in any way and i’ve been at it for weeks. it seems i’d have to hack the very code, thereby destabilizing wordpress and my projects.

does anyone know a solution to what should be a common requirement for many multi-user blogs. maybe i’m missing something obvious.

thanks for any help.
– lawrence