International MSCS students - legal ways to work at a startup during studies?

Incoming USC Viterbi MSCS student here (international, F-1). I'm interested in working part-time at a tech startup during my studies (founder is my close friend). What are the legal options for doing this?

From what I understand, on-campus jobs are limited to 20 hrs/week during the semester. But what about off-campus work at a startup? Is CPT the only route, and can it be used part-time during the academic year (not just summer)? Has anyone done this successfully?

Also curious if anyone has experience with startup-related work that falls into a gray area - like contributing to an open-source project tied to a startup, doing unpaid "advising," or working on your own side project that generates revenue. Where does USC draw the line?

Any advice from international students who've navigated this would be really appreciated.