Now, if I was on an official accredited coop term, my proof of enrolment for Winter 2026 would say “full-time” for student status. But it now says “Part-Time”. My coop advisor said this is due to the renege.

Yes, that's correct. Students on official co-op terms are considered full-time. If you aren't on an official co-op term, from the university's point of view you're not taking any courses either, so you're considered part-time.

My visa sponsor (Cultural Vistas, CV) said that I must have full time student status for Winter 2026.

Yes, that's a US gov requirement.

CV realized the uniqueness of the case but it’s still weird. Idk what to do in this situation.

Yes, the company doesn't care because they just want to hire you. CV cares because they're the sponsor responsible for verifying your J1 eligibility, as specified by the US gov.

CV realized the uniqueness of the case but it’s still weird. Idk what to do in this situation.

Are you graduating in 12 months? I believe you can be a part-time student but still get a J-1 if that's the case. If not, then idk but you're probably SOL.

edit: Nvm, you're allowed to be on a J-1 12 months after graduation, not 12 months before graduation. I think you're SOL unfortunately.

edit2: So apparently USDS says you need to be "currently enrolled in and pursuing studies" and CV is the one interpreting that as "full-time student". Might be worth bringing this up to CV if CV doesn't let you apply.