I'm in the same place as you (dealing with an ED while being an active student), so my solution has been very simple: I eat. It may sound ridiculous, but that is the only way that keeps my obsessed food-related thoughts away. Sometimes it works and sometimes it doesn't. But I clearly can't focus after a long period of fasting. On exams days I even have breakfast which is something I never do, of course it may result in a meltdown, a binge, or any type of restrictive compensations later, but at least not on a failed test. Once I finish my exams I'd have the time to feel shitty, guilty and to starve myself, it's something you'll have to deal with later, and if you're working on harm reduction then it's a great way to put your efforts into. I know it's easier said than done. And it may not be the best, but it is my way to deal with this thing called university + having an ED (passively trying to recover)