Question for Subaru techs: ruling out timing belt as failure point (EJ22).

The gf's 1st gen Legacy (EJ22, non-turbo) refused to start today (good thing there was another 1st gen Legacy around to drive instead). It cranks and fires like it wants to start but won't. When you take the key from start back to run the engine kicks back a little bit so if you lay on the starter during that brief time it makes an unpleasant noise and seems like it's trying to fire backwards. It I hadn't moved it earlier today I would say it has no compression because when it tries to start and sputters and tries to start like it has no compression. This and the way it sometimes kicks back like it's trying to rotate backwards makes me think valve timing (i.e. timing belt) is not right.

It has ~160k on it. I have no idea when the timing belt was done last. Since it's non-interference and there's other shitboxes around to drive it really hasn't been a priority until now.

How do I confirm or rule out timing belt as the failure point before I dive into this?

I know that the belt isn't straight up broken because it coughs and tries to start but if it slipped a tooth or several that could cause my symptoms.

I know this is a long shot because Reddit only wrenches new-ish cars and the knowledge here begins and ends with Alldata but if there's anyone familiar with these older cars who can save me some time I'd appreciate it.