I think my caching problem is fixed

A post will follow shortly (hopefully) outlining the pain I went through to get it working again.
 
(And yes, this does serve as a test post for the changes I just battled with)
EDIT: Turns out it isn’t yet. Will keep trying.
EDIT 2: Only problem left seems to be invalidating the main page cache on posting / editing posts. It automatically expires fine though.
EDIT 3: Debug might be helpful?