(Was just closing tabs, and noticed that the following message from yesterday didn't get sent properly)

Yeah, the cleanup issue was one I was wondering about -- presumably, old cache files will start getting cleaned up when the cache reaches a max size?

Theoretically, things could change in a video.html, exercise.html, topic.html, or other cached template, between within-version updates (where only `BUILD` changes).

Maybe (again, just thoughts for later; fine to go with `VERSION` for now) we want a separate counter to increment whenever something cacheable changes, so that we don't need to invalidate everything for versions where nothing cacheable changed. Or perhaps the update process itself can notice which templates changed, and intelligently know which views need invalidating. What if the KEY_PREFIX for a view were a concatenation of the hashes of each of the template files it depended on, and any other variables (e.g. settings) that affected the rendering of the view? Anyway, just throwing ideas out there, we don't need to get that fancy yet (ever?).