So you're suggesting that, for example, if Open Street Map makes a new logo, we'd add it as `www/assets/openstreetmap-2.png`? A year from now, I doubt we're going to remember to do that.

I think I'd prefer for everything to be under `%version`. It means a 100% cache miss on the first page after a new deploy, but every page after that has a 100% cache hit (for assets at least).