As I was writing the surface sync API doc, I realized how much I hate fallback surfaces. It's bad API design because it's something the system SHOULD already know about but we're asking clients to do regardless.

Clients shouldn't need to WORRY about fallbacks, that's surface sync internal magic.

Saman had some brilliant ideas (as usual) about getting rid of explicit fallbacks:

https://docs.google.com/presentation/d/10z7N99A2HdGbAxLryF0QL3uymCkEYIaYYWHTbLDy3vE/edit#slide=id.p