Thanks so much @haberman! Yep, the whole thing is a little bit confusing... We basically focused on two things:

- not using extensions, as 3 does not support it - not using map, as 2 does not support it

and we basically landed on restricting ourselves to use the common denominator among all post-2.5 versions. Wondering if this sounds reasonable to you - always great to hear the original author's advice.

Plus, I am wondering if there are recommended ways of reducing protobuf runtime size, we use protobuf-lite but if there are any further wins it would be definitely nice for memory and space constrained problems.