There's no need to pull the proto file on every build. Proto also has a set of rules for how to maintain wire-compatibility across versions[1]. Following those rules and distributing the definition only when you need new fields should be sufficient.

That said; If you've got a set of shared proto definitions, you should probably either go to a monorepo, or share the shared bits with a git submodule. Doesn't prevent you from needing to follow those conventions, but does make it far easier to debug when things changed.

[1] https://developers.google.com/protocol-buffers/docs/proto3#u...