Protobuf and the app are behaving the right way. 99.999% of users aren't going to MitM your protocol.
How exactly should you deploy client code to the edge, which may not be updated, to handle "unknown" tag number fields? You don't, because that's crazy. Nobody should write software like that because it creates a maintenance hell where you can't upgrade or downgrade because "smart" applications are doing stupid, undeterministic things with the protocol.
It's impossible to reason and engineer backward / forward compatibility when you don't treat the wire format and API with respect.
Most of the major migration headaches I've had in my career have been the result of engineers trying to be clever in the time and place they wrote the code.
How exactly should you deploy client code to the edge, which may not be updated, to handle "unknown" tag number fields? You don't, because that's crazy. Nobody should write software like that because it creates a maintenance hell where you can't upgrade or downgrade because "smart" applications are doing stupid, undeterministic things with the protocol.
It's impossible to reason and engineer backward / forward compatibility when you don't treat the wire format and API with respect.
Most of the major migration headaches I've had in my career have been the result of engineers trying to be clever in the time and place they wrote the code.