TLDR: We should consider having application level errors as a part of the gRPC responses, to make it easier to identify them.

For example in the following line:

failed to CloseAndRecv is not necessarily correct, as err is whatever is returned from the following function:
.

Not sure what's the best solution (need to do some research), but we could add an error(s) field to gRPC responses so we have a clear separation between application level errors and gRPC/communication level ones.

Also due to grpc/grpc-go#2934 we can't unwrap errors.