a) - yes I agree, although these flags are now completely general aren't they? So although IFEnocache makes no sense for client to provide and/or a lot more sense for server.. going forward if make still make sense to pass in 'extraFlags'

b) - Yes, need to be very careful a old client, that doesn't send this extra byte, sending to a new server, doesn't try to deserialize the non-existent bytes..