Constant tea_sdk::runtime::ops::replica::OP_REV_FOLLOWUP

pub const OP_REV_FOLLOWUP: &'static str;

If return a empty vec, the replica is still waiting for the second part of the txn - followup pair. If this is the second part, the pair is completed, it will return the tsid as bytes. In this case, please generate the sync message to other replica, because this replica found a new txn that need to notify others