Once consensus is reached on a value, Paxos must force future coordinators to select that same value
in order to ensure continued agreement. To guarantee this, the promise messages from replicas include the
most recent value they have heard, if any, along with the sequence number of the coordinator from whom
they heard it. The new coordinator chooses the value from the most recent coordinator. If none of the
promise messages contain a value, the coordinator is free to choose a submitted value.