TODO Remember that the code is more complicated than the messaging. Let the messages absorb some of the complexity of the code. (Divide them. Restrict their structure.)
function Recorder (paxos) {
    var entry = paxos.log.head.body
    this.register = {
        body: {
            promise: entry.promise,
            body: entry.body,
            previous: entry.previous
        },
        previous: null
    }
    this._paxos = paxos
}