-type update() :: #{mem := false,
                    origin := classy:site() | undefined,
                    clock := clock() | undefined} |
                  #{mem := true, clock := clock(),
                    host => node(), meta => map(),
                    liveness =>
                        {_NRestarts :: non_neg_integer(),
                         _SetBySelf :: boolean(),
                         _IsLive :: boolean()}}.