-- The order of what a machine was sent, so a host can tell an older declaration from a newer.
--
-- novox/hq 04-ISSUES/107. A declaration's only identity was the digest of its bytes. The host could
-- say "this is not the last one" and could not say "this is older", so a backlog drained out of
-- order applied a declaration the mesh had already superseded. The controller already holds a
-- per-node lock while it composes and records each send — the order existed and was thrown away at
-- the wire.
--
-- One counter per node, taken under that hold, one higher per send. Null is a machine sent nothing
-- since this existed, which is not the same as a machine sent nothing.
alter table node add column sequence bigint;