v4.7.7 — Split the harvest's memory write from its Working Memory sync

Harvests now bank to the store quietly. Rebuilding the Working Memory block
is a separate command, run only at boundaries where no agent whose value is
independent judgement is still to spawn.

Before this, saving a HANDOFF also rewrote the block every agent loads at
spawn, so harvesting early put the builders' conclusions into the reviewers'
context and harvesting late risked losing the HANDOFFs to a dead session.

Also: the block is a view of the store, corrected on the record and
re-projected rather than edited in place; the spawn-time cleanup no longer
deletes records; both timestamp columns are required rather than defaulted
to a second format; the ordering tiebreak is asserted in the statement the
engine is handed, so its protection no longer depends on the query plan; and
reviewer open questions cannot reach merge without a recorded disposition.