remake: leave out earlier epochs' metadata past the replay window

Every snapshot carried the metadata of all earlier epochs (`_continuum/epochs`)
forward, so it grew by an entry, a clock per actor among it, with every remake. Only a
rejoining node reads an earlier entry: a node on epoch P reads P+1's (its clock, when
it was proposed, its replay window) and every one up to the swarm's epoch (kind,
translation, whether it was strict). It replays only while P+1's replay window covers
it; beyond, its writes are quarantined whatever the entries say.

So a snapshot now leaves out the generations older than the oldest whose replay window
still covers a node on the epoch before it (`snapshot::left_out`), judged by the
remake's `proposedAt`: the same on every node, and earlier than any rejoining node's
clock, so nothing a node can still replay through goes. Metadata that doesn't read
stays, with all after it.

A strict remake's metadata stays for good: by it a rejoining node, however far behind,
tells a strict remake of a swarm strict already (`catchup::prepare`, which reads the
generations it finds). There is at most one, short of such a remake. No new key and no
change to the rejoin: a node beyond the window that finds some entries and not others
quarantines with "cannot translate" rather than "outside the replay window".

0 files changed, 0 insertions, 0 deletions