remake: earlier epochs' metadata read as the snapshot built it

A snapshot leaving out earlier epochs' metadata (`snapshot::left_out`) and a rejoining
node (`catchup::prepare`) read it from the document as it stands. It is never writable
through the store, and under a policy the rules take a change to it only from an
epoch's first; but with no policy, screening judges only an epoch's root, so a member's
own change could rewrite or remove an entry: a replay window narrowed or widened, a
translation or a clock changed, a strict remake's entry gone.

Now both read it at the epoch's snapshot change (`snapshot::as_built`), as
`verify_document` reads the epoch's own: a snapshot from its base's epoch's, a
rejoining node from the target's. Every earlier entry is a copy in that change, so what
was written there since doesn't count. The first epoch follows none and has none.

0 files changed, 0 insertions, 0 deletions