Keep pre-2.7 keep-warm records warm across the upgrade (#677)
Merged
AN
7h ago+248+248+012345678901234567890123456789-11-11-01234567890123456789
Keep pre-2.7 keep-warm records warm across the upgrade (#677). Worker delivery rebased onto main; see the commit messages.
Summary by cubic
Keeps cache-keep sessions saved by pre-2.7 versions warm after upgrading to 2.7 instead of dropping them at restore. The limit of 24 warms without a real request now counts from the restart for legacy records, and records that still require a real request are dropped as before.