Release v19.38.2

Added

• Chronicle records which version of an event type's migration definitions produced each generation added by the backfill, and keeps every version of those definitions instead of replacing them (part of #4189)

Changed

• Register a new generation only after every Chronicle server in a cluster has been upgraded to this release. A server on an older release can still overwrite stored content during the upgrade. See the migration guide (part of #4189)

Fixed

• Registering a new generation of an event type no longer overwrites stored event content. The backfill only adds the generations an event is missing, migrating from the generation the event was appended in, or from the highest stored generation when that is unknown. It never writes over a redaction or a revision made while it runs. The backfill still covers only the default namespace's event log (#4709)