Blocker Description
Whenever we support ZK-to-KRaft upgrade we must confirm that we can still read messages with an older message format. We can no longer write such messages as of IBP 3.0 (which is the minimum supported with KRaft), but we must still support reading such messages with KRaft. Therefore, the only way to test this would be to write the messages with a non-KRaft cluster, upgrade to KRaft, and then confirm we can read those messages.