In disagg., WiredTiger uses checkpoint_meta to specify the checkpoint metadata for a database-wide checkpoint, and it contains all information that a follower needs to pick up the given checkpoint. This is in a way analogous to how checkpoint cookies specifies the metadata of table checkpoints.

To make checkpoint_meta more extensible, we should add two more fields to it:

• version = the version of the data structure.
• compatibility_version = the minimum version of the reader that can use the checkpoint_meta to safely pick up a checkpoint, just by ignoring any unknown fields.