Disaggregated checkpoint metadata may be received without database_size. We currently treat this field as optional to avoid failures when size information is missing. Once checkpoint size support is fully established, this fallback handling should be removed and database_size be made mandatory.

Scope:

• Remove:
  • has_database_size field from WT_DISAGG_CHECKPOINT_META
  • WT_ERR_NOTFOUND_OK fallback in __disagg_pick_up_checkpoint_meta  
  • Conditional check in __disagg_update_checkpoint_meta
  • FIXME
• Ensure database_size is non-optional in checkpoint metadata