message: consistent upper bounds
diff: @@ -225,7 +225,7 @@ where
  // A block must carry a QC to its parent.
  checked_precondition_eq!(quorum_cert.certified_block_id(), parent_block.id());
  checked_precondition!(round > parent_block.round());
  - checked_precondition!(parent_block.height() < std::u64::MAX);
  + checked_precondition!(parent_block.height() < std::u64::MAX - 1);
  Block::new_internal(
  payload,
  parent_block.id(),
  