Function build_checkpoint_with_previous 

pub fn build_checkpoint_with_previous(
    checkpoint_seq: u64,
    batch_start_seq: u64,
    batch_end_seq: u64,
    receipt_canonical_bytes_batch: &[Vec<u8>],
    keypair: &Keypair,
    previous_checkpoint: Option<&KernelCheckpoint>,
    prior_chain_leaf_hashes: &[Hash],
) -> Result<KernelCheckpoint, CheckpointError>

Build a signed kernel checkpoint that explicitly links to the previous checkpoint when provided.

prior_chain_leaf_hashes must hold the chain leaf of every prior checkpoint in sequence order (see checkpoint_chain_leaf_hash); the new body then carries a chain_root extending them, and the leaves are cross-checked against the predecessor’s own commitment when it has one. An empty slice is valid only with no previous checkpoint.