Function rebuild_header_path 

async fn rebuild_header_path<State>(
    state: &State,
    root: u64,
    header: Header,
    head: u64,
    fetch_timeout: Duration,
) -> Result<HeaderProof, Error>
where
    State: AvailabilityDataSource<SeqTypes> + MerklizedStateDataSource<SeqTypes, BlockMerkleTree, { BlockMerkleTree::ARITY }>,

Prove header against root using the snapshot at head, when the state at root is pruned.

The result is verified against the commitment in header root.