Function store 

pub fn store(
    layout: &RepoLayout,
    tree_hash: &Hash,
    manifest: &SparseManifest,
    proof: &SparseProof,
) -> Result<(), CacheError>

Persist a verified manifest + proof to the cache. Idempotent: re-storing the same (tree_hash, manifest, proof) triple over-writes the existing bytes byte-for-byte.

Errors

Returns CacheError::Io for any underlying filesystem error. The missing parent directory is created first; if that or the write fails (typically permissions / disk full) the error is propagated.