Function load 

pub fn load(
    layout: &RepoLayout,
    tree_hash: &Hash,
    expected_filter_hash: &Hash,
) -> Result<Option<(SparseManifest, SparseProof)>, CacheError>

Load a cached delivery for (tree_hash, filter_hash). Returns Ok(None) for a fresh repo / cache miss; Err(_) only for I/O or wire failures.

The function does not re-verify the bitmap-root against the bytes — that’s the verifier’s job. It only enforces that the cached filter hash matches the caller’s expected hash, so a stale cache for a different filter doesn’t get silently returned.

Errors

• CacheError::Io — I/O failure other than “not found”.
• CacheError::Wire — the cache file exists but is malformed.
• CacheError::FilterMismatch — cache exists for the tree but for a different filter.