Function build_commit_record 

pub fn build_commit_record(
    identity: &ProductIdentity,
    source: DistributionSource,
    entry_id: &str,
    product: &[u8],
    archive: &[u8],
    provenance: &[u8],
) -> Result<Vec<u8>, ExactCacheError>

Build a canonical commit record for an immutable cache transaction.

entry_id must be a freshly allocated, immutable transaction directory. Native callers normally use ExactProductCache::publish, which allocates it. WebAssembly hosts can generate 16 random bytes, encode them as lower-case hexadecimal, store the three byte objects under that identifier, and then atomically replace their commit marker with the returned bytes.