Function write_cached_layout 

fn write_cached_layout(
    cache_dir: Option<&Path>,
    address: Address,
    name: &str,
    layout: &StorageLayout,
)

Persists a resolved layout so later runs can skip the fetch and the compile.

The entry is written to a temporary file and renamed into place, so parallel tests writing the same address cannot leave a reader with a half-written file.