Function load_local_catalog_metadata 

pub(super) fn load_local_catalog_metadata(
    path: &Path,
) -> Result<Option<CatalogMetadata>>

Tries to load the local catalog metadata file if it already exists.

This is the refresh-path entry point for on-disk metadata. It performs a single open attempt and only validates the file when the open succeeds, which avoids a separate existence check and the TOCTOU window that comes with it.

Returns Ok(None) when the file is missing, which is the normal cold-start case for a first refresh. Any other filesystem, parse, or validation failure is returned as an error so callers can surface the problem.