Function cache_is_stale 

pub fn cache_is_stale(meta: &CatalogCacheMeta, max_age: Duration) -> bool

True when the cache metadata is older than max_age.

fetched_at is parsed as RFC 3339 via chrono; an unparseable timestamp is treated as stale (the caller refetches rather than trusting a broken record). A timestamp in the future is not stale.