World contract boundary
World owns typed, versioned referents and vocabulary: WorldObject, kind and
facet/relation definitions, aliases, identity-resolution decisions, and
merge/split lineage. It does not own observations, claims, beliefs, or the
truth of values about a referent; those remain Epistemics-owned evidence.
Cross-owner references are typed semantic references. They do not create
cross-owner foreign keys, joins, writes, or a generic Entity(any) API.