Name ownership
Every shared dataset needs a producer, known consumers and an escalation path. A schema without operating ownership is documentation, not a contract.
Version behavior, not only fields
Nullability, freshness, ordering and deletion semantics can break consumers without changing a column name. Put those expectations beside the schema.
Observe the agreement
Measure conformance, freshness and failed deliveries. A contract becomes useful when violations are visible before they silently corrupt downstream decisions.