Kibana saved-object migration behavior during major version rolling upgrades

When performing a rolling upgrade of Kibana instances behind a load balancer, the system triggers an automated saved-object migration on the .kibana system indices upon the first instance's startup. While Elasticsearch supports rolling minor-version upgrades, Kibana requires a strict version match between the application and the cluster to function.

The primary concern involves the persistence of custom objects—such as dashboards, index patterns, and alerting rules—when moving across major version boundaries. If a specific object type is deprecated or removed in the target version rather than transformed, the migration process may fail or result in data loss within the Kibana state.

How does Kibana handle saved objects that have been completely removed in the newer major version during a rolling cutover? Is there a mechanism to prevent the first instance from initiating an irreversible migration before the compatibility of all custom objects is validated?