Server should clear unknown fields on READ operations #1205

An old server replica doing Read-Modify-Write should drop unknown fields on read and serve the reduced object

• WHY: After a rollback the unknown field is only understood by the rollback-FROM version. Keeping it forever means the server cannot validate, and it becomes an invisible bomb activated at the next roll forward since it's from an stale and untrusted version. Dropping on read makes the loss explicit.

• Ref: K8s prunes unknown fields at the API boundary for Custom Resource at https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#field-pruning

Crossref #954 (comment)