Validation: Resource property cannot set readOnly properties

Currently, if set a value for a readOnlyProperties, this will be silently ignored. We should have validation to enforce this validation.

Start by locating the Java validation path that processes readOnlyProperties and reproduce the case where a value is silently ignored. Trace how resource property assignments are checked, then verify that assigning a read-only property produces a validation failure rather than being accepted or ignored.

Written by the indexing model from the issue text.