4be32d411c
Applying a directory-sync effect that would demote the org's last Owner (a group remap, or a provision) previously threw and 500'd the settings save. Now rbac.setUserRole reports code:"last_owner" and applyEffect skips just that member (they keep Owner) while the rest of the batch applies. Adds the machine-readable RoleAssignmentResult.code to the plugin contract so callers can tell the last-owner guard apart from a real failure.