Function policy_on_class 

pub fn policy_on_class(
    policy: &Policy,
    settings_class: Option<&str>,
    class: &ClassInfo,
) -> Result<(Policy, BTreeMap<String, String>), HwError>

2026-09-30: policy with the class-decided settings re-read from class, unless class is the settings_class the policy was stated for; the changed keys are returned for the report. A class that does not state one is an error either way.