Function evaluate_guard 

pub fn evaluate_guard(
    when: &WhenGuard,
    state: &GuardState,
) -> Result<bool, DispatchError>

Evaluate a guard’s truth value directly (R2 — guarded-skip). Does not special-case the R1 repair shape; callers that need to distinguish repair-fold from a plain on_failure skip should use classify_conditional_step instead.