Function barrier_marker_fence_decision 

pub fn barrier_marker_fence_decision(
    facts: BarrierMarkerFenceFacts,
) -> BarrierMarkerFenceDecision

Require the metadata image and installed partition to name exactly the expected leader generation; see barrier_marker_fence_model for which refusal each mismatch gets.

The host maps the refusals to different wire codes, so every variant is pinned.