HA 2026.8 rejects ANY non-numeric native_value on a unit-bearing snmp sensor at entity ADD (host down at boot renders ''/'unknown'/'None' as strings) — unit-bearing adds crash and the entity vanishes until manual reload. Raw layer now carries no unit (validation off); semantic template layer carries unit + device_class under the original unique_ids so entity_ids, dashboards, and automations are unchanged. https://projects.knownelement.com/issues/344#note-3916