backup_revision_stale· reason_code· applies to device_recovery, state_resolution`ak.schema.key_backup.v1.source_commit_ref.realm_commit_id` does not resolve to an accepted RealmCommit on the principal control stream, or `device_generation_ref` does not equal the active `current_device_generation_ref`. A later RealmCommit on the same stream does not by itself make the envelope stale. Receivers MUST refuse to use the envelope as the primary recovery source. See zh/identity/key-management.md §7.6.