series_chain_broken· reason_code· applies to schema_validation, state_resolution, device_recoveryak.schema.key_backup.v1 envelope chain failed verification: a `supersedes_digest` does not match the canonical_json digest of its predecessor, or a non-genesis envelope is missing a predecessor accessible to the caller. See zh/identity/key-management.md §7.6 and zh/crypto-media/device-lifecycle.md §12 / §12.1.