structure_depth_exceeded· reason_code· applies to encoding, schema_validationA canonical JSON or deterministic CBOR structure exceeds the v1 maximum nesting depth of 64 (objects and arrays combined, top-level container = depth 1). Receiver MUST reject (top-level schema_violation) before recursive descent can exhaust the stack, and MUST NOT truncate or partially parse. See zh/conformance/scalability-constraints.md section 2.