failed_precondition· code· HTTP 409· scope bothReducer state-machine or typed CAS precondition failed. A stale typed revision writes nothing and does not carry a generic current/current_result Problem extension; authorized current is obtained only through a separately registered read. Other failures may carry a registered reason_code in the {strand,space,morph}_not_active / _not_archived or {strand,space,morph,message,relation}_already_terminal families, or an object-specific reason such as space_parent_cycle. See zh/models/common-fields.md §5.1 and zh/sync/current-results.md §2.