Constant SPLUNK_PK_METADATA_ORDER_KEY 

pub const SPLUNK_PK_METADATA_ORDER_KEY: &str = "splunk_pk_metadata_order";

QueryContext extension key the Splunk HEC handler sets (to "true") on its identity path to request metadata-first primary-key ordering at table creation. It is absent for user-supplied pipelines, so their primary-key order is left untouched.