Function resolve_correlation_id 

pub fn resolve_correlation_id(headers: &HeaderMap, request_id: &str) -> String

Resolve the request’s business correlation ID (DW-093): a valid inbound X-Correlation-Id verbatim, else the already-resolved request_id (so every request carries a non-empty correlation handle for the journey/funnel query even when the client did not send one). The validity gate mirrors valid_inbound_request_id (printable ASCII, at most 128 bytes) so hostile IDs cannot smuggle control characters into the analytics store.