Initiate a train search and stream normalised solutions back as Server-Sent Events. Each data: event is a JSON-encoded train solution object. The stream ends with event: done.

The party is passengers (anonymous seat counts per age band) plus travelers (selected people by userId). Each named traveler's own saved railcard — the signed-in traveler's or a colleague's — is applied to that traveler's seat and carried through the inbound search, fare search, and fare build; book the colleague with passengers[].colleagueId to apply it on the booking. Anonymous seats carry no railcard. Guests cannot name travelers (422).