Google Flights booking options for a selected itinerary

Return the provider booking list (airline + OTAs) for a selected flight.

The provider list is rendered client-side, so this does a JS render of the Google Flights /booking page (slower/pricier than search). Each option has the provider name and price; the actual per-provider booking links open from the returned booking_url (Google exposes them only as JS actions, not stable URLs).

Returns an empty booking_options for an incomplete round-trip selection (one that has not chosen a return leg) — follow that offer's booking_url to pick a return first.