Return enough information to merge external itineraries into the OTP trip search #6976
Description
Is your feature request related to a problem? Please describe.
With the new paging feature in OTP, there is insufficient information to merge in other itineraries. This makes it difficult to perform multiple trip searches or merge results from planners other than OTP. The main problem is that the client does not know which time window is returned. OTP may crop the requested time window, and the start and end of the returned window are not provided. OTP also scales the search window up if no results are found. If no results are returned, it becomes even harder (impossible) to determine the time window of the result.
Goal / high-level use case
Advanced clients may want to merge several trip searches from OTP or other planners together.
Describe the solution you'd like
A simple solution is to provide the client with more information, making it possible to merge results and maintain the natural sorting order—avoiding new itineraries popping up in between existing ones.
Describe alternatives you've considered
OTP should be able to run multiple requests, feed the results into the itinerary filters, and produce one list of results. In particular, there is currently no good way to mix direct FLEX with regular transit.
Additional context
This problem was reported by Ruter: https://entur.slack.com/archives/CHL39FFAS/p1757429404340369 (private)