Shared-ride matching

Design the shared-ride (carpool/pool) matching service that combines multiple riders going in similar directions into one vehicle in real time: a new request must be matched to an in-progress or forming trip within seconds such that the added detour for existing riders stays under a bound and total vehicle occupancy and routing stay feasible. 10k pool requests/second in dense metros. Cover candidate generation, the matching decision, and the detour/feasibility trade-off.