Multi-turn tool-use scenario.
Tools involved: VehicleControlAPI

User requests (one per turn):
user: I'm setting off on a road trip and my departure point is sunny San Francisco. Could you determine the distance to help me plan my fuel stops on the way?
user: My destination is Rivermist.
user: Before embarking on this journey, please top up my vehicle to end with 50 gallons of fuel.
user: Please start the engine to prepare for our travel. Ensure that the car is locked and everything is secure for a seamless start.

Expected function call sequence:
VehicleControlAPI.fillFuelTank
VehicleControlAPI.startEngine
VehicleControlAPI.get_zipcode_based_on_city
VehicleControlAPI.estimate_distance