Delegated interrupt

[Niizuki]

Tl;dr;
Implement reverse control of train from stations by pushing interrupts on trains in service mode.

What?
Expand the already powerful system of interrupts. Allow a new type of interrupt for a train, "service mode". When in such a mode, a the train waits for a signal from s station. The station itself is set up with its own interrupt setting, and when conditions are fulfilled, it finds a free train in service mode, possibly from a specified group, and pushed result of the interrupt on the train.

Why?
Current interrupts are great, but there is an issue which seems to not be solvable, which is that while a train might be interrupted by signal from a resource source station, there is no way to check if unload station is currently available. This leads to trains ferrying resources too targets which are unable to handle them. By implementing this upgrade, player could use trains in a way where the stations which are starving can order a train to service them.