How does a fixed route load and unload at each stop?

A wagon uses one shared cargo hold and checks each stop in travel order; it does not reserve source A's cargo exclusively for destination B. The route must pass the facility's green entrance arrow, and the station must allow the cargo item. Ordinary sources primarily load unreserved surplus above their plan. Planned receivers unload according to their current stored shortage; chests and material piles accept matching goods if space exists. A full wagon cannot load more. Chests and piles on a route choose loading or unloading; the home station must permit both. Return travel visits stops in reverse order, using whatever cargo remains.