Twelve objects, four kinds, one chain

A haul passes through a marketplace, an agent, a payment route and a carrier, and each of those owns a different set of failures. Knowing which party owns a stage is most of what makes a problem solvable, because a query sent to the wrong party costs a cycle.

Payment routes sit outside the six-stage rail on purpose: they move money before a parcel exists, which is why a transfer cost is easy to forget when the haul is totalled later.