Allow Trade Contracts to Be Fulfilled Across Multiple Cargo Ship Voyages

Currently, trade contracts directly couple the exchange ratio with physical cargo transportation. This becomes awkward when a small amount of a high-value manufactured product is exchanged for a large amount of raw material.
For example:
1 advanced product → 10 raw materials
The exchange ratio may make economic sense, but the corresponding cargo volumes do not. A small amount of exports can represent several shiploads of imports, while expensive export goods may sit unnecessarily in cargo modules waiting for later contract cycles.
I suggest separating contract settlement from physical transportation.
When export goods are delivered, they should create a persistent entitlement to the contracted import product.
For example:
10 Electronics exported
→ 100 Iron Ore available for import
The Iron Ore could then be collected over multiple voyages:
Voyage 1: 40
Voyage 2: 40
Voyage 3: 20
The remaining amount would simply be stored in the contract.
This would NOT require money or a global market. CoI could keep its barter economy and existing contract ratios; the game would only remember how much import product is still owed.
Ideally, different ships could handle exports and imports. This would also make future transport types more useful: small-capacity transport could export high-value goods, while cargo ships import bulk resources.
In short:
Current: Export ↔ Import must be coupled to the transport cycle.
Suggested: Export → persistent contract entitlement → Import can be transported later.