The Supply Chain AI is based on how real world companies do it. While there is supply on demand companies such as UPS and FedEx. There are transportation companies that have supply built into their networks. For example, companies can rent rail cars and place goods on them, even before those goods have buyers. In this case, the rail car is rented until all the goods are removed. Almost like a warehouse on wheels. Similarly, gas producers will have supply in the pipelines to meet customer demands, they only turn on or turn off gas pumps as supply in some fuel diminishes.
This technique is called caching, and this means that the game can simulate the cache mathematically without having to simulate it. It means that supply yards don't have to keep tanks and tanks of supply, rather they just have to have source supplies meet ultimate demands.
This means the AI will identify the rate that units can be added to the system at all of the mining sites, and as units are used, the units can be added from the mineral sites into the system to satisfy the temporary shortfall. It means I do not have to simulate the infrastructure to do this, instead it can be just a simple calculation.