The Orphaned Goods
A merchant received orders from customers. Sometimes the orders couldn't be fulfilled: the item was discontinued, the customer's payment failed, the address was impossible.
Rather than let these orders clog the fulfillment queue, the merchant routed them to a separate ledger.
Each day, a clerk reviewed the ledger. Some orders could be saved — a corrected address, a substitute item. Others were cancelled cleanly.
The main operation never stalled. Problems had their own stream.