A maintenance team at Cedar Transit needs several small data helpers before its next release. The helpers cover work you've already practiced: integer boundaries, strings, collection lookup, stable order, and independent copies. Each function has a different contract. Read the requested output shape before choosing an operation, because sorted output and first-seen output are different results. The inputs here are fresh and use fictional queues, stock movements, and build labels. There is no shared state between tasks. Your answer should handle an empty collection and a repeated identifier wherever the contract permits them. Use the hints only after you've tried a concrete example by hand.