Vercel Queue Consumer Groups

A @vercel/queue producer and consumer built around the fact that Vercel Queues inverts the publish/consume race: the docs state the publish acknowledgment and consumer notification happen simultaneously, so a consumer may begin processing a message before send() returns and the near-universal send-then-write idiom is a guaranteed intermittent 404. The producer commits first, then publishes with an idempotencyKey and a deliberately short retentionSeconds, and documents the hazard at the exact line where it bites. The consumer is one handler in one consumer group, because multiple route files on the same topic create separate groups that each receive a copy of every message, which is fan-out dressed up as scaling. Since there is no dead-letter queue, it implements a real poison-message policy: permanent versus transient classification, a deliveryCount cap, and acknowledge-with-record inside the handler where the write can be awaited. Also covers deployment-ID topic partitioning, the 300s SDK versus 60s raw API visibility timeout split, and the absence of FIFO ordering.