MessageQueueStats is a point-in-time snapshot of how many messages a single
queue currently holds. Surfaces only the two signals that drive the
parallelism decision: messages ready to be picked up and messages already in
flight. The UI can sum them for a "current load" display.
- queueNameStable queue name, suitable for display (e.g. "async-jobs", "dlq").
- clientTypeThe kind of backend serving this queue (e.g. "postgres", "aws_sqs").
- visibleMessages ready to be received.
- inFlightMessages received but not yet acked or deleted.