After a quarterly refresh of an internal knowledge base, an engineering-support assistant began recommending a deprecated deployment procedure. Investigation shows the refresh added new runbook versions but the old versions' chunks are still in the index, and chunks carry no version or effective-date metadata. Which design change prevents this class of failure?

Answer: B — Use stable document IDs with version metadata, and rebuild each index version atomically so superseded chunks go

Stale answers come from stale chunks that nothing removed, and from missing metadata that would let retrieval tell versions apart. Stable IDs, version metadata and atomic, validated rebuilds handle supersession and deletion. (a) asks the model to guess currency from wording. (c) tunes ranking but the stale chunks remain. (d) adds a re-embedding change without fixing supersession; old and new procedures may read almost identically.