Third feature-detected rail on the detail page. When the backend returns similar_audiobooks (server-side embedding similarity, ranked top-N), the rail mounts above Also-by-author and In-series, with the subtitle 'Based on listening patterns' to give the recommendation source a little provenance. Frontend has no embedding logic — purely a display path that lights up the moment the API exposes the field. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>