Zero-reply threads older than the threshold below are tagged noindex, follow until they earn a reply, so the thin tail stops dragging on sitewide quality. Links out of the thread are still followed. Report emits an observe-only X-Advally-Robots-Preview header that no crawler acts on, so you can measure exactly which threads would be affected before committing. Enforce emits the real X-Robots-Tag. Off disables the engine.