The hourly buildkit-cache-prune.timer runs prune.sh against the explicitly named Worldtree, Skaldsong and Soong builders. Each running builder prunes unused cache toward 10 GiB (--keep-storage 10240). This is periodic reclamation, not a hard disk quota; in-use cache and growth between runs can exceed the target. Missing and stopped builders are skipped and are never started by the timer. Build caches are regenerable, but subsequent builds can take longer.

On 2026-09-10, Skaldsong reclaimed 10.41 GB and Worldtree reported 74.89 GB reclaimed (BuildKit accounting). Worldtree was temporarily started for that initial prune, then returned to stopped. Soong remained stopped. Following cache pruning and the Gitea backup repair/cleanup, root usage fell from 84% to 51%, with 115 GiB available. Use filesystem df for actual capacity rather than summing cache reports and logical file sizes.

Checks: systemctl status buildkit-cache-prune.timer, journalctl -u buildkit-cache-prune.service, and df -h /.