The §11.6 files slice relies on the orphan sweeper covering the new `files/groups/<group_id>/...` subtree "for free" via its recursive walk of `<root>/files/`, with no sweeper code change. Lock that guarantee with an explicit test so a future sweeper refactor can't silently drop group-shared tmp files. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>