A target/ here is eight to twenty gigabytes and there is one per worktree, so a machine fills during a link and the failure reads as a compiler bug. disk reports every one with what it costs and what it belongs to; --clean removes only those whose worktree is gone, and never one touched in the last hour. Change-Id: I51ecb8a7a4cb9c3b7a1debd459c4cc924690364a