Any git error on a directory under the worktree root was classified orphan,
and orphan deletes the directory outright, so a transient failure reading the
source root became data loss on a plain `agentws prune --yes`.
- prove a backing repo gone by stat before calling a directory an orphan
- classify an unexplained git failure as keep, naming the error
- refuse to remove a worktree whose git state is unknown, even with --include-keep
- spell out that --include-keep discards uncommitted and in-progress work
unkin-agent
62aeaf063b