Function create_shadow_worktree_named 

pub fn create_shadow_worktree_named(
    repo_root: &Path,
    worktree_name: &str,
) -> Result<PathBuf, WorktreeError>

Create an isolated git worktree with an explicit name. Callers that share the .worktrees/ namespace with other features (e.g. apply staging vs. mutation testing) MUST use a distinguishing prefix so lifecycle pruning never reaps another feature’s live worktree.