Function handle_close_worker 

pub(crate) fn handle_close_worker(
    workspace: &Arc<Workspace>,
    project_key: &ProjectKey,
    label: &str,
)

Handle a Command::CloseWorker (a view’s per-row X-button): tear the worker down via teardown_worker. Does NOT touch the git worktree - that’s the agents__despawn path’s job; the X-button’s behavior is intentionally unchanged.