Is it safe with uncommitted work?

Yes. Sync operations never merge or rebase your working copies. They fetch, create missing worktrees, fast-forward eligible existing worktrees, and prune only when the safety checks pass. Worktree removal refuses on dirty trees, unpushed commits, stashes, or in-progress operations (merge/rebase/cherry-pick/revert/bisect). Newly created branches are pushed with explicit --no-track so they don’t inherit origin/main as upstream by accident.