Fix latest PR review findings

- avoid git reset when repository has no HEAD\n- use React Query isLoading for checkpoint diff spinner\n- remove unreachable provider manager guard\n- add no-HEAD restore regression test\n\nCo-authored-by: codex <codex@users.noreply.github.com>
832eb42ad6Julius Marminge committed on 2/18/2026, 8:17:37 PMparentb1f6e72
4 files changedLine totals unavailable