Closes#3522. When --respect-staged is passed the git add loop is skipped
entirely so per-hunk staging from git add -p is preserved. Default behavior
(full re-stage) is unchanged. The #3061 pathspec invariant holds under both
modes. Nothing-staged within scope returns { committed: false, reason:
'nothing staged' } without error.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
