git diff HEAD backups break when an external diff tool is set

If the user's git config sets diff.external (e.g. difftastic), git diff HEAD > backup.patch writes side-by-side display output, not a patch, and git apply later fails with 'No valid patches in input'. Always use git diff --no-ext-diff HEAD for any diff you intend to apply or parse. Also re-check git status/git log right before committing a planned split: another session may have committed and pushed the same changes while you waited for approval, and splitting then needs a force push.