Safely undo or roll back changes: discard working-tree edits, unstage files, undo the last commit(s), or recover a commit that looks lost

Documented steps

1. To discard uncommitted edits in the working tree and restore a file to the index's version, run `git restore <path>` (or `git restore .` for the current directory, `git restore :/` for the whole repo). Add `--source=<commit>` to instead restore from a specific commit/branch/tag rather than the index.
2. To unstage a file (move it from the index back to unstaged, without touching the working tree), run `git restore --staged <path>` — this is the same effect as `git reset <path>` (for a specific path). Combine `--source=HEAD --staged --worktree <path>` to reset both index and working tree together (equivalent to old-style `git checkout <path>`).
3. To undo the last commit but keep its changes staged, run `git reset --soft HEAD^` (or `HEAD~1`) — this moves HEAD back one commit while leaving the index and working tree files untouched, so you can immediately `git commit` again (useful for squashing recent commits or rewording).
4. To undo the last commit and unstage its changes but keep them in the working tree, run `git reset --mixed HEAD^` (`--mixed` is the default mode if no flag is given, so plain `git reset HEAD^` does this) — it updates the index to match the new HEAD but leaves working-tree files unchanged.
5. To completely discard the last commit and all its changes, run `git reset --hard HEAD^` — this overwrites working-tree files and the index to match the target commit, removing tracked changes not in that commit; it can also overwrite untracked files, so make sure nothing unsaved needs keeping first.
6. Before any reset, note that Git automatically records the pre-reset tip in `ORIG_HEAD`, so if `--hard` (or any reset) turns out to be wrong, you can immediately recover with `git reset --hard ORIG_HEAD`.
7. For older or more complex loss (e.g. `ORIG_HEAD` already overwritten, or a commit lost across multiple operations), run `git reflog` (or `git reflog show <branch>`) to list HEAD's history — each entry like `HEAD@{2}` records a prior position — identify the lost commit's SHA and recover it with `git reset --hard <sha>` or `git branch <newbranch> <sha>` to avoid touching your current branch.
8. Verify the recovered state with `git status` and `git log` before continuing work.