Create a checkpoint before modifying this
Ask the agent to save the current working state first, usually as a commit, so you can easily return to it if the changes go badly.
Record a known-good state before risky changes, typically by committing current work or creating a branch, so the new work can be compared against it and undone cleanly. Some agent tools also offer their own checkpoints.
Saving your game before the boss fight. If it goes badly, you reload the save instead of starting the whole game over.
Agents can edit dozens of files in seconds. Without a checkpoint, undoing a bad attempt means untangling changes by hand, often mixed with your own work.
Created a checkpoint: I committed the current working state as Before sign-up form restructure. Starting the changes now.
Create a checkpoint before modifying this: commit the current working state with a clear message, then make the changes on a new branch.
Thinking the editor's undo button is enough. Undo often can't reverse changes spread across many files, made by terminal commands, or from an earlier session.