The builder
History and undo
Nothing the agent does is a one-way door. Edits are revisioned, and you can step back through yours and its.
Undo
Direct edits on the canvas undo the way you would expect. Agent runs are recorded as their own entries, so reverting one does not unpick the manual edits you made around it.
Revisions
Every page, section and site carries an updated_at revision. Writes take the revision they are editing, and a write against a stale revision is refused rather than applied on top of someone else's change.
Changes appear as they happen
When an agent writes to a site you have open — whether that is the built-in panel or an MCP client in another window — the canvas reflects it without a reload.