Plan an agent's part in a live column split

Your users table has one full_name column, and product needs first_name and last_name instead. The table has 40 million rows on a busy Postgres database, and the change has to happen with no downtime. You want an AI agent to do as much of the work as is safe.

How do you split the job? Decide which steps the agent does, which you keep, and where a person signs off before the next step runs.