Mentor a new engineer who hands everything to AI

You mentor an engineer in their first year. They ship fast by having an agent write almost everything, including changes to the service's job scheduler and its data-access layer, the 2 parts the team most needs them to learn. Their PRs pass review. Last week, during an incident in the scheduler, they could not explain how a failed job gets retried.

What do you tell them to hand to the agent and what to write themselves, and how will you both know it is working?