What do you do? You provide guidance, support and tooling so they can write better tests and code. You supervise and help them meet the standard. It is the same with AI agents (including the challenge of how to carry that knowledge around and transfer it). You are responsible.
You are also responsible for the understanding part: know what is being worked on, glance at changes, inspect the outcomes, cross-check specifications, tests, product requirements. The 'moving too quickly' idea is the other side of the same coin; it is your responsibility to keep track of things and decide what's worth intervention. The exact same thing happens in a project where you have ten developers (or 200) working together — you cannot possibly read all of the code they write.
Seeing all of these as downsides is a choice.
When I do the same with an LLM, I'm just repeating the same guidance over and over again out of frustration just to get something done.
Comparing an LLM to a junior engineer is frankly a disgrace.
For that you need to actually read the code and it's somehow in odds with the whole vibecode idea.
Plus it won't give you the 10x boost the management expects. Only not looking at the code will.