AWS S3 by itself is made up of 300 microservices. Absolutely no developer at AWS knows how every line of code was written.

The scalability requirements are part of the “non functional requirements”. I know that the vibe coded internal admin website will never be used by more than a dozen people just like I know the ETL implementation can scale to the required number of transactions because I actually tested it for that scalability.

In fact, the one I gave to the client was my second attempt because my first one fell flat on its face when I ran it at the required scale

I'm not talking about scalability requirements. I'm talking about the different workflows that 10 million people will come up with when they use a program that won't exist in any requirements docs.

Do you think that AI coded implementations just magically get done witkoug requirements?

You're not understanding what I'm saying. If you go tell your agents to add this new feature to an app, and you do it by writing up a new requirements doc. If you don't review the code, they will change a million different "implementation details" in order to add the new feature that will break workflows that aren't specified anywhere.

The code is the spec. No natural language specification will ever full cover every behavior you care about in practice. No test suite will either.

If you don't know this, you haven't maintained non-trivial software.

And have you never seen what a overzealous developer can do and wreck havoc on an existing code base without a testing harness? Let a developer lose with something like Resharper which has existed since at least the mid 2000’s

If your test don’t cover your use cases, you are just as much in danger from a new developer. It’s an issue with your testing methodology in either case.

And there is also plan mode that you should be reviewing

Of course they can. Those kinds of developers cause problems constantly. It's one of the biggest reasons we have code reviews. Automated tests help too.

But even with all of that we still have bugs and broken workflows. Now take that human and remove most of their ability to reason about how code changes affect non-local functionality and make them type 1000x faster. And don't have anyone review their code.

The code is the spec, someone needs to be reviewing it.