But that's not what this is about:

> For many projects, maybe ~80% of the thinking about how the software should work happens after some version of the software exists and is being used to do meaningful work.

Some version of the software exists and now that's your spec. If you don't have a formal copy of that and rigorous testing against that spec, you're gonna get mutations that change unintended things, not just improvements.

Users are generally ok with - or at least understanding of - intentional changes, but now people are talking about no-code-reading workflows, where you just let the agents rewrite stuff on the fly to build new things until all the tests pass again. The in-code tests and the expectations/assumptions about the product that your users have are likely wildly different - they always have been, and there's nothing inherent about LLM-generated code or about code test coverage percentages that change this.