It does take a lot of work not to break things. That's why "move fast and break things" are traditionally closely coupled: it's hard to avoid breaking things without slowing down.

But why would responsible AI users -- actual engineers using it to accelerate grunt work, not vibe coders -- not use the AI tooling to increase their capacity to do all of the work it takes to avoid breaking things while still moving fast, relatively speaking?

Testing a new incremental feature against the entire extant codebase, not just the bits of it that they had the bandwidth to tackle within the deadline, seems like exactly the sort of thing well-disciplined engineering teams would use AI to do.