We definitely were combining the rewrite with the opportunity to lay foundation for a more performant architecture, for instance index management and indexing autosharding could be resourced together in the new world with slightly different semantics in the apis. So in general if the traces disagree, we can count on the new version being correct (unless the spec was covered by a TLA spec)!

At the moment the reverse is true though, the simulator and what we've captured as ground truth for the desired design has been refined enough in tests and specs that the code is often the one implicated, and most of the bugs have been in code related to caching correctness and are only exposed through soak testing.

In opposition to Anthropic/Bun, we mostly used a hands-on approach to the rewrite and took the opportunity to capture the original design of Antfly into specs and any missing tests one subsystem at a time so we didn't strive to be as hands-off as "let Claude hill-climb on the tests". Especially since the system as a whole is far more dynamic and depends more on scalability, distributed systems stuff than Bun required!