> Perhaps the language is too small a vantage point to really get into what’s happening when debugging

A little bit. The big thing that others are missing is that it's basically impossible for a PL to accomplish this. Antithesis is basically recording all the state including I/O, network I/O, all RNGS (including the OS) and the big one which everyone has trouble with which is time. So basically you don't need to set up your code and how it interfaces with its environment to be deterministic - you can run within a deterministic container instead which flips the problem on its head and makes it much easier. I'm sure there are tradeoffs. A noteable one is how expensive and slow this approach is vs making your code deterministic. But given how basically no one bothers to make their code deterministic and this is a drop-in solution for scenarios like that, it's really worth it. Additionally, unlike approaches like rr which offer similar capabilities, this is even more generic & not dependent on adding support for every OS interface (e.g. rr doesn't support io_uring yet but I believe antithesis would since it's running at the VM level)