If you haven't read the first blog post it's pretty good at explaining the concepts.

https://blog.buenzli.dev/announcing-development-on-flirt/

The demo is particularly good if you can get past ( by the authors own admission ) slow typing speed.

As with everything these days I can see this being even more useful in reviewing agent code.

For example if an agent has spat out a bunch of code that I've reviewed and then I've asked it to make changes, I definitely do not want to review all that code again in the same diff later.