I'll bite.

Claude code interacts with many system processes, files, etc, as well as external APIs. Processes audio via built in dictation. Manages a bunch of nasty auth. Etc etc.

What are the categories of features that wouldn't be exercised by this class of software?

Yeah, but a lot of hard work is done by those libraries. Interaction with external interfaces would go through the tools API, which I imagine would all use the same type of code that they could focus on fixing quickly.