To be super pedantic, wouldn’t the interface to a shell itself be a Command Line Interface? ;)

that’s the ambiguity that I think is tripping the discussion up a little. Also the idea of a CLI/Shell/Terminal is also quite coupled to a system, rather than services. Hence the whole ‘web service’ hope to normalise remote APIs that if you squint hard enough become ‘curl’ on the command line

But the point is none of that is intrinsic or interesting to the underlying idea, it’s just of annoying practical relevance to interfacing with APIs today