Well, it could be a batch editor, such as linux's sed, invoked from the command line, or with "computer use" the model could indeed potentially drive a real interactive editor.

Part of the problem though is that tools like Claude Code don't want to assume too much of the environment - that a specific editor is available, or even that it is running on a particular OS. The way it remains platform agnostic and not reliant on specific tools is by only having a dependency on Node.js, which provides file read/write support, so to implement an edit request the agent uses Node.js to read the file, itself implements the edit, then again uses Node.js to create the new updated file.