By "planning", I actually meant "thought of one time". So, I did it.

The endpoint verifies that the destination specified by the POST is in my project folder. If it points at an existing file, it creates a version. It does not overwrite.

I added a CLI, watchFile, that blocks Claude until the file shows up.

And made a skill that tells Claude to respond nicely to "Make an interactive document that...".

Claude Code has basically made software functionality, "Your wishes come true".