In a similar vein, I want a text editor where pasting from an external source isn't allowed. If you try, it should instantly remove the pasted text. Copy-pasting from inside the document would still be allowed (it could detect this by keeping track of every string in the document that has been selected by the cursor and allowing pastes that match one of those strings).

It wouldn't work in every use case (what if you need to include a verbatim quote and don't want to make typos by manually typing it?), but it'd be useful when everything in the document should be your words and you want to remove the temptation to use LLMs.