What is the best tool/setup to use an LLM to actively work on a text document real time, like cursor.ai does for code? 

The workflow I’d like is closer to “colleague commenting + making suggestions in your google docs” than copy/pasting a bunch of stuff back and forth.

https://lex.page/ 

i haven't used it myself so can't speak to its quality, but believe that is what it's going for

if you do use it, please let me know how well it works!

(disclaimer: my wife's firm invested in it)

+1 to lex for editing features with decent llm but AI not comparable to solomode across notebooklm or openai canvas