Most AI writing help starts with an empty box. You paste in the message, explain who the person is, explain what happened last week, and then ask for a reply. By the time you've typed all that, you could have written the reply yourself.
The thread already has that context. Who said what, what was promised, how the other person writes. A reply that ignores it reads generic, even when the grammar is perfect.
That's the idea behind Grais, an AI communication assistant that drafts from the open thread. It's a Chrome extension. It reads the conversation you have open in the browser and drafts a reply you can check and edit before sending. Nothing goes out on its own.
It won't help much with a two-line "sounds good, see you then". For those, just type it.