I do agree there should be a way to dismiss the editor when you are sure you want to compose the rest of the post on a different device or what have you.
Draft saving is always implicit and automatic, the only missing piece is explicitly dismissing the editor if you get halfway through replying to one topic, and decide you want to reply to a different topic, etc.
Something like that, not sure what the text would be, but the button would essentially reset the editor so you don’t have the draft following you around from topic to topic etc.