How do I manage included files in a new chat by default?

It’s not clear to me how the context selection works when I start a new chat window.

It always seems to provide some files already in there and then I have to hit backspace several times since it inevitably always gets it wrong.

Is there a hotkey that will allow me to do something like Command+Backspace so it removes all the contacts? And if not, is there a better way to set this up?