Ah that's a bummer. You can still add threads as context, but that you cannot use slash commands there, so the only way to add them or other stuff in the context is to click buttons with the mouse. It would be nice if at least slash commands were working there.
edit: actually it is still possible to include text threads in there
It actually seems to work for me. I have an active text thread and it was added automatically to my inline prompt in the file. There was this box on the bottom of the inline text box. I think I had to click it the first time to include the context, but the subsequent times it was included by default.
edit: actually it is still possible to include text threads in there