On the web, an edit you make in the canvas panel while a reply is still being written is no longer lost. Press Enter in the canvas edit box, or pick a quick action, and the edit joins the chat's message queue as a row of its own, named after the canvas and the lines it changes; it goes out as a normal message once the reply has finished. Press Ctrl+Enter (Cmd+Enter on a Mac), or Send now in the panel, to stop the reply and send the edit at once. Your own message box is left as it was. If the canvas changes after you queued an edit, the row tells you, and the edit applies to the latest version.