Background chats see their own canvas
A chat drawing on its canvas in the background now sees that canvas each turn, so it builds on the board instead of starting blind.
Every chat has its own canvas, and each turn Bandicot shows the model what is on it. That note was only added for the chat open in the window, so a chat working in the background could edit its board without seeing it.
Now each chat sees its own canvas, wherever it runs.