The wall grows as you drop sessions onto it
Turn on the wall and it starts with your open session. Drag more in and the layout reshapes from one to as many as fit; a full wall offers a swap.
Turning on the wall now starts from the session you are in. Drag another session from the sidebar onto it and the tiles reshape smoothly, from one to two to three, up to as many as the window can show well.
When the wall is full, dropping one more offers to swap it for the quietest tile instead of losing anything. Drag a tile by its header to reorder, or drag it off the wall; it keeps running in the background.
Everything works from the keyboard too: Option with the arrows moves a tile, Delete takes it off the wall, and each change is read out for screen readers. With reduced motion on, the layout changes without animation.