The engine has always accepted it — edge target, line of sight to the edge, open corridor only — but the client's EDGE_CARDS list never included illusion-wall, so selecting it offered no clickable wall lines and the card was simply uncastable. The LOS dimming that appears alongside is correct and stays: placement requires sight of the wall line, so the lit squares show where the shimmering can go. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>