[eric] canvas: NOTHING drags in fullscreen (untileForDrag chokepoint + guards on app and window cards; exit is the pill, green dot, or Escape)

frontend/src/app/pages/Dashboard/cards/CanvasWindowCard.tsx

@@ -85,6 +85,8 @@ const CanvasWindowCard: React.FC<CanvasWindowCardProps> = ({
 
   const onHeaderPointerDown = useCallback((e: React.PointerEvent) => {
     if (e.button !== 0) return;
+    // Fullscreen has no drag (macOS rule); same guard as AgentCard/BrowserCard.
+    if (tiling.zone === 'fullscreen') return;
     const target = e.target as HTMLElement;
     if (target.closest('[data-no-drag], button, [role="button"], input, textarea, select')) return;
     e.preventDefault();

frontend/src/app/pages/Dashboard/cards/DashboardViewCard.tsx

@@ -396,6 +396,8 @@ const DashboardViewCard: React.FC<Props> = ({
 
   const handleDragPointerDown = useCallback((e: React.PointerEvent) => {
     if (e.button !== 0) return;
+    // Fullscreen has no drag (macOS rule); same guard as AgentCard/BrowserCard.
+    if (tiling.zone === 'fullscreen') return;
     e.preventDefault();
     e.stopPropagation();
     const cs = getCanvasState();

frontend/src/app/pages/Dashboard/cards/useCardTiling.ts

@@ -70,6 +70,8 @@ export function useCardTiling({ cardId, getCanvasState, commitPosition }: CardTi
   }, [tiledFrame, dispatch, cardId]);
 
   const untileForDrag = useCallback((clientX: number, clientY: number, preTileWidth: number): { x: number; y: number } | null => {
+    // Fullscreen never drag-untiles (macOS rule; also every card's own drag guard): exiting is the pill/green dot/Escape, never a stray header wiggle.
+    if (zone === 'fullscreen') return null;
     const frame = tiledFrame();
     if (!frame) return null;
     const cam = getCanvasState();