Keep the panel's 2D canvases in memory

In Claude, the app's 2D overlay canvases covered the globe in black
while the host treated the panel as off screen, and the globe showed
once they were hidden. The panel now asks for 2D canvases backed by
memory rather than the GPU.

src/app/globePanelRuntime.js

@@ -341,6 +341,16 @@ export function panelRuntime(config) {
     };
     window.Worker.prototype = NativeWorker.prototype;
 
+    // Some hosts drop the GPU contents of a panel's 2D canvases while they
+    // consider the panel off screen, and the overlays then cover the globe
+    // in black. Keep 2D canvases in memory instead, which hosts do not drop.
+    const getContext = HTMLCanvasElement.prototype.getContext;
+    HTMLCanvasElement.prototype.getContext = function (type, options) {
+      return type === '2d'
+        ? getContext.call(this, type, { ...options, willReadFrequently: true })
+        : getContext.call(this, type, options);
+    };
+
     // Markup the app adds as HTML text would request its images from this
     // page's site at once; hold their addresses until the files are here.
     const htmlWithHeldImages = (html) =>