Keep an inline panel drawing when its host reports it hidden

Claude reports a panel on screen as hidden, which stopped the app's
render loop and the browser's animation frames, so no map was drawn. An
inline panel no longer suspends rendering when hidden, and draws from a
timer while animation frames stop arriving.

src/app/embed.js

@@ -45,6 +45,39 @@ export function isEmbeddedInline() {
   return globalThis.GEV_EMBED_INLINE === true;
 }
 
+// A panel keeps drawing at about this rate when its host stops animation
+// frames; see keepPanelRendering.
+const PANEL_FRAME_MS = 33;
+const MISSED_FRAMES_MS = 250;
+
+/**
+ * Keep the globe drawing in an inline panel. Some hosts report a panel on
+ * screen as hidden, which stops the browser's animation frames and with them
+ * Cesium's render loop; while frames stop arriving, draw from a timer.
+ * Returns a function that stops it.
+ */
+export function keepPanelRendering(
+  viewer,
+  { windowRef = globalThis.window, now = () => performance.now() } = {},
+) {
+  let lastFrame = now();
+  let frameRequest = null;
+  const onFrame = () => {
+    lastFrame = now();
+    frameRequest = windowRef.requestAnimationFrame(onFrame);
+  };
+  frameRequest = windowRef.requestAnimationFrame(onFrame);
+  const timer = windowRef.setInterval(() => {
+    if (now() - lastFrame < MISSED_FRAMES_MS || viewer.isDestroyed?.()) return;
+    viewer.resize();
+    viewer.render();
+  }, PANEL_FRAME_MS);
+  return () => {
+    windowRef.clearInterval(timer);
+    windowRef.cancelAnimationFrame(frameRequest);
+  };
+}
+
 const delay = (ms, signal) =>
   new Promise((resolve) => {
     const timer = setTimeout(resolve, ms);
@@ -169,6 +202,9 @@ export function installViews({
 
   windowRef.document.body.classList.add('ui-embed');
   shell.setCleanView?.(true);
+  const stopRendering = isEmbeddedInline()
+    ? keepPanelRendering(viewer, { windowRef })
+    : () => {};
   // A framing page talks to the app across frames; an inline panel shares
   // the page with it and talks through the page's own window.
   const peer = isEmbeddedInline() ? windowRef : windowRef.parent;
@@ -209,5 +245,8 @@ export function installViews({
   void ready.then(() => {
     if (!signal?.aborted) post({ type: EMBED_READY_MESSAGE });
   });
-  return () => windowRef.removeEventListener('message', onMessage);
+  return () => {
+    stopRendering();
+    windowRef.removeEventListener('message', onMessage);
+  };
 }