Avoid hub iframe overlay on embed shell tab switches.

Use in-shell content loading state instead of parent postMessage so tab changes do not trigger the full instance-frame loading mask.

Co-authored-by: Cursor <cursoragent@cursor.com>

static/instance_embed.js

@@ -33,16 +33,9 @@
     return "";
   }
 
-  function notifyParentNavStart() {
-    try {
-      window.parent.postMessage({ type: "instance-frame-navigating" }, "*");
-    } catch (_) {}
-  }
-
-  function notifyParentReady() {
-    try {
-      window.parent.postMessage({ type: "instance-frame-ready" }, "*");
-    } catch (_) {}
+  function setRootLoading(on) {
+    const root = document.getElementById("embed-page-root");
+    if (root) root.classList.toggle("is-embed-tab-loading", !!on);
   }
 
   function setNavActive(tab) {
@@ -99,7 +92,7 @@
     if (!tab || loadingTab) return;
     const token = ++navToken;
     loadingTab = true;
-    notifyParentNavStart();
+    setRootLoading(true);
     try {
       const qs = listWindowQueryString();
       const url = "/api/embed/page/" + encodeURIComponent(tab) + (qs ? "?" + qs : "");
@@ -122,7 +115,7 @@
     } finally {
       if (token === navToken) {
         loadingTab = false;
-        notifyParentReady();
+        setRootLoading(false);
       }
     }
   }
@@ -214,7 +207,9 @@
     patchHardNavigations();
     bindNav();
     runPageInit(getTab());
-    notifyParentReady();
+    try {
+      window.parent.postMessage({ type: "instance-frame-ready" }, "*");
+    } catch (_) {}
   }
 
   global.InstanceEmbed = {