fix(kernel-browser-runtime): fix test mock recursion and iframe creation error handling

- Save original document.createElement before mocking to prevent infinite
  recursion when creating non-iframe elements in tests
- Move iframe creation inside try block so ID is removed from
  launchesInProgress if createIframe throws

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: sirtimid

packages/kernel-browser-runtime/src/ui/UIOrchestrator.test.ts

@@ -145,6 +145,9 @@ const makeIframe = (): HTMLIFrameElement & {
   };
 };
 
+// Save original createElement before any mocking
+const originalCreateElement = document.createElement.bind(document);
+
 describe('UIOrchestrator', () => {
   let mainSlot: ReturnType<typeof makeContainer>;
   let orchestrator: UIOrchestrator;
@@ -163,7 +166,7 @@ describe('UIOrchestrator', () => {
           createdIframes.push(iframe);
           return iframe as unknown as HTMLElement;
         }
-        return document.createElement(tagName);
+        return originalCreateElement(tagName);
       },
     );
 

packages/kernel-browser-runtime/src/ui/UIOrchestrator.ts

@@ -143,16 +143,17 @@ export class UIOrchestrator {
 
     this.#logger.info(`Launching UI vat: ${id} in slot: ${slot}`);
 
-    const iframe = this.#createIframe(id, uri, title, visible);
-    slotElement.appendChild(iframe);
-
+    let iframe: HTMLIFrameElement | undefined;
     let port: MessagePort;
     try {
+      iframe = this.#createIframe(id, uri, title, visible);
+      slotElement.appendChild(iframe);
+
       // Wait for iframe to load and establish MessageChannel
       port = await this.#establishConnection(iframe);
     } catch (error) {
-      // Clean up iframe if connection establishment fails
-      iframe.remove();
+      // Clean up iframe if it was created and appended
+      iframe?.remove();
       this.#launchesInProgress.delete(id);
       throw error;
     }