fix(vscode,ui): stop postMessage crash when opening chat in Cursor (#2335)

VS Code webviews delete window.parent, so ChatContainer's settings-sync
effect threw TypeError on chat open. Also harden the webview bridge when
acquireVsCodeApi() returns undefined and SSE panel disposal races.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/components/chat/ChatContainer.tsx

@@ -715,10 +715,15 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
     const promptReadOnly = parentSession ? !allowPromptingSubagentSessions : readOnly;
 
     React.useEffect(() => {
-        if (typeof window === 'undefined' || window.parent === window) {
+        // VS Code/Cursor/Positron webviews delete window.parent (and window.top).
+        // The old `window.parent === window` check does not catch that, so
+        // `window.parent.postMessage(...)` threw on chat open:
+        // TypeError: Cannot read properties of undefined (reading 'postMessage')
+        if (typeof window === 'undefined' || !window.parent || window.parent === window) {
             return;
         }
 
+        const parentWindow = window.parent;
         const applySetting = (value: boolean) => {
             useUIStore.getState().setAllowPromptingSubagentSessions(value);
         };
@@ -729,7 +734,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
             applySetting(payload.allowPromptingSubagentSessions);
         };
         const handleMessage = (event: MessageEvent) => {
-            if (event.source !== window.parent || event.origin !== window.location.origin) return;
+            if (event.source !== parentWindow || event.origin !== window.location.origin) return;
             const data = event.data as { type?: unknown; payload?: { allowPromptingSubagentSessions?: unknown } };
             if (data?.type !== 'openchamber:chat-settings-sync'
                 || typeof data.payload?.allowPromptingSubagentSessions !== 'boolean') return;
@@ -738,7 +743,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
 
         scopedWindow.__openchamberApplyChatSettingsSync = applySync;
         window.addEventListener('message', handleMessage);
-        window.parent.postMessage({ type: 'openchamber:chat-settings-request' }, window.location.origin);
+        parentWindow.postMessage({ type: 'openchamber:chat-settings-request' }, window.location.origin);
         return () => {
             window.removeEventListener('message', handleMessage);
             if (scopedWindow.__openchamberApplyChatSettingsSync === applySync) {

packages/ui/src/components/chat/__tests__/parentFramePostMessageGuard.test.ts

@@ -0,0 +1,42 @@
+import { describe, expect, test } from 'bun:test';
+
+/**
+ * Mirrors the ChatContainer chat-settings-sync guard.
+ * VS Code/Cursor/Positron webviews delete `window.parent`, so the old
+ * `window.parent === window` check still fell through to `.postMessage` and
+ * crashed chat open with:
+ * TypeError: Cannot read properties of undefined (reading 'postMessage')
+ */
+const canPostMessageToParentFrame = (win: { parent?: unknown } | undefined): boolean => {
+  if (typeof win === 'undefined' || !win) return false;
+  return Boolean(win.parent) && win.parent !== win;
+};
+
+describe('parent-frame postMessage guard (VS Code webview)', () => {
+  test('rejects when parent was deleted (VS Code webview injector behavior)', () => {
+    const vscodeLikeWindow = { parent: undefined };
+    expect(canPostMessageToParentFrame(vscodeLikeWindow)).toBe(false);
+  });
+
+  test('rejects when parent is null', () => {
+    expect(canPostMessageToParentFrame({ parent: null })).toBe(false);
+  });
+
+  test('rejects top-level windows where parent === self', () => {
+    const topLevel = {} as { parent?: unknown };
+    topLevel.parent = topLevel;
+    expect(canPostMessageToParentFrame(topLevel)).toBe(false);
+  });
+
+  test('allows real embedded iframe parent windows', () => {
+    const parent = {};
+    const child = { parent };
+    expect(canPostMessageToParentFrame(child)).toBe(true);
+  });
+
+  test('old guard incorrectly allows deleted parent', () => {
+    const vscodeLikeWindow = { parent: undefined as unknown };
+    const oldGuardWouldSkip = vscodeLikeWindow.parent === vscodeLikeWindow;
+    expect(oldGuardWouldSkip).toBe(false);
+  });
+});