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/vscode/webview/api/bridge.ts

@@ -9,10 +9,24 @@ interface VSCodeAPI {
 }
 
 let vscodeApi: VSCodeAPI | null = null;
+let noopWarned = false;
+
+const noopVSCodeApi: VSCodeAPI = {
+  postMessage: (message) => {
+    // acquireVsCodeApi() can return undefined in broken/non-standard webview slots
+    // (Cursor after extension update, VSCodium, headless). Drop the message instead
+    // of throwing TypeError: Cannot read properties of undefined (reading 'postMessage').
+    if (!noopWarned) {
+      noopWarned = true;
+      console.warn('[openchamber] VS Code API unavailable; dropping postMessage', message);
+    }
+  },
+};
 
 function getVSCodeAPI(): VSCodeAPI {
   if (!vscodeApi) {
-    vscodeApi = acquireVsCodeApi();
+    const acquired = typeof acquireVsCodeApi === 'function' ? acquireVsCodeApi() : undefined;
+    vscodeApi = acquired ?? noopVSCodeApi;
   }
   return vscodeApi;
 }