diff --git a/App.tsx b/App.tsx
index cecce47..c17ecbc 100644
--- a/App.tsx
+++ b/App.tsx
@@ -4,6 +4,7 @@
  * Main application component with authentication routing.
  * Shows loading screen while restoring auth state.
  */
+import './src/polyfills';
 
 import React from 'react';
 import { Buffer } from 'buffer';
diff --git a/assets/images/icon.png b/assets/images/icon.png
new file mode 100644
index 0000000..f37764b
Binary files /dev/null and b/assets/images/icon.png differ
diff --git a/src/polyfills.ts b/src/polyfills.ts
new file mode 100644
index 0000000..c9c8fde
--- /dev/null
+++ b/src/polyfills.ts
@@ -0,0 +1,15 @@
+/**
+ * Polyfills that must run before any other app code (including LangChain/LangGraph).
+ * This file is imported as the very first line in App.tsx so that ReadableStream
+ * exists before @langchain/core or @langchain/langgraph are loaded.
+ */
+import 'web-streams-polyfill';
+
+// Ensure globalThis has ReadableStream (main polyfill may not patch in RN/Metro)
+const g = typeof globalThis !== 'undefined' ? globalThis : (typeof global !== 'undefined' ? global : (typeof self !== 'undefined' ? self : {}));
+if (typeof (g as any).ReadableStream === 'undefined') {
+  const ponyfill = require('web-streams-polyfill/dist/ponyfill.js');
+  (g as any).ReadableStream = ponyfill.ReadableStream;
+  (g as any).WritableStream = ponyfill.WritableStream;
+  (g as any).TransformStream = ponyfill.TransformStream;
+}