# fix(react): resolve React 19 / Storybook structuredClone crashes

packages/react/.storybook/preview.js

@@ -1,9 +1,48 @@
 import 'normalize.css';
 
+// ─── React 19 logComponentRender patch ───────────────────────────────────────
+// React 19's dev-mode calls performance.measure() with a `detail` option that
+// contains component prop diffs. The browser internally structured-clones that
+// detail, and crashes with:
+//   "DOMException: unsupported type for structured data"
+// when the EmbeddedChatApi context value (which holds WebSocket/Promises) is
+// diffed as a prop on the Context.Provider component.
+//
+// We can't configure this away — it's baked into react-dom-client.development.js.
+// The patch below wraps performance.measure so the DOMException is caught and
+// the call is retried without the non-serializable detail, keeping the browser's
+// performance timeline intact for everything else.
+if (typeof performance !== 'undefined' && typeof performance.measure === 'function') {
+  const _originalMeasure = performance.measure.bind(performance);
+  performance.measure = function patchedMeasure(name, startOrOptions, endMark) {
+    try {
+      if (typeof startOrOptions === 'object' && startOrOptions !== null) {
+        return _originalMeasure(name, startOrOptions, endMark);
+      }
+      return _originalMeasure(name, startOrOptions, endMark);
+    } catch (e) {
+      if (e instanceof DOMException) {
+        // Retry without the detail so the mark still appears in DevTools
+        try {
+          const safe = { ...startOrOptions };
+          delete safe.detail;
+          return _originalMeasure(name, safe);
+        } catch (_) { /* ignore */ }
+      } else {
+        throw e;
+      }
+    }
+  };
+}
+
 /** @type { import('@storybook/react').Preview } */
 const preview = {
   parameters: {
-    actions: { argTypesRegex: '^on[A-Z].*' },
+    // IMPORTANT: Do NOT re-enable argTypesRegex here.
+    // Storybook's action addon auto-wraps any on* prop matching the regex and
+    // tries to structured-clone every argument via postMessage. File/Blob objects
+    // are not cloneable and would cause the same DOMException.
+    actions: { disable: true },
     controls: {
       matchers: {
         color: /(background|color)$/i,
@@ -14,3 +53,4 @@ const preview = {
 };
 
 export default preview;
+