[chat]Fix chatbot open state flaky (#10900)

* Fix chatbot open state flaky

Signed-off-by: Lin Wang <[email protected]>

* Changeset file for PR #10900 created/updated

---------

Signed-off-by: Lin Wang <[email protected]>
Co-authored-by: opensearch-changeset-bot[bot] <154024398+opensearch-changeset-bot[bot]@users.noreply.github.com>

Author: wanglam

changelogs/fragments/10900.yml

@@ -0,0 +1,2 @@
+fix:
+- Fix chatbot open state flaky ([#10900](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/10900))

src/plugins/chat/public/components/chat_header_button.tsx

@@ -169,9 +169,17 @@ export const ChatHeaderButton = React.forwardRef<ChatHeaderButtonInstance, ChatH
     });
 
     useEffectOnce(() => {
-      if (isOpen) {
-        openSidecar();
+      if (!isOpen) {
+        return;
       }
+
+      const rafId = window.requestAnimationFrame(() => {
+        openSidecar();
+      });
+
+      return () => {
+        window.cancelAnimationFrame(rafId);
+      };
     });
 
     return (