>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3488961. --> Reported by: [ayrmax](https://www.drupal.org/user/1625944) >>> <h3 id="summary-problem-motivation">Problem/Motivation</h3> <p>When using streamed output with the "Allow History" option enabled in the Assistant, and the user is anonymous, an error occurs in the streamed message output. The error details are as follows:</p> <pre>Failed to start the session because headers have already been sent by "/var/www/html/web/modules/contrib/ai/modules/ai_chatbot/src/Form/ChatForm.php" at line 159. in Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage-&gt;start() (line 132 of /var/www/html/vendor/symfony/http-foundation/Session/Storage/NativeSessionStorage.php).</pre><h4 id="summary-steps-reproduce">Steps to reproduce</h4> <ol> <li>Create an Assistant with the "Allow History" setting enabled and set to any "Session"-based option.</li> <li>Add the Assistant to a Chatbox block and enable streaming for the output.</li> <li>Interact with the Assistant through the Chatbox block as an anonymous user.</li> <li>Observe the error message appearing beneath the Assistant's response.</li> </ol> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <p>The issue occurs because the ChatForm starts sending data before a session is initialized. To resolve this, I ensured that the session is initialized before any output is sent if it hasn't already been started.</p> <p>I provided a patch to fix the issue.</p>