*
     * @param sessionId the session ID (can be null to create a new session)
     * @param userId the user ID
     * @return the existing or new session
     */
    public ChatSession getOrCreateSession(final String sessionId, final String userId) {
        if (sessionId != null) {
            final ChatSession session = findSession(sessionId);
            if (session != null) {

            logger.debug("[RAG] Starting chat request. sessionId={}, userId={}, userMessage={}", sessionId, userId, userMessage);
        }

        final ChatSession session = chatSessionManager.getOrCreateSession(sessionId, userId);
        // Extract history snapshot before adding current user message to avoid duplication
        final List<LlmMessage> history = extractHistory(session);