this.lastAccessedAt = LocalDateTime.now();
    }

    /**
     * Returns the number of messages in this session.
     *
     * @return the message count
     */
    public int getMessageCount() {
        synchronized (messagesLock) {
            return messages != null ? messages.size() : 0;
        }
    }

    /**

        final ChatSession session = new ChatSession();
        assertEquals(0, session.getMessageCount());

        session.addUserMessage("First");
        assertEquals(1, session.getMessageCount());

        session.addAssistantMessage("Second");
        assertEquals(2, session.getMessageCount());
    }

    @Test
    public void test_getMessageCountWithNullMessages() {