assertEquals("Message 5", session.getMessages().get(0).getContent());
        assertEquals("Message 9", session.getMessages().get(4).getContent());
    }

    @Test
    public void test_trimHistoryStartsWithUserMessage() {
        final ChatSession session = new ChatSession();
        // Create: user, assistant, user, assistant, user, assistant (6 messages)
        session.addUserMessage("User 1");