final double headRatio = (double) head.length() / (head.length() + tail.length());
        assertTrue(headRatio > 0.55 && headRatio < 0.65);
    }

    @Test
    public void test_smartSummary_withMultipleSources() {
        final ChatMessage msg = createAssistantWithSources("A".repeat(1000), "Guide A", "Guide B", "Guide C");