.

src/test/java/kz/konturai/parser/service/MarketingAnalysisServiceChartPlacementTest.java

@@ -10,6 +10,7 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
+import java.util.regex.Pattern;
 
 import org.junit.jupiter.api.Test;
 
@@ -153,4 +154,21 @@ class MarketingAnalysisServiceChartPlacementTest {
         assertTrue(section7Body.contains("[[CHART_CHANNEL_MATRIX]]"),
                 "Must insert CHART_CHANNEL_MATRIX into section VII");
     }
+
+    @Test
+    void buildChartJsonBlock_shouldStartWithJsonKey_andEndWithDoubleNewline() throws Exception {
+        Method m = MarketingAnalysisService.class.getDeclaredMethod("buildChartJsonBlock", String.class, String.class);
+        m.setAccessible(true);
+
+        String out = (String) m.invoke(marketingAnalysisService, "segmentsChannelMatrix", "{\"a\":1}");
+
+        assertTrue(out.startsWith("```json:segmentsChannelMatrix\n"),
+                "Block must start strictly with ```json:<key> and newline");
+        assertTrue(out.endsWith("\n```\n\n"), "Block must end with closing fence followed by two newlines");
+
+        // Ensure there is no whitespace before opening fence (strict parsing on
+        // frontend)
+        assertTrue(Pattern.compile("(?m)^```json:segmentsChannelMatrix$").matcher(out).find(),
+                "Opening fence line must be exactly ```json:<key> with no leading spaces");
+    }
 }