Implement enum rename detection in MarkdownRender

- Enhanced listDiff method to detect 1:1 enum renames (1 added + 1 removed = rename)
- Shows "Renamed enum value: OldValue -> NewValue" instead of separate Added/Removed
- Falls back to original behavior for other cases (multiple changes, only additions, etc.)
- Added comprehensive test cases to verify all scenarios

Co-authored-by: DrSatyr <[email protected]>

Author: Copilot

core/src/main/java/org/openapitools/openapidiff/core/output/MarkdownRender.java

@@ -432,6 +432,18 @@ protected String listDiff(int deepness, String name, ChangedList<?> listDiff) {
     if (listDiff == null) {
       return "";
     }
+
+    // Check if this looks like a simple rename (1 added, 1 removed)
+    if (listDiff.getIncreased().size() == 1 && listDiff.getMissing().size() == 1) {
+      StringBuilder sb = new StringBuilder();
+      Object oldValue = listDiff.getMissing().get(0);
+      Object newValue = listDiff.getIncreased().get(0);
+      sb.append(format("%sRenamed %s value:\n\n", indent(deepness), name));
+      sb.append(format("%s* `%s` -> `%s`\n", indent(deepness), oldValue, newValue));
+      return sb.toString();
+    }
+
+    // Fall back to current behavior for other cases
     return listItem(deepness, "Added " + name, listDiff.getIncreased())
         + listItem(deepness, "Removed " + name, listDiff.getMissing());
   }

core/src/test/java/org/openapitools/openapidiff/core/output/MarkdownRenderTest.java

@@ -4,8 +4,11 @@
 
 import java.io.ByteArrayOutputStream;
 import java.io.OutputStreamWriter;
+import java.util.Arrays;
+import java.util.Collections;
 import org.junit.jupiter.api.Test;
 import org.openapitools.openapidiff.core.OpenApiCompare;
+import org.openapitools.openapidiff.core.model.ChangedList;
 import org.openapitools.openapidiff.core.model.ChangedOpenApi;
 
 public class MarkdownRenderTest {
@@ -40,4 +43,45 @@ public void renderDoesNotFailWhenHTTPStatusCodeIsRange() {
     render.render(diff, outputStreamWriter);
     assertThat(outputStream.toString()).isNotBlank();
   }
+
+  @Test
+  public void testEnumRenameDetection() {
+    MarkdownRender render = new MarkdownRender();
+
+    // Test 1:1 rename (should show as rename)
+    ChangedList<String> enumRename =
+        org.openapitools.openapidiff.core.compare.ListDiff.diff(
+            new ChangedList.SimpleChangedList<>(
+                Collections.singletonList("OldValue"), Collections.singletonList("NewValue")));
+    String renameResult = render.listDiff(2, "enum", enumRename);
+    assertThat(renameResult).contains("Renamed enum value:");
+    assertThat(renameResult).contains("`OldValue` -> `NewValue`");
+
+    // Test multiple additions and removals (should fall back to original behavior)
+    ChangedList<String> enumMultiple =
+        org.openapitools.openapidiff.core.compare.ListDiff.diff(
+            new ChangedList.SimpleChangedList<>(
+                Arrays.asList("OldValue1", "OldValue2"), Arrays.asList("NewValue1", "NewValue2")));
+    String multipleResult = render.listDiff(2, "enum", enumMultiple);
+    assertThat(multipleResult).contains("Added enum values:");
+    assertThat(multipleResult).contains("Removed enum values:");
+
+    // Test single addition (should use original behavior)
+    ChangedList<String> enumAdd =
+        org.openapitools.openapidiff.core.compare.ListDiff.diff(
+            new ChangedList.SimpleChangedList<>(
+                Collections.emptyList(), Collections.singletonList("NewValue")));
+    String addResult = render.listDiff(2, "enum", enumAdd);
+    assertThat(addResult).contains("Added enum value:");
+    assertThat(addResult).doesNotContain("Renamed");
+
+    // Test single removal (should use original behavior)
+    ChangedList<String> enumRemove =
+        org.openapitools.openapidiff.core.compare.ListDiff.diff(
+            new ChangedList.SimpleChangedList<>(
+                Collections.singletonList("OldValue"), Collections.emptyList()));
+    String removeResult = render.listDiff(2, "enum", enumRemove);
+    assertThat(removeResult).contains("Removed enum value:");
+    assertThat(removeResult).doesNotContain("Renamed");
+  }
 }