Fix duplicate marketplace categories from case-sensitive displayName matching

rewrite-core/src/main/java/org/openrewrite/marketplace/RecipeMarketplace.java

@@ -79,7 +79,7 @@ public void merge(Category category) {
             for (Category subCategory : category.categories) {
                 Category existingSubCategory = null;
                 for (Category c : categories) {
-                    if (c.getDisplayName().equals(subCategory.getDisplayName())) {
+                    if (c.getDisplayName().equalsIgnoreCase(subCategory.getDisplayName())) {
                         existingSubCategory = c;
                         break;
                     }
@@ -154,7 +154,7 @@ public void install(RecipeListing recipe, List<CategoryDescriptor> categoryPath)
 
         private Category findOrCreateCategory(CategoryDescriptor categoryDescriptor) {
             for (Category category : categories) {
-                if (category.getDisplayName().equals(categoryDescriptor.getDisplayName())) {
+                if (category.getDisplayName().equalsIgnoreCase(categoryDescriptor.getDisplayName())) {
                     return category;
                 }
             }

rewrite-core/src/test/java/org/openrewrite/marketplace/RecipeMarketplaceReaderTest.java

@@ -436,6 +436,50 @@ void mergePreservesMetadata() {
         assertThat(mergedOther.getMetadata().get("embedding")).isEqualTo("xyz789");
     }
 
+    @Test
+    void mergeCategoriesCaseInsensitive() {
+        // Simulates the real-world scenario where rewrite-java defines category "AI"
+        // and rewrite-ai defines category "ai" -- these should merge into one category
+        RecipeMarketplace marketplace1 = new RecipeMarketplaceReader().fromCsv("""
+          name,category1,ecosystem,packageName
+          org.openrewrite.java.ai.ClassDefinitionLength,AI,maven,org.openrewrite:rewrite-java
+          org.openrewrite.java.ai.MethodDefinitionLength,AI,maven,org.openrewrite:rewrite-java
+          """);
+
+        RecipeMarketplace marketplace2 = new RecipeMarketplaceReader().fromCsv("""
+          name,category1,ecosystem,packageName
+          io.moderne.ai.FindAgentsInUse,ai,maven,io.moderne.recipe:rewrite-ai
+          io.moderne.ai.FindLibrariesInUse,ai,maven,io.moderne.recipe:rewrite-ai
+          """);
+
+        marketplace1.getRoot().merge(marketplace2.getRoot());
+
+        assertThat(marketplace1.getRoot().getCategories())
+          .as("AI and ai should merge into a single category")
+          .hasSize(1);
+        assertThat(marketplace1.getRoot().getCategories().getFirst().getRecipes()).hasSize(4);
+        // The first-seen casing wins
+        assertThat(marketplace1.getRoot().getCategories().getFirst().getDisplayName()).isEqualTo("AI");
+    }
+
+    @Test
+    void installCategoriesCaseInsensitive() {
+        // When installing recipes via CSV where one uses "AI" and another uses "ai"
+        // in the same category position, they should land in the same category
+        RecipeMarketplace marketplace = new RecipeMarketplaceReader().fromCsv("""
+          name,category1,ecosystem,packageName
+          org.example.Recipe1,AI,maven,org.example:test1
+          org.example.Recipe2,ai,maven,org.example:test2
+          """);
+
+        assertThat(marketplace.getRoot().getCategories())
+          .as("AI and ai should be treated as the same category during install")
+          .hasSize(1);
+        assertThat(marketplace.getRoot().getCategories().getFirst().getRecipes()).hasSize(2);
+        // The first-seen casing wins
+        assertThat(marketplace.getRoot().getCategories().getFirst().getDisplayName()).isEqualTo("AI");
+    }
+
     private static RecipeMarketplace.Category findCategory(RecipeMarketplace.Category category, String name) {
         return category.getCategories().stream()
           .filter(c -> c.getDisplayName().equals(name))