Add catalog model layers with JSON Schema based kind declarations

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Fredrik Adelöw <freben@spotify.com>

plugins/scaffolder-common/report-alpha.api.md

@@ -4,6 +4,7 @@
 
 ```ts
 import { BasicPermission } from '@backstage/plugin-permission-common';
+import { CatalogModelLayer } from '@backstage/catalog-model/alpha';
 import { ResourcePermission } from '@backstage/plugin-permission-common';
 
 // @alpha
@@ -50,6 +51,9 @@ export const taskReadPermission: ResourcePermission<'scaffolder-task'>;
 // @alpha
 export const templateManagementPermission: BasicPermission;
 
+// @alpha
+export const templateModelLayer: CatalogModelLayer;
+
 // @alpha
 export const templateParameterReadPermission: ResourcePermission<'scaffolder-template'>;
 

plugins/scaffolder-common/src/alpha.ts

@@ -15,3 +15,4 @@
  */
 
 export * from './permissions';
+export { templateModelLayer } from './catalogModel';

plugins/scaffolder-common/src/catalogModel.ts

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2026 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { createCatalogModelLayer } from '@backstage/catalog-model/alpha';
+import schema from './Template.v1beta3.schema.json';
+
+/**
+ * Extends the catalog model with the Template kind.
+ *
+ * @alpha
+ */
+export const templateModelLayer = createCatalogModelLayer({
+  layerId: 'Template',
+  builder: model => {
+    model.addKind({
+      group: 'scaffolder.backstage.io',
+      names: {
+        kind: 'Template',
+        singular: 'template',
+        plural: 'templates',
+      },
+      description: 'A template for scaffolding a new component',
+      versions: [
+        {
+          name: 'v1beta3',
+          relationFields: [
+            {
+              selector: { path: 'spec.owner' },
+              relation: 'ownedBy',
+              defaultKind: 'Group',
+              // TODO: This was inherit since before, but should ownership in general be default instead?
+              defaultNamespace: 'inherit',
+              allowedKinds: ['Group', 'User'],
+            },
+          ],
+          schema: {
+            jsonSchema: schema as any,
+          },
+        },
+      ],
+    });
+  },
+});