feat: add public product catalog boundary

apps/api/tests/application/public-product-service.test.js

@@ -0,0 +1,42 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { createPublicProductService } from '../../src/modules/products/services/public-product-service.js';
+
+test('returns only a publicly visible product', async () => {
+  const service = createPublicProductService({
+    productRepository: {
+      async findPublicBySlug(slug) {
+        assert.equal(slug, 'pikachu-plush');
+        return {
+          id: 'product-1',
+          sellerId: 'private-seller-id',
+          categoryId: 'category-1',
+          name: 'Pikachu Plush',
+          slug,
+          description: 'A friendly plush.',
+        };
+      },
+    },
+  });
+
+  assert.deepEqual(await service.getBySlug('pikachu-plush'), {
+    id: 'product-1',
+    sellerId: 'private-seller-id',
+    categoryId: 'category-1',
+    name: 'Pikachu Plush',
+    slug: 'pikachu-plush',
+    description: 'A friendly plush.',
+  });
+});
+
+test('returns a not-found application error for non-public products', async () => {
+  const service = createPublicProductService({
+    productRepository: { async findPublicBySlug() { return null; } },
+  });
+
+  await assert.rejects(
+    () => service.getBySlug('hidden-product'),
+    (error) => error.code === 'PRODUCT_NOT_FOUND' && error.statusCode === 404,
+  );
+});