chore: add gateway scaffold

src/plugins/graphql.ts

@@ -0,0 +1,32 @@
+import { FastifyInstance } from 'fastify';
+import fp from 'fastify-plugin';
+import mercurius from 'mercurius';
+
+const typeDefs = /* GraphQL */ `
+  type Query {
+    _ping: String
+  }
+
+  # TODO(gateway-next): Extend schema with federation v2 directives and compose remote schemas.
+`;
+
+const resolvers = {
+  Query: {
+    _ping: async () => 'pong',
+  },
+};
+
+async function graphqlPlugin(fastify: FastifyInstance) {
+  fastify.register(mercurius, {
+    schema: typeDefs,
+    resolvers,
+    graphiql: process.env.NODE_ENV !== 'production',
+    context: () => ({
+      // TODO(gateway-next): Inject authenticated user + stitched service clients.
+    }),
+  });
+}
+
+export default fp(graphqlPlugin, {
+  name: 'graphql-plugin',
+});