feat(M01-A): 建立后端API基础骨架

backend/src/app.ts

@@ -0,0 +1,54 @@
+import { randomUUID } from 'node:crypto';
+import cors from '@fastify/cors';
+import rateLimit from '@fastify/rate-limit';
+import Fastify, { type FastifyInstance } from 'fastify';
+import { loadConfig, type AppConfig } from './config.js';
+import { registerHealthRoutes } from './routes/health.js';
+
+export interface BuildAppOptions {
+  config?: AppConfig;
+}
+
+declare module 'fastify' {
+  interface FastifyRequest {
+    traceId: string;
+  }
+}
+
+export async function buildApp(options: BuildAppOptions = {}): Promise<FastifyInstance> {
+  const config = options.config ?? loadConfig();
+  const app = Fastify({
+    logger: {
+      level: config.nodeEnv === 'test' ? 'silent' : 'info'
+    },
+    genReqId: () => randomUUID()
+  });
+
+  app.decorateRequest('traceId', '');
+  app.addHook('onRequest', async (request, reply) => {
+    const traceHeader = request.headers['x-trace-id'];
+    request.traceId = Array.isArray(traceHeader) ? traceHeader[0] : traceHeader || request.id;
+    reply.header('x-trace-id', request.traceId);
+  });
+
+  await app.register(cors, {
+    origin: config.corsOrigins
+  });
+  await app.register(rateLimit, {
+    max: 120,
+    timeWindow: '1 minute'
+  });
+
+  app.setErrorHandler((error, request, reply) => {
+    request.log.error({ err: error, traceId: request.traceId }, 'request failed');
+    reply.status(500).send({
+      code: 'INTERNAL_ERROR',
+      message: 'Internal server error',
+      traceId: request.traceId
+    });
+  });
+
+  await registerHealthRoutes(app, config);
+
+  return app;
+}