Import source: app/backend/src/plugins/request-id

Import the existing local project snapshot. This commit organizes existing files; it does not represent newly developed functionality.

app/backend/src/plugins/request-id.ts

@@ -0,0 +1,24 @@
+import fp from 'fastify-plugin';
+import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
+import { randomBytes } from 'node:crypto';
+
+const HEADER = 'x-request-id';
+
+declare module 'fastify' {
+  interface FastifyRequest {
+    requestId: string;
+  }
+}
+
+export default fp(async function requestIdPlugin(app: FastifyInstance) {
+  app.addHook('onRequest', async (req: FastifyRequest, _reply: FastifyReply) => {
+    const incoming = req.headers[HEADER];
+    req.requestId = typeof incoming === 'string' && incoming.length > 0
+      ? incoming.slice(0, 64)
+      : randomBytes(12).toString('hex');
+  });
+
+  app.addHook('onSend', async (_req: FastifyRequest, reply: FastifyReply) => {
+    reply.header(HEADER, _req.requestId);
+  });
+});