fix: wrap authPlugin with fastify-plugin to expose decorator to child contexts

The authenticate decorator was encapsulated and invisible to route handlers
registered in child scopes, causing "request.server.authenticate is not a function".
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package-lock.json

@@ -17,6 +17,7 @@
         "@supabase/supabase-js": "^2.49.1",
         "drizzle-orm": "^0.38.3",
         "fastify": "^5.1.0",
+        "fastify-plugin": "^5.1.0",
         "jsonwebtoken": "^9.0.2",
         "nanoid": "^5.0.9",
         "postgres": "^3.4.5",

package.json

@@ -27,6 +27,7 @@
     "@supabase/supabase-js": "^2.49.1",
     "drizzle-orm": "^0.38.3",
     "fastify": "^5.1.0",
+    "fastify-plugin": "^5.1.0",
     "jsonwebtoken": "^9.0.2",
     "nanoid": "^5.0.9",
     "postgres": "^3.4.5",

src/plugins/auth.plugin.ts

 import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
+import fp from 'fastify-plugin';
 import jwt from 'jsonwebtoken';
 import { UnauthorizedError } from '../shared/errors.js';
 import type { Env } from '../config/env.js';
 
 declare module 'fastify' {
+  interface FastifyInstance {
+    authenticate: (request: FastifyRequest, reply: FastifyReply) => Promise<void>;
+  }
   interface FastifyRequest {
     userId: string;
     userEmail?: string;
   }
 }
 
-export async function authPlugin(app: FastifyInstance) {
+export const authPlugin = fp(async function (app: FastifyInstance) {
   const env = app.env as Env;
 
   app.decorate('authenticate', async function (request: FastifyRequest, _reply: FastifyReply) {
@@ -38,8 +42,8 @@ export async function authPlugin(app: FastifyInstance) {
       throw new UnauthorizedError('Invalid or expired token');
     }
   });
-}
+}, { name: 'auth-plugin' });
 
 export async function authenticate(request: FastifyRequest, reply: FastifyReply) {
-  await (request.server as FastifyInstance & { authenticate: (req: FastifyRequest, rep: FastifyReply) => Promise<void> }).authenticate(request, reply);
+  await request.server.authenticate(request, reply);
 }