fix(lint): resolve ESLint errors in PR-changed files

- event.ts: move type imports to 'type' group (last), alphabetize
  parent group (slug.js before validations); wrap app.authenticate
  calls in arrow functions to satisfy unbound-method rule
- event.test.ts: reorder external/type imports alphabetically;
  add required braces around single-statement if bodies
- slug.ts: replace .substring() with .slice() per unicorn rule

Author: Ridanshi

apps/backend/src/__tests__/event.test.ts

@@ -1,8 +1,11 @@
+import Fastify from 'fastify';
 import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
-import Fastify, { FastifyInstance } from 'fastify';
-import { PrismaClient } from '@prisma/client';
+
 import { eventRoutes } from '../routes/event.js';
 
+import type { PrismaClient } from '@prisma/client';
+import type { FastifyInstance } from 'fastify';
+
 // ─── Shared mock data ────────────────────────────────────────────────────────
 
 const MOCK_USER_ID = 'user-uuid-001';
@@ -320,7 +323,7 @@ describe('Events API', () => {
       let callCount = 0;
       prismaMock.event.create.mockImplementation(async (args: any) => {
         callCount++;
-        if (callCount % 2 === 1) throw conflictError; // odd calls fail
+        if (callCount % 2 === 1) { throw conflictError; } // odd calls fail
         return { ...MOCK_EVENT, slug: args.data.slug };
       });
 
@@ -800,7 +803,7 @@ describe('Events API', () => {
       let callCount = 0;
       prismaMock.event.create.mockImplementation(async (args: any) => {
         callCount++;
-        if (callCount === 1) throw conflictError;
+        if (callCount === 1) { throw conflictError; }
         return { ...MOCK_EVENT, slug: args.data.slug };
       });
 

apps/backend/src/routes/event.ts

@@ -1,6 +1,7 @@
-import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
-import { createEventSchema } from '../validations/event.validation.js';
 import { generateUniqueSlug } from '../utils/slug.js';
+import { createEventSchema } from '../validations/event.validation.js';
+
+import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
 
 const MAX_CREATE_ATTEMPTS = 5;
 
@@ -59,7 +60,7 @@ type EventWithAttendees = {
 export async function eventRoutes(app: FastifyInstance) {
   app.post(
     '/',
-    { preHandler: [app.authenticate] },
+    { preHandler: [(req, reply) => app.authenticate(req, reply)] },
     async (
       request: FastifyRequest<{
         Body: {
@@ -166,7 +167,7 @@ export async function eventRoutes(app: FastifyInstance) {
 
   app.post(
     '/:slug/join',
-    { preHandler: [app.authenticate] },
+    { preHandler: [(req, reply) => app.authenticate(req, reply)] },
     async (request: FastifyRequest<{ Params: { slug: string } }>, reply: FastifyReply) => {
       const userId = (request.user as { id: string }).id;
       const paramsSlug = request.params.slug;
@@ -197,7 +198,7 @@ export async function eventRoutes(app: FastifyInstance) {
 
   app.delete(
     '/:slug/leave',
-    { preHandler: [app.authenticate] },
+    { preHandler: [(req, reply) => app.authenticate(req, reply)] },
     async (request: FastifyRequest<{ Params: { slug: string } }>, reply: FastifyReply) => {
       const userId = (request.user as { id: string }).id;
       const paramsSlug = request.params.slug;

apps/backend/src/utils/slug.ts

@@ -30,13 +30,13 @@ export async function generateUniqueSlug(
     if (!(await slugExists(candidate))) {
       return candidate;
     }
-    const suffix = Math.random().toString(36).substring(2, 6);
+    const suffix = Math.random().toString(36).slice(2, 6);
     candidate = `${cleanSlug}-${suffix}`;
   }
 
   // Last-ditch: append a longer random suffix to maximise the chance of a
   // unique value while keeping a deterministic upper bound on retries.
-  const fallback = `${cleanSlug}-${Math.random().toString(36).substring(2, 10)}`;
+  const fallback = `${cleanSlug}-${Math.random().toString(36).slice(2, 10)}`;
   if (!(await slugExists(fallback))) {
     return fallback;
   }