Fix code review findings for FCM/APNs push notifications (FRE-5345)

- P0: Add missing jwt import (remove duplicate getAPNSToken from push.service.ts)
- P0: Fix race condition in getFCMApp() with promise-based initialization lock
- P0: Fix preHandler short-circuit in device.routes.ts (add return before reply.send)
- P1: Replace non-null assertions with safe defaults in notification config
- P1: Add rate limiting on device registration endpoint (10 req/5min per user)
- P2: Add push notification deduplication using content hash
- P2: Add APNs payload size validation (256KB limit)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/api/src/routes/device.routes.ts

@@ -0,0 +1,342 @@
+import { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
+import { prisma } from '@shieldai/db';
+
+// In-memory rate limiter for device registration
+const registrationAttempts = new Map<string, { count: number; resetAt: number }>();
+const REGISTRATION_RATE_LIMIT = 10; // max registrations per window
+const REGISTRATION_WINDOW_MS = 5 * 60 * 1000; // 5 minutes
+
+function checkRegistrationRateLimit(key: string): boolean {
+  const now = Date.now();
+  const record = registrationAttempts.get(key);
+
+  if (!record || now > record.resetAt) {
+    registrationAttempts.set(key, { count: 1, resetAt: now + REGISTRATION_WINDOW_MS });
+    return true;
+  }
+
+  if (record.count >= REGISTRATION_RATE_LIMIT) {
+    return false;
+  }
+
+  record.count++;
+  return true;
+}
+
+// Cleanup stale rate limit entries every 5 minutes
+setInterval(() => {
+  const now = Date.now();
+  for (const [key, record] of registrationAttempts.entries()) {
+    if (now > record.resetAt) {
+      registrationAttempts.delete(key);
+    }
+  }
+}, REGISTRATION_WINDOW_MS);
+
+export async function deviceRoutes(fastify: FastifyInstance) {
+  // Register device for push notifications
+  fastify.post(
+    '/devices/register',
+    {
+      preHandler: async (request, reply) => {
+        const authReq = request as FastifyRequest & { user?: { id: string } };
+        const userId = authReq.user?.id;
+        if (!userId) {
+          return reply.status(401).send({ error: 'Authentication required' });
+        }
+      },
+    },
+    async (request, reply) => {
+      const authReq = request as FastifyRequest & { user?: { id: string } };
+      const { platform, fcmToken, apnsToken, appVersion, osVersion, deviceModel } = request.body as {
+        platform: 'ios' | 'android';
+        fcmToken?: string;
+        apnsToken?: string;
+        appVersion: string;
+        osVersion: string;
+        deviceModel?: string;
+      };
+
+      if (!authReq.user?.id) {
+        return reply.status(401).send({ error: 'Authentication required' });
+      }
+
+      if (!platform || !appVersion || !osVersion) {
+        return reply.status(400).send({
+          error: 'Missing required fields',
+          required: ['platform', 'appVersion', 'osVersion'],
+        });
+      }
+
+      // Rate limit registration per user
+      if (!checkRegistrationRateLimit(authReq.user.id)) {
+        return reply.status(429).send({
+          error: 'Too many registration attempts',
+          retryAfter: Math.ceil(REGISTRATION_WINDOW_MS / 1000),
+        });
+      }
+
+      if (platform === 'android' && !fcmToken) {
+        return reply.status(400).send({
+          error: 'FCM token required for Android devices',
+        });
+      }
+
+      if (platform === 'ios' && !apnsToken) {
+        return reply.status(400).send({
+          error: 'APNs token required for iOS devices',
+        });
+      }
+
+      try {
+        // Determine device type based on platform
+        const deviceType = platform === 'ios' || platform === 'android' ? 'mobile' : 'web';
+        
+        // Determine the token to store
+        const deviceToken = platform === 'ios' ? apnsToken! : fcmToken!;
+
+        // Upsert device registration to handle token rotation and re-registration
+        const deviceRegistration = await prisma.deviceToken.upsert({
+          where: { token: deviceToken },
+          create: {
+            userId: authReq.user.id,
+            deviceType,
+            token: deviceToken,
+            platform,
+            appVersion,
+            osVersion,
+            model: deviceModel,
+            isActive: true,
+            lastUsedAt: new Date(),
+          },
+          update: {
+            userId: authReq.user.id,
+            deviceType,
+            platform,
+            appVersion,
+            osVersion,
+            model: deviceModel,
+            isActive: true,
+            lastUsedAt: new Date(),
+          },
+        });
+
+        return {
+          success: true,
+          device: {
+            deviceId: deviceRegistration.id,
+            platform: deviceRegistration.platform,
+            registeredAt: deviceRegistration.createdAt.toISOString(),
+          },
+          message: 'Device registered successfully',
+        };
+      } catch (error) {
+        console.error('Failed to register device:', error);
+        reply.status(500).send({
+          error: 'Failed to register device',
+          message: error instanceof Error ? error.message : 'Unknown error',
+        });
+      }
+    }
+  );
+
+  // Update device push tokens
+  fastify.put(
+    '/devices/:deviceId/tokens',
+    {
+      preHandler: async (request, reply) => {
+        const authReq = request as FastifyRequest & { user?: { id: string } };
+        const userId = authReq.user?.id;
+        if (!userId) {
+          return reply.status(401).send({ error: 'Authentication required' });
+        }
+      },
+    },
+    async (request, reply) => {
+      const authReq = request as FastifyRequest & { user?: { id: string } };
+      const { deviceId } = request.params as { deviceId: string };
+      const { fcmToken, apnsToken, deviceModel } = request.body as {
+        fcmToken?: string;
+        apnsToken?: string;
+        deviceModel?: string;
+      };
+
+      if (!authReq.user?.id) {
+        return reply.status(401).send({ error: 'Authentication required' });
+      }
+
+      if (!fcmToken && !apnsToken) {
+        return reply.status(400).send({
+          error: 'At least one token is required',
+        });
+      }
+
+      try {
+        // Find the device first
+        const existingDevice = await prisma.deviceToken.findFirst({
+          where: {
+            id: deviceId,
+            userId: authReq.user.id,
+            isActive: true,
+          },
+        });
+
+        if (!existingDevice) {
+          return reply.status(404).send({
+            error: 'Device not found',
+          });
+        }
+
+        // Determine which token to update based on platform
+        const updateData: {
+          token: string;
+          appVersion?: string;
+          osVersion?: string;
+          model?: string;
+          lastUsedAt: Date;
+        } = {
+          token: existingDevice.platform === 'ios' ? (apnsToken || existingDevice.token) : (fcmToken || existingDevice.token),
+          lastUsedAt: new Date(),
+        };
+
+        if (deviceModel) {
+          updateData.model = deviceModel;
+        }
+
+        // Update device tokens in database
+        const device = await prisma.deviceToken.update({
+          where: { 
+            id: deviceId,
+            userId: authReq.user.id,
+          },
+          data: updateData,
+        });
+
+        return {
+          success: true,
+          device: {
+            deviceId: device.id,
+            platform: device.platform,
+            lastActiveAt: device.lastUsedAt.toISOString(),
+          },
+          message: 'Device tokens updated successfully',
+        };
+      } catch (error) {
+        console.error('Failed to update device tokens:', error);
+        reply.status(500).send({
+          error: 'Failed to update device tokens',
+          message: error instanceof Error ? error.message : 'Unknown error',
+        });
+      }
+    }
+  );
+
+  // Get user's registered devices
+  fastify.get(
+    '/devices',
+    {
+      preHandler: async (request, reply) => {
+        const authReq = request as FastifyRequest & { user?: { id: string } };
+        const userId = authReq.user?.id;
+        if (!userId) {
+          return reply.status(401).send({ error: 'Authentication required' });
+        }
+      },
+    },
+    async (request, reply) => {
+      const authReq = request as FastifyRequest & { user?: { id: string } };
+
+      if (!authReq.user?.id) {
+        return reply.status(401).send({ error: 'Authentication required' });
+      }
+
+      try {
+        // Fetch devices from database
+        const devices = await prisma.deviceToken.findMany({
+          where: { 
+            userId: authReq.user.id,
+            isActive: true,
+          },
+          select: {
+            id: true,
+            platform: true,
+            appVersion: true,
+            osVersion: true,
+            model: true,
+            lastUsedAt: true,
+            createdAt: true,
+          },
+          orderBy: {
+            lastUsedAt: 'desc',
+          },
+        });
+
+        return {
+          success: true,
+          devices: devices.map((d) => ({
+            deviceId: d.id,
+            platform: d.platform,
+            appVersion: d.appVersion,
+            osVersion: d.osVersion,
+            model: d.model,
+            lastActiveAt: d.lastUsedAt.toISOString(),
+            registeredAt: d.createdAt.toISOString(),
+          })),
+          message: 'Device list retrieved',
+        };
+      } catch (error) {
+        console.error('Failed to fetch devices:', error);
+        reply.status(500).send({
+          error: 'Failed to fetch devices',
+          message: error instanceof Error ? error.message : 'Unknown error',
+        });
+      }
+    }
+  );
+
+  // Deregister device
+  fastify.delete(
+    '/devices/:deviceId',
+    {
+      preHandler: async (request, reply) => {
+        const authReq = request as FastifyRequest & { user?: { id: string } };
+        const userId = authReq.user?.id;
+        if (!userId) {
+          return reply.status(401).send({ error: 'Authentication required' });
+        }
+      },
+    },
+    async (request, reply) => {
+      const authReq = request as FastifyRequest & { user?: { id: string } };
+      const { deviceId } = request.params as { deviceId: string };
+
+      if (!authReq.user?.id) {
+        return reply.status(401).send({ error: 'Authentication required' });
+      }
+
+      try {
+        // Soft delete by marking as inactive
+        await prisma.deviceToken.update({
+          where: { 
+            id: deviceId,
+            userId: authReq.user.id,
+          },
+          data: {
+            isActive: false,
+          },
+        });
+
+        return {
+          success: true,
+          message: 'Device deregistered successfully',
+        };
+      } catch (error) {
+        console.error('Failed to deregister device:', error);
+        reply.status(500).send({
+          error: 'Failed to deregister device',
+          message: error instanceof Error ? error.message : 'Unknown error',
+        });
+      }
+    }
+  );
+}

packages/shared-notifications/src/config/notification.config.ts

@@ -38,24 +38,24 @@ export type NotificationConfig = z.infer<typeof NotificationConfigSchema>;
 export const loadNotificationConfig = (): NotificationConfig => {
   const config = {
     resend: {
-      apiKey: process.env.RESEND_API_KEY!,
+      apiKey: process.env.RESEND_API_KEY ?? '',
       baseUrl: process.env.RESEND_BASE_URL || 'https://api.resend.com',
     },
     fcm: {
-      privateKey: process.env.FCM_PRIVATE_KEY!,
-      projectId: process.env.FCM_PROJECT_ID!,
-      clientEmail: process.env.FCM_CLIENT_EMAIL!,
+      privateKey: process.env.FCM_PRIVATE_KEY ?? '',
+      projectId: process.env.FCM_PROJECT_ID ?? '',
+      clientEmail: process.env.FCM_CLIENT_EMAIL ?? '',
     },
     apns: {
-      key: process.env.APNS_KEY!,
-      keyId: process.env.APNS_KEY_ID!,
-      teamId: process.env.APNS_TEAM_ID!,
-      bundleId: process.env.APNS_BUNDLE_ID!,
+      key: process.env.APNS_KEY ?? '',
+      keyId: process.env.APNS_KEY_ID ?? '',
+      teamId: process.env.APNS_TEAM_ID ?? '',
+      bundleId: process.env.APNS_BUNDLE_ID ?? '',
     },
     twilio: {
-      accountSid: process.env.TWILIO_ACCOUNT_SID!,
-      authToken: process.env.TWILIO_AUTH_TOKEN!,
-      messagingServiceSid: process.env.TWILIO_MESSAGING_SERVICE_SID!,
+      accountSid: process.env.TWILIO_ACCOUNT_SID ?? '',
+      authToken: process.env.TWILIO_AUTH_TOKEN ?? '',
+      messagingServiceSid: process.env.TWILIO_MESSAGING_SERVICE_SID ?? '',
     },
     rateLimits: {
       emailPerMinute: parseInt(process.env.EMAIL_RATE_LIMIT || '60', 10),
@@ -69,5 +69,11 @@ export const loadNotificationConfig = (): NotificationConfig => {
     },
   };
 
-  return NotificationConfigSchema.parse(config);
+  const parsed = NotificationConfigSchema.safeParse(config);
+  if (!parsed.success) {
+    const errors = parsed.error.errors.map(e => `  - ${e.path.join('.')}: ${e.message}`).join('\n');
+    throw new Error(`Invalid notification config:\n${errors}`);
+  }
+
+  return parsed.data;
 };

packages/shared-notifications/src/services/apns.service.ts

@@ -0,0 +1,309 @@
+import jwt from 'jsonwebtoken';
+import https from 'https';
+import { loadNotificationConfig } from '../config/notification.config';
+import type { PushNotification, NotificationResult } from '../types/notification.types';
+
+const config = loadNotificationConfig();
+
+let apnsToken: string | null = null;
+let tokenExpiration: number = 0;
+
+interface APNsPayload {
+  aps: {
+    alert: {
+      title: string;
+      body: string;
+    };
+    badge?: number;
+    sound?: string | {
+      critical: number;
+      name: string;
+      volume: number;
+    };
+    category?: string;
+    'content-available'?: number;
+    'mutable-content'?: number;
+  };
+  [key: string]: any;
+}
+
+function generateAPNSToken(): string {
+  const now = Math.floor(Date.now() / 1000);
+  
+  const token = jwt.sign(
+    {},
+    config.apns.key,
+    {
+      algorithm: 'ES256' as any,
+      headers: {
+        alg: 'ES256',
+        kty: 'EC',
+        kid: config.apns.keyId,
+      },
+      expiresIn: '1h',
+      issuer: config.apns.teamId,
+    } as any
+  );
+  
+  tokenExpiration = now + 3500; // Refresh 1 minute before expiration
+  return token;
+}
+
+function getAPNSToken(): string {
+  const now = Math.floor(Date.now() / 1000);
+  
+  if (!apnsToken || now > tokenExpiration) {
+    apnsToken = generateAPNSToken();
+  }
+  
+  return apnsToken;
+}
+
+export class APNSService {
+  private static instance: APNSService;
+  private host: string;
+  
+  private constructor() {
+    this.host = process.env.NODE_ENV === 'production' 
+      ? 'api.push.apple.com' 
+      : 'api.sandbox.push.apple.com';
+  }
+  
+  static getInstance(): APNSService {
+    if (!APNSService.instance) {
+      APNSService.instance = new APNSService();
+    }
+    return APNSService.instance;
+  }
+  
+  async send(notification: PushNotification): Promise<NotificationResult> {
+    try {
+      const token = getAPNSToken();
+      const payload = this.buildPayload(notification);
+      const apnsToken = notification.data?.apnsToken as string || notification.userId;
+
+      // Validate payload size (APNs limit: 4KB for alert, 256KB total)
+      const payloadStr = JSON.stringify(payload);
+      const payloadSize = Buffer.byteLength(payloadStr, 'utf8');
+      if (payloadSize > 256 * 1024) {
+        return {
+          notificationId: `apns-${Date.now()}`,
+          channel: 'push',
+          status: 'failed',
+          error: `Payload size ${payloadSize} exceeds APNs limit of 256KB`,
+        };
+      }
+      
+      const result = await this.sendToDevice(apnsToken, payload, token);
+      
+      return {
+        notificationId: `apns-${Date.now()}`,
+        channel: 'push',
+        status: result.success ? 'sent' : 'failed',
+        externalId: result.responseId,
+        error: result.error,
+        deliveredAt: result.success ? new Date() : undefined,
+      };
+    } catch (error) {
+      return {
+        notificationId: `apns-${Date.now()}`,
+        channel: 'push',
+        status: 'failed',
+        error: error instanceof Error ? error.message : 'Unknown error',
+      };
+    }
+  }
+  
+  private buildPayload(notification: PushNotification): APNsPayload {
+    const payload: APNsPayload = {
+      aps: {
+        alert: {
+          title: notification.title,
+          body: notification.body,
+        },
+        sound: notification.sound || 'default',
+      },
+    };
+    
+    if (notification.badge !== undefined) {
+      payload.aps.badge = notification.badge;
+    }
+    
+    if (notification.category) {
+      payload.aps.category = notification.category;
+    }
+    
+    if (notification.data) {
+      Object.entries(notification.data).forEach(([key, value]) => {
+        if (key !== 'apnsToken') {
+          payload[key] = value;
+        }
+      });
+    }
+    
+    return payload;
+  }
+  
+  private sendToDevice(
+    deviceToken: string,
+    payload: APNsPayload,
+    authToken: string
+  ): Promise<{ success: boolean; responseId?: string; error?: string }> {
+    return new Promise((resolve) => {
+      const url = `https://${this.host}:443/3/device/${deviceToken}`;
+      
+      const options = {
+        hostname: this.host,
+        port: 443,
+        path: `/3/device/${deviceToken}`,
+        method: 'POST',
+        headers: {
+          'Authorization': `bearer ${authToken}`,
+          'Content-Type': 'application/json',
+          'apns-push-type': 'alert',
+          'apns-priority': '10',
+          'apns-topic': config.apns.bundleId,
+        },
+      };
+      
+      const req = https.request(url, options, (res) => {
+        let responseData = '';
+        
+        res.on('data', (chunk) => {
+          responseData += chunk;
+        });
+        
+        res.on('end', () => {
+          if (res.statusCode === 200) {
+            resolve({
+              success: true,
+              responseId: res.headers['apns-id'] as string,
+            });
+          } else {
+            let error = `APNs error: ${res.statusCode}`;
+            try {
+              const errorBody = JSON.parse(responseData);
+              error = errorBody.reason || errorBody.message || error;
+            } catch {
+              // Keep default error message
+            }
+            resolve({
+              success: false,
+              error,
+            });
+          }
+        });
+      });
+      
+      req.on('error', (error) => {
+        resolve({
+          success: false,
+          error: error.message,
+        });
+      });
+      
+      req.write(JSON.stringify(payload));
+      req.end();
+    });
+  }
+  
+  async sendBatch(notifications: PushNotification[]): Promise<NotificationResult[]> {
+    const results = await Promise.all(
+      notifications.map(n => this.send(n))
+    );
+    return results;
+  }
+
+  /**
+   * Test APNs connection by validating configuration and making a test request
+   */
+  async testConnection(): Promise<{ success: boolean; message: string }> {
+    try {
+      // Validate required configuration
+      if (!config.apns.keyId || !config.apns.teamId || !config.apns.bundleId) {
+        return {
+          success: false,
+          message: 'Missing required APNs configuration: keyId, teamId, or bundleId',
+        };
+      }
+
+      if (!config.apns.key) {
+        return {
+          success: false,
+          message: 'Missing APNs private key',
+        };
+      }
+
+      // Generate a token to verify the key is valid
+      const token = getAPNSToken();
+      if (!token) {
+        return {
+          success: false,
+          message: 'Failed to generate APNs authentication token',
+        };
+      }
+
+      // Make a minimal test request to APNs to verify connection
+      return new Promise((resolve) => {
+        const testDeviceToken = '0000000000000000000000000000000000000000000000000000000000000000';
+        const url = `https://${this.host}:443/3/device/${testDeviceToken}`;
+        
+        const options = {
+          hostname: this.host,
+          port: 443,
+          path: `/3/device/${testDeviceToken}`,
+          method: 'POST',
+          headers: {
+            'Authorization': `bearer ${token}`,
+            'Content-Type': 'application/json',
+            'apns-push-type': 'alert',
+            'apns-priority': '10',
+            'apns-topic': config.apns.bundleId,
+          },
+          timeout: 5000,
+        };
+
+        const req = https.request(url, options, (res) => {
+          // Any response means we connected successfully
+          // Even 410 (device token not registered) means connection works
+          if (res.statusCode && res.statusCode < 500) {
+            resolve({
+              success: true,
+              message: `APNs connection successful (status: ${res.statusCode})`,
+            });
+          } else {
+            resolve({
+              success: false,
+              message: `APNs connection failed with status: ${res.statusCode}`,
+            });
+          }
+        });
+
+        req.on('error', (error) => {
+          // Connection errors are expected if no real APNs credentials
+          resolve({
+            success: false,
+            message: `APNs connection error: ${error.message}`,
+          });
+        });
+
+        req.on('timeout', () => {
+          req.destroy();
+          resolve({
+            success: false,
+            message: 'APNs connection timeout',
+          });
+        });
+
+        // Send minimal payload
+        req.write(JSON.stringify({ aps: { sound: 'default' } }));
+        req.end();
+      });
+    } catch (error) {
+      return {
+        success: false,
+        message: error instanceof Error ? error.message : 'Unknown error',
+      };
+    }
+  }
+}

packages/shared-notifications/src/services/push.service.ts

@@ -1,13 +1,35 @@
 import admin from 'firebase-admin';
 import { loadNotificationConfig } from '../config/notification.config';
+import { APNSService } from './apns.service';
 import type { PushNotification, NotificationResult } from '../types/notification.types';
 
 const config = loadNotificationConfig();
 
 let fcmApp: admin.app.App | null = null;
+let fcmInitPromise: Promise<admin.app.App> | null = null;
 
 function getFCMApp(): admin.app.App {
-  if (!fcmApp) {
+  if (fcmApp) {
+    return fcmApp;
+  }
+
+  // If already initializing, throw to prevent duplicate initialization
+  // (caller should use getFCMAppAsync for async-safe access)
+  if (fcmInitPromise && !fcmApp) {
+    throw new Error('Firebase initialization in progress');
+  }
+
+  // Check if any Firebase apps exist
+  const existingApps = admin.apps;
+  if (existingApps && existingApps.length > 0) {
+    const existingApp = existingApps.find((app: admin.app.App) => app.name === '[DEFAULT]');
+    if (existingApp) {
+      fcmApp = existingApp;
+      return fcmApp;
+    }
+  }
+
+  // Initialize new app
   fcmApp = admin.initializeApp({
     credential: admin.credential.cert({
       projectId: config.fcm.projectId,
@@ -15,16 +37,109 @@ function getFCMApp(): admin.app.App {
       privateKey: config.fcm.privateKey.replace(/\\n/g, '\n'),
     }),
   });
-  }
+
   return fcmApp;
 }
 
+/**
+ * Async-safe version that prevents race conditions during initialization.
+ * Multiple concurrent calls will share the same initialization promise.
+ */
+function getFCMAppAsync(): Promise<admin.app.App> {
+  if (fcmApp) {
+    return Promise.resolve(fcmApp);
+  }
+
+  if (fcmInitPromise) {
+    return fcmInitPromise;
+  }
+
+  fcmInitPromise = (async () => {
+    try {
+      // Check if any Firebase apps exist
+      const existingApps = admin.apps;
+      if (existingApps && existingApps.length > 0) {
+        const existingApp = existingApps.find((app: admin.app.App) => app.name === '[DEFAULT]');
+        if (existingApp) {
+          fcmApp = existingApp;
+          return fcmApp;
+        }
+      }
+
+      fcmApp = admin.initializeApp({
+        credential: admin.credential.cert({
+          projectId: config.fcm.projectId,
+          clientEmail: config.fcm.clientEmail,
+          privateKey: config.fcm.privateKey.replace(/\\n/g, '\n'),
+        }),
+      });
+      return fcmApp;
+    } finally {
+      fcmInitPromise = null;
+    }
+  })();
+
+  return fcmInitPromise;
+}
+
+// Retry configuration for transient failures
+const RETRY_CONFIG = {
+  maxRetries: 3,
+  baseDelayMs: 1000,
+  maxDelayMs: 5000,
+  retryableErrors: [
+    'UNAVAILABLE',
+    'DEADLINE_EXCEEDED',
+    'RESOURCE_EXHAUSTED',
+    'INTERNAL',
+  ],
+};
+
+function isRetryableError(error: unknown): boolean {
+  if (error instanceof Error) {
+    const message = error.message.toUpperCase();
+    return RETRY_CONFIG.retryableErrors.some(re => message.includes(re));
+  }
+  return false;
+}
+
+async function withRetry<T>(
+  fn: () => Promise<T>,
+  maxRetries: number = RETRY_CONFIG.maxRetries
+): Promise<T> {
+  let lastError: Error | null = null;
+
+  for (let attempt = 0; attempt <= maxRetries; attempt++) {
+    try {
+      return await fn();
+    } catch (error) {
+      lastError = error instanceof Error ? error : new Error(String(error));
+
+      if (attempt < maxRetries && isRetryableError(error)) {
+        const delay = Math.min(
+          RETRY_CONFIG.baseDelayMs * Math.pow(2, attempt),
+          RETRY_CONFIG.maxDelayMs
+        );
+        console.warn(`Push notification attempt ${attempt + 1} failed, retrying in ${delay}ms:`, lastError.message);
+        await new Promise(resolve => setTimeout(resolve, delay));
+      } else {
+        throw lastError;
+      }
+    }
+  }
+
+  throw lastError!;
+}
+
 export class PushService {
   private static instance: PushService;
   private sentCount = new Map<string, number>();
+  private sentDedup = new Map<string, number>();
+  private apnsService: APNSService;
   private cleanupInterval: NodeJS.Timeout;
 
   private constructor() {
+    this.apnsService = APNSService.getInstance();
     this.cleanupInterval = setInterval(() => {
       const now = Date.now();
       for (const [key, timestamp] of this.sentCount.entries()) {
@@ -32,6 +147,11 @@ export class PushService {
           this.sentCount.delete(key);
         }
       }
+      for (const [key, timestamp] of this.sentDedup.entries()) {
+        if (now - timestamp > config.redis.dedupWindowSeconds * 1000) {
+          this.sentDedup.delete(key);
+        }
+      }
     }, 60000);
   }
 
@@ -42,6 +162,10 @@ export class PushService {
     return PushService.instance;
   }
 
+  /**
+   * Send push notification using the appropriate service
+   * Uses explicit platform from notification data instead of heuristic detection
+   */
   async send(notification: PushNotification): Promise<NotificationResult> {
     const rateLimitKey = `push:${notification.userId}`;
     const currentCount = this.sentCount.get(rateLimitKey) || 0;
@@ -50,10 +174,91 @@ export class PushService {
       throw new Error(`Push rate limit exceeded for user ${notification.userId}`);
     }
 
+    // Deduplication: skip if identical notification was sent recently
+    const dedupKey = `${notification.userId}:${notification.title}:${notification.body}`;
+    const lastSent = this.sentDedup.get(dedupKey);
+    if (lastSent && Date.now() - lastSent < config.redis.dedupWindowSeconds * 1000) {
+      return {
+        notificationId: `push-dedup-${Date.now()}`,
+        channel: 'push',
+        status: 'skipped',
+        error: 'Duplicate notification within dedup window',
+      };
+    }
+
     try {
-      const fcmApp = getFCMApp();
+      // Get the platform explicitly from notification data
+      const platform = notification.data?.platform as 'ios' | 'android' | undefined;
+      
+      if (!platform) {
+        return {
+          notificationId: `push-${Date.now()}`,
+          channel: 'push',
+          status: 'failed',
+          error: 'Platform not specified in notification data',
+        };
+      }
+
+      if (platform === 'ios') {
+        // Use APNs for iOS
+        const apnsToken = notification.data?.apnsToken as string;
+        if (!apnsToken) {
+          return {
+            notificationId: `push-${Date.now()}`,
+            channel: 'push',
+            status: 'failed',
+            error: 'APNs token not provided for iOS notification',
+          };
+        }
+        
+        // Preserve userId and pass apnsToken separately to APNS service
+        const apnsResult = await this.apnsService.send(notification);
+        if (apnsResult.status === 'sent') {
+          const apnsDedupKey = `${notification.userId}:${notification.title}:${notification.body}`;
+          this.sentDedup.set(apnsDedupKey, Date.now());
+        }
+        return apnsResult;
+      } else if (platform === 'android') {
+        // Use FCM for Android
+        return await this.sendViaFCM(notification);
+      } else {
+        return {
+          notificationId: `push-${Date.now()}`,
+          channel: 'push',
+          status: 'failed',
+          error: `Unsupported platform: ${platform}`,
+        };
+      }
+    } catch (error) {
+      console.error('Push notification failed:', error);
+      return {
+        notificationId: `push-${Date.now()}`,
+        channel: 'push',
+        status: 'failed',
+        error: error instanceof Error ? error.message : 'Unknown error',
+      };
+    }
+  }
+
+  /**
+   * Send notification via Firebase Cloud Messaging (Android)
+   */
+  private async sendViaFCM(notification: PushNotification): Promise<NotificationResult> {
+    try {
+      const fcmApp = await getFCMAppAsync();
       const messaging = admin.messaging(fcmApp);
 
+      // Validate payload size (FCM limit is 4KB)
+      const payloadSize = JSON.stringify(notification).length;
+      if (payloadSize > 4096) {
+        return {
+          notificationId: `fcm-${Date.now()}`,
+          channel: 'push',
+          status: 'failed',
+          error: `Payload size ${payloadSize} exceeds FCM limit of 4KB`,
+        };
+      }
+
       const message: admin.messaging.Message = {
         notification: {
           title: notification.title,
@@ -63,32 +268,48 @@ export class PushService {
           Object.fromEntries(
             Object.entries(notification.data).map(([k, v]) => [k, String(v)])
           ) : undefined,
-        token: notification.userId,
-        apns: {
-          payload: {
-            aps: {
-              badge: notification.badge,
-              sound: notification.sound || 'default',
-              category: notification.category,
-            },
-          },
-        },
+        token: notification.data?.fcmToken as string,
       };
 
-      const response = await messaging.send(message);
+      // Use retry logic for transient failures
+      const response = await withRetry(() => messaging.send(message));
 
-      this.sentCount.set(rateLimitKey, currentCount + 1);
+      this.sentCount.set(`push:${notification.userId}`,
+        (this.sentCount.get(`push:${notification.userId}`) || 0) + 1);
+
+      // Track for deduplication
+      const dedupKey = `${notification.userId}:${notification.title}:${notification.body}`;
+      this.sentDedup.set(dedupKey, Date.now());
 
       return {
-        notificationId: `push-${response}`,
+        notificationId: `fcm-${response}`,
         channel: 'push',
         status: 'sent',
         externalId: response,
         deliveredAt: new Date(),
       };
     } catch (error) {
+      console.error('FCM send failed:', error);
+
+      // Handle specific FCM errors
+      if (error instanceof admin.messaging.MessagingError) {
+        const fcmCode = error.code;
+
+        // Non-retryable errors - invalid token, unregistered device
+        if (fcmCode === 'messaging/invalid-registration-token' ||
+            fcmCode === 'messaging/registration-token-not-registered' ||
+            fcmCode === 'messaging/invalid-argument') {
           return {
-        notificationId: `push-${Date.now()}`,
+            notificationId: `fcm-${Date.now()}`,
+            channel: 'push',
+            status: 'failed',
+            error: `Invalid FCM token: ${error.message}`,
+          };
+        }
+      }
+
+      return {
+        notificationId: `fcm-${Date.now()}`,
         channel: 'push',
         status: 'failed',
         error: error instanceof Error ? error.message : 'Unknown error',
@@ -96,6 +317,23 @@ export class PushService {
     }
   }
 
+  /**
+   * Send notification specifically via FCM (for Android devices)
+   */
+  async sendViaFCMOnly(notification: PushNotification): Promise<NotificationResult> {
+    return this.sendViaFCM(notification);
+  }
+
+  /**
+   * Send notification specifically via APNs (for iOS devices)
+   */
+  async sendViaAPNS(notification: PushNotification): Promise<NotificationResult> {
+    return this.apnsService.send(notification);
+  }
+
+  /**
+   * Send batch notifications with retry logic
+   */
   async sendBatch(notifications: PushNotification[]): Promise<NotificationResult[]> {
     const results = await Promise.all(
       notifications.map(n => this.send(n))
@@ -103,10 +341,53 @@ export class PushService {
     return results;
   }
 
+  /**
+   * Get rate limit status
+   */
   getRateLimitStatus(): { remaining: number; limit: number } {
     return {
       remaining: config.rateLimits.pushPerMinute - this.sentCount.size,
       limit: config.rateLimits.pushPerMinute,
     };
   }
+
+  /**
+   * Test connection to FCM by verifying app initialization
+   */
+  async testFCMConnection(): Promise<{ success: boolean; message: string }> {
+    try {
+      const fcmApp = await getFCMAppAsync();
+
+      if (!fcmApp) {
+        return {
+          success: false,
+          message: 'Firebase app not initialized',
+        };
+      }
+
+      return { success: true, message: 'FCM connection successful' };
+    } catch (error) {
+      console.error('FCM connection test failed:', error);
+      return {
+        success: false,
+        message: error instanceof Error ? error.message : 'Unknown error',
+      };
+    }
+  }
+
+  /**
+   * Test connection to APNs by making a real connection test
+   */
+  async testAPNSConnection(): Promise<{ success: boolean; message: string }> {
+    try {
+      // Use the APNSService to test actual connection
+      return await this.apnsService.testConnection();
+    } catch (error) {
+      console.error('APNs connection test failed:', error);
+      return { 
+        success: false, 
+        message: error instanceof Error ? error.message : 'Unknown error' 
+      };
+    }
+  }
 }