diff --git a/backend/src/ws.ts b/backend/src/ws.ts
index f3c42ef..f64b447 100644
--- a/backend/src/ws.ts
+++ b/backend/src/ws.ts
@@ -2,12 +2,12 @@ import { FastifyInstance } from 'fastify';
 import { pool } from './db.js';
 import webpush from 'web-push';
 
-// userId -> Set of WebSocket-like connections
+// uid -> Set of WebSocket-like connections
 export const connections = new Map<string, Set<any>>();
 
-function broadcast(userIds: string[], data: object) {
+function broadcast(uids: string[], data: object) {
   const msg = JSON.stringify(data);
-  for (const uid of userIds) {
+  for (const uid of uids) {
     const sockets = connections.get(uid);
     if (sockets) {
       sockets.forEach((ws: any) => {
@@ -26,9 +26,9 @@ async function getChatMemberIds(chatId: string): Promise<string[]> {
   return rows.map((r: any) => r.user_id);
 }
 
-async function sendPushToOfflineUsers(userIds: string[], payload: object) {
+async function sendPushToOfflineUsers(uids: string[], payload: object) {
   const online = new Set(connections.keys());
-  const offline = userIds.filter(id => !online.has(id));
+  const offline = uids.filter(id => !online.has(id));
   if (offline.length === 0) return;
 
   const { rows } = await pool.query(
@@ -52,23 +52,23 @@ async function sendPushToOfflineUsers(userIds: string[], payload: object) {
 }
 
 export function setupWebSocket(app: FastifyInstance) {
-  (app as any).get('/ws', { websocket: true }, (socket: any, req: any) => {
-    let userId: string | null = null;
-
+  (app as any).get('/ws', { websocket: true }, (connection: any, req: any) => {
+    // @fastify/websocket v8 passes a Duplex stream — actual ws.WebSocket is at connection.socket
+    let uid: string;
     try {
       const token = req.query?.token;
       const decoded = app.jwt.verify<{ id: string }>(token);
-      userId = decoded.id;
+      uid = decoded.id;
     } catch {
-      socket.close(1008, 'Unauthorized');
+      connection.socket.close(1008, 'Unauthorized');
       return;
     }
 
-    const uid = userId;
+    const ws = connection.socket; // actual ws.WebSocket
 
-    // Register connection
+    // Register connection (store ws.WebSocket for broadcast)
     if (!connections.has(uid)) connections.set(uid, new Set());
-    connections.get(uid)!.add(socket);
+    connections.get(uid)!.add(ws);
 
     // Update last_seen + notify online (fire-and-forget)
     pool.query('UPDATE users SET last_seen = NOW() WHERE id = $1', [uid]).catch(() => {});
@@ -79,7 +79,7 @@ export function setupWebSocket(app: FastifyInstance) {
       }
     }).catch(() => {});
 
-    socket.on('message', async (raw: any, isBinary: boolean) => {
+    ws.on('message', async (raw: any, isBinary: boolean) => {
       try {
         const str = isBinary ? raw.toString('utf8') : raw.toString();
         console.log('[WS] received:', str.substring(0, 200));
@@ -87,28 +87,28 @@ export function setupWebSocket(app: FastifyInstance) {
 
         if (type === 'typing') {
           const members = await getChatMemberIds(payload.chatId);
-          broadcast(members.filter(id => id !== userId), {
+          broadcast(members.filter(id => id !== uid), {
             type: 'typing',
-            payload: { chatId: payload.chatId, userId, typing: payload.typing }
+            payload: { chatId: payload.chatId, userId: uid, typing: payload.typing }
           });
         }
 
         if (type === 'read_messages') {
           await pool.query(
             `UPDATE chat_members SET last_read_at = NOW() WHERE chat_id = $1 AND user_id = $2`,
-            [payload.chatId, userId]
+            [payload.chatId, uid]
           );
           const members = await getChatMemberIds(payload.chatId);
-          broadcast(members.filter(id => id !== userId), {
+          broadcast(members.filter(id => id !== uid), {
             type: 'messages_read',
-            payload: { chatId: payload.chatId, userId }
+            payload: { chatId: payload.chatId, userId: uid }
           });
         }
 
         if (type === 'send_message') {
           const { rows: [member] } = await pool.query(
             'SELECT role, can_send_messages FROM chat_members WHERE chat_id = $1 AND user_id = $2',
-            [payload.chatId, userId]
+            [payload.chatId, uid]
           );
           if (!member) return;
 
@@ -120,11 +120,11 @@ export function setupWebSocket(app: FastifyInstance) {
             `INSERT INTO messages (chat_id, sender_id, content, type, reply_to_id)
              VALUES ($1, $2, $3, $4, $5)
              RETURNING *`,
-            [payload.chatId, userId, payload.content, payload.type || 'text', payload.replyToId || null]
+            [payload.chatId, uid, payload.content, payload.type || 'text', payload.replyToId || null]
           );
 
           const { rows: [sender] } = await pool.query(
-            'SELECT id, username, display_name, avatar_color FROM users WHERE id = $1', [userId]
+            'SELECT id, username, display_name, avatar_color FROM users WHERE id = $1', [uid]
           );
 
           const fullMsg = {
@@ -145,7 +145,7 @@ export function setupWebSocket(app: FastifyInstance) {
 
           await pool.query(
             'UPDATE chat_members SET last_read_at = NOW() WHERE chat_id = $1 AND user_id = $2',
-            [payload.chatId, userId]
+            [payload.chatId, uid]
           );
         }
 
@@ -156,9 +156,9 @@ export function setupWebSocket(app: FastifyInstance) {
           if (!msg) return;
 
           const { rows: [member] } = await pool.query(
-            'SELECT role FROM chat_members WHERE chat_id = $1 AND user_id = $2', [msg.chat_id, userId]
+            'SELECT role FROM chat_members WHERE chat_id = $1 AND user_id = $2', [msg.chat_id, uid]
           );
-          if (msg.sender_id !== userId && !['owner', 'admin'].includes(member?.role)) return;
+          if (msg.sender_id !== uid && !['owner', 'admin'].includes(member?.role)) return;
 
           await pool.query('UPDATE messages SET is_deleted = TRUE WHERE id = $1', [payload.messageId]);
           const members = await getChatMemberIds(msg.chat_id);
@@ -169,7 +169,7 @@ export function setupWebSocket(app: FastifyInstance) {
           const { rows: [msg] } = await pool.query(
             'SELECT sender_id, chat_id FROM messages WHERE id = $1', [payload.messageId]
           );
-          if (!msg || msg.sender_id !== userId) return;
+          if (!msg || msg.sender_id !== uid) return;
 
           const { rows: [updated] } = await pool.query(
             `UPDATE messages SET content = $1, is_edited = TRUE, edited_at = NOW() WHERE id = $2
@@ -178,7 +178,7 @@ export function setupWebSocket(app: FastifyInstance) {
           );
 
           const { rows: [sender] } = await pool.query(
-            'SELECT id, username, display_name, avatar_color FROM users WHERE id = $1', [userId]
+            'SELECT id, username, display_name, avatar_color FROM users WHERE id = $1', [uid]
           );
 
           const fullMsg = {
@@ -197,10 +197,10 @@ export function setupWebSocket(app: FastifyInstance) {
       }
     });
 
-    socket.on('close', async () => {
+    ws.on('close', async () => {
       const set = connections.get(uid);
       if (set) {
-        set.delete(socket);
+        set.delete(ws);
         if (set.size === 0) {
           connections.delete(uid);
           await pool.query('UPDATE users SET last_seen = NOW() WHERE id = $1', [uid]);
@@ -210,7 +210,7 @@ export function setupWebSocket(app: FastifyInstance) {
           );
           for (const row of memberChats) {
             const ids = await getChatMemberIds(row.chat_id);
-            broadcast(ids, { type: 'user_online', payload: { userId: uid, online: false } });
+            broadcast(ids, { type: 'user_online', payload: { uid: uid, online: false } });
           }
         }
       }