diff --git a/extension/background.js b/extension/background.js
index dfbef9e..8bc2a05 100644
--- a/extension/background.js
+++ b/extension/background.js
@@ -101,6 +101,26 @@ let forceSyncTimeout = null;
 
 // --- Storage Utils ---
 
+/**
+ * Canonical peer data factory. All peer object construction must go through
+ * here to guarantee a consistent shape with predictable null defaults.
+ * @param {object} raw - Raw data from server event or heartbeat payload.
+ * @returns {object} Normalized peer data object.
+ */
+function createPeerData(raw) {
+    return {
+        peerId:        raw.peerId        || null,
+        username:      raw.username      || null,
+        tabTitle:      raw.tabTitle      || null,
+        mediaTitle:    raw.mediaTitle    || null,
+        playbackState: raw.playbackState || null,
+        currentTime:   raw.currentTime   != null ? raw.currentTime : null,
+        volume:        raw.volume        != null ? raw.volume       : null,
+        muted:         raw.muted         != null ? raw.muted        : null,
+        lastHeartbeat: Date.now()
+    };
+}
+
 async function getPeerId() {
     const data = await chrome.storage.local.get(['peerId']);
     if (data.peerId) return data.peerId;
@@ -413,9 +433,7 @@ function handleServerEvent(event, data) {
             if (storageInitialized) chrome.storage.session.set({ currentRoom });
             addLog(`Joined Room: ${data.roomId}`, 'success');
             chrome.runtime.sendMessage({ type: 'PEER_UPDATE', peers: data.peers }).catch(() => {});
-            
-
-            
+                        
             // Inform Website Bridge & Popup
             const joinStatusMsg = { type: 'JOIN_STATUS', success: true, message: 'Joined' };
             chrome.runtime.sendMessage(joinStatusMsg).catch(() => {});
@@ -506,17 +524,7 @@ function handleServerEvent(event, data) {
                 if (!Array.isArray(currentRoom.peers)) currentRoom.peers = [];
                 if (data.status === 'joined') {
                     if (!currentRoom.peers.find(p => (p.peerId || p) === data.peerId)) {
-                        currentRoom.peers.push({ 
-                            peerId: data.peerId, 
-                            username: data.username, 
-                            tabTitle: data.tabTitle,
-                            mediaTitle: data.mediaTitle || null,
-                            playbackState: data.playbackState || null,
-                            currentTime: data.currentTime != null ? data.currentTime : null,
-                            volume: data.volume != null ? data.volume : null,
-                            muted: data.muted != null ? data.muted : null,
-                            lastHeartbeat: Date.now()
-                        });
+                        currentRoom.peers.push(createPeerData(data));
                         if (storageInitialized) chrome.storage.session.set({ currentRoom });
                         chrome.runtime.sendMessage({ type: 'PEER_UPDATE', peers: currentRoom.peers }).catch(() => {});
                     }
@@ -538,19 +546,9 @@ function handleServerEvent(event, data) {
                             peer.muted = data.muted !== undefined ? data.muted : peer.muted;
                             peer.lastHeartbeat = Date.now();
                         } else {
-                            // Migration: replace string with object
+                            // Migration: replace string peer with normalized object
                             const idx = currentRoom.peers.indexOf(peer);
-                            currentRoom.peers[idx] = { 
-                                peerId: data.peerId, 
-                                username: data.username, 
-                                tabTitle: data.tabTitle,
-                                mediaTitle: data.mediaTitle || null,
-                                playbackState: data.playbackState || null,
-                                currentTime: data.currentTime != null ? data.currentTime : null,
-                                volume: data.volume != null ? data.volume : null,
-                                muted: data.muted != null ? data.muted : null,
-                                lastHeartbeat: Date.now()
-                            };
+                            currentRoom.peers[idx] = createPeerData(data);
                         }
                         if (storageInitialized) chrome.storage.session.set({ currentRoom });
                         chrome.runtime.sendMessage({ type: 'PEER_UPDATE', peers: currentRoom.peers }).catch(() => {});
diff --git a/server/index.js b/server/index.js
index 79bf68c..ed087eb 100644
--- a/server/index.js
+++ b/server/index.js
@@ -200,7 +200,16 @@ io.on('connection', (socket) => {
             return;
         }
         if (!payload || typeof payload.roomId !== 'string') return;
-        const { roomId, password, peerId, username, tabTitle, mediaTitle, protocolVersion } = payload;
+        const { password, peerId, protocolVersion } = payload;
+
+        // --- M-2: Sanitize and clamp all string fields ---
+        const roomId   = String(payload.roomId   || '').substring(0, 64);
+        const username = typeof payload.username  === 'string' ? payload.username.substring(0, 30)  : null;
+        const tabTitle = typeof payload.tabTitle  === 'string' ? payload.tabTitle.substring(0, 100) : null;
+        const mediaTitle = typeof payload.mediaTitle === 'string' ? payload.mediaTitle.substring(0, 100) : null;
+
+        if (!roomId) return; // Guard: empty after sanitization
+
         try {
             // Protocol check
             if (protocolVersion !== '1.0.0') {
@@ -422,3 +431,23 @@ setInterval(() => {
 httpServer.listen(PORT, () => {
     log('SERVER', `KoalaSync Relay running on port ${PORT}`);
 });
+
+// --- M-4: Graceful Shutdown ---
+function gracefulShutdown(signal) {
+    log('SERVER', `${signal} received — starting graceful shutdown...`);
+    // 1. Notify all connected clients so they can display a meaningful message
+    io.emit(EVENTS.ERROR, { message: 'Server is restarting. Please reconnect in a moment.' });
+    // 2. Stop accepting new HTTP connections
+    httpServer.close(() => {
+        log('SERVER', 'HTTP server closed. Exiting.');
+        process.exit(0);
+    });
+    // 3. Safety net: force-exit after 5s if connections don't drain
+    setTimeout(() => {
+        log('SERVER', 'Force-exit after timeout.');
+        process.exit(1);
+    }, 5000);
+}
+
+process.on('SIGTERM', () => gracefulShutdown('SIGTERM'));
+process.on('SIGINT',  () => gracefulShutdown('SIGINT'));