diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 92172fb..a5dd237 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -17,6 +17,9 @@ All notable changes to the KoalaSync browser extension and relay server.
 
 ## [v2.3.1] — 2026-06-15
 
+### Fixed
+- **Server: Concurrent peer join race condition and teardown error handling**
+
 ### Changed
 - **Server: Smart unhandled rejection handling (exits after 5/min instead of 1)**
 - **Server: Optimized admin health metrics allocation**
diff --git a/extension/background.js b/extension/background.js
index f8c4aa0..9f44a08 100644
--- a/extension/background.js
+++ b/extension/background.js
@@ -176,6 +176,7 @@ let reconnectAttempts = 0;
 let currentServerUrl = null;
 let roomIdleSince = null;
 let lastContentHeartbeatAt = null;
+let connectIntent = false;
 const MAX_RECONNECT_ATTEMPTS = 20;
 const _RECONNECT_BASE_DELAY = 500;
 const _RECONNECT_MAX_DELAY = 5000;
@@ -404,7 +405,12 @@ function clearTargetTabForIdle() {
 
 async function leaveRoomAfterIdleGrace(reason) {
     if (!currentRoom) return;
+    connectIntent = false;
+    reconnectFailed = false;
+    reconnectAttempts = 0;
+    chrome.storage.session.set({ reconnectFailed: false, reconnectAttempts: 0, reconnectStartTime: null });
     emit(EVENTS.LEAVE_ROOM, { peerId });
+    forceDisconnect();
     currentRoom = null;
     currentTabId = null;
     currentTabTitle = null;
@@ -457,7 +463,9 @@ async function connect() {
             addLog('Browser is offline. Waiting...', 'warn');
             broadcastConnectionStatus('offline');
             isConnecting = false;
-            scheduleReconnect();
+            if (currentRoom || connectIntent) {
+                scheduleReconnect();
+            }
             return;
         }
 
@@ -564,25 +572,32 @@ async function connect() {
             isNamespaceJoined = false;
             stopPing();
             
-            isForceSyncInitiator = false;
-            forceSyncAcks.clear();
-            if (forceSyncTimeout) clearTimeout(forceSyncTimeout);
-            chrome.storage.session.set({ 
-                isForceSyncInitiator: false, 
-                forceSyncAcks: [], 
-                forceSyncDeadline: null 
-            }).catch(() => {});
+            if (!connectIntent && !currentRoom) {
+                isForceSyncInitiator = false;
+                forceSyncAcks.clear();
+                if (forceSyncTimeout) clearTimeout(forceSyncTimeout);
+                chrome.storage.session.set({ 
+                    isForceSyncInitiator: false, 
+                    forceSyncAcks: [], 
+                    forceSyncDeadline: null 
+                }).catch(() => {});
+            }
 
             
-            if (currentRoom) {
+            if (currentRoom && !connectIntent) {
                 currentRoom.peers = [];
                 if (storageInitialized) chrome.storage.session.set({ currentRoom }).catch(() => {});
                 chrome.runtime.sendMessage({ type: 'PEER_UPDATE', peers: [] }).catch(() => {});
             }
             broadcastConnectionStatus('disconnected');
-            addLog('Disconnected. Scheduling reconnect...', 'warn');
-            socket = null;
-            scheduleReconnect();
+            if (currentRoom || connectIntent) {
+                addLog('Disconnected. Scheduling reconnect...', 'warn');
+                socket = null;
+                scheduleReconnect();
+            } else {
+                addLog('Disconnected. No active session — staying disconnected.', 'info');
+                socket = null;
+            }
         };
 
         socket.onerror = () => {
@@ -597,7 +612,9 @@ async function connect() {
         const errMsg = (e && e.message) ? e.message : String(e || 'Unknown connection error');
         addLog(errMsg, logType);
         broadcastConnectionStatus('disconnected');
-        scheduleReconnect();
+        if (currentRoom || connectIntent) {
+            scheduleReconnect();
+        }
     }
 }
 
@@ -738,6 +755,9 @@ function sendPing() {
             addLog('Ping timeout reached, force disconnecting to trigger reconnect', 'warn');
             pendingPingT = null;
             forceDisconnect();
+            if (currentRoom || connectIntent) {
+                scheduleReconnect();
+            }
         }
         pingTimeout = null;
     }, 5000);
@@ -836,6 +856,14 @@ function handleServerEvent(event, data) {
             break;
         case EVENTS.ERROR:
             isConnecting = false;
+            // If we get a server error before successfully joining a room,
+            // clear connectIntent to prevent an infinite reconnect loop.
+            if (!currentRoom) {
+                connectIntent = false;
+                if (reconnectTimer) { clearTimeout(reconnectTimer); reconnectTimer = null; }
+                reconnectAttempts = 0;
+                reconnectFailed = false;
+            }
             broadcastConnectionStatus('disconnected');
             addLog(`Server Error: ${data.message}`, 'error');
             chrome.storage.local.get(['browserNotifications', 'locale'], async (settings) => {
@@ -1334,7 +1362,7 @@ chrome.alarms.onAlarm.addListener(async (alarm) => {
     if (alarm.name === 'keepAlive') {
         chrome.storage.session.get('keepAlive', () => {});
         if (!socket || socket.readyState !== WebSocket.OPEN) {
-            if (!reconnectFailed) {
+            if (!reconnectFailed && (currentRoom || connectIntent)) {
                 connect();
             }
         } else if (currentRoom) {
@@ -1417,6 +1445,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
 
     if (message.type === 'CONNECT') {
         const settings = await getSettings();
+        connectIntent = !!settings.roomId;
         const desiredUrl = resolveServerUrl(settings);
 
         if (settings.roomId && currentRoom && currentRoom.roomId === settings.roomId && socket && socket.readyState === WebSocket.OPEN && isNamespaceJoined && desiredUrl === currentServerUrl) {
@@ -1439,7 +1468,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
         }
         if (desiredUrl !== currentServerUrl || !socket || socket.readyState !== WebSocket.OPEN || !isNamespaceJoined) {
             if (desiredUrl !== currentServerUrl) forceDisconnect();
-            connect();
+            if (settings.roomId) connect();
         } else if (settings.roomId) {
             emit(EVENTS.JOIN_ROOM, { 
                 roomId: settings.roomId, 
@@ -1452,6 +1481,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
         }
         sendResponse({ status: 'ok' });
     } else if (message.type === 'RETRY_CONNECT') {
+        connectIntent = true;
         reconnectFailed = false;
         reconnectStartTime = null;
         reconnectAttempts = 0;
@@ -1480,6 +1510,10 @@ async function handleAsyncMessage(message, sender, sendResponse) {
             ping: currentPingMs
         });
     } else if (message.type === 'LEAVE_ROOM') {
+        connectIntent = false;
+        reconnectFailed = false;
+        reconnectAttempts = 0;
+        chrome.storage.session.set({ reconnectFailed: false, reconnectAttempts: 0, reconnectStartTime: null });
         resetAudioProcessingInTab(currentTabId);
         emit(EVENTS.LEAVE_ROOM, { peerId });
         currentRoom = null;
@@ -1510,8 +1544,10 @@ async function handleAsyncMessage(message, sender, sendResponse) {
             episodeLobby: null,
             expectedAcksCount: 0
         });
+        chrome.storage.local.set({ roomId: '', password: '' }).catch(() => {});
         addLog('Left Room', 'info');
         chrome.runtime.sendMessage({ type: 'PEER_UPDATE', peers: [] }).catch(() => {});
+        forceDisconnect();
         sendResponse({ status: 'ok' });
     } else if (message.type === 'CLEAR_LOGS') {
         logs = [];
@@ -1526,6 +1562,16 @@ async function handleAsyncMessage(message, sender, sendResponse) {
     } else if (message.type === 'WEB_JOIN_REQUEST') {
         const { roomId: rawRoomId, password, useCustomServer, serverUrl } = message;
         const roomId = typeof rawRoomId === 'string' ? rawRoomId.replace(/[^a-zA-Z0-9\-]/g, '') : '';
+        if (!roomId) {
+            const errMsg = { type: 'JOIN_STATUS', success: false, message: 'Invalid room ID' };
+            chrome.runtime.sendMessage(errMsg).catch(() => {});
+            chrome.tabs.query({}, (tabs) => {
+                tabs.forEach(tab => chrome.tabs.sendMessage(tab.id, errMsg).catch(() => {}));
+            });
+            sendResponse({ status: 'invalid_room_id' });
+            return;
+        }
+        connectIntent = true;
         chrome.storage.local.set({ 
             roomId, 
             password,
@@ -1541,6 +1587,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
                 for (const tab of tabs) {
                     chrome.tabs.sendMessage(tab.id, { type: 'JOIN_STATUS', success: true, message: 'Already in room' }).catch(() => {});
                 }
+                sendResponse({ status: 'already_joined' });
                 return;
             }
 
@@ -1554,7 +1601,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
             if (desiredUrl !== currentServerUrl || !socket || socket.readyState !== WebSocket.OPEN || !isNamespaceJoined) {
                 if (desiredUrl !== currentServerUrl) forceDisconnect();
                 connect();
-            } else {
+            } else if (roomId) {
                 emit(EVENTS.JOIN_ROOM, { 
                     roomId, 
                     password,
@@ -1939,5 +1986,8 @@ chrome.tabs.onUpdated.addListener(async (tabId, changeInfo, _tab) => {
     }
 });
 
-// Initial Connect
-connect();
+// Initial Connect — only if user has an active room configuration
+getSettings().then(settings => {
+    connectIntent = !!settings.roomId;
+    if (connectIntent) connect();
+}).catch(() => connectIntent = false);
diff --git a/extension/popup.js b/extension/popup.js
index baa6013..4c39bc9 100644
--- a/extension/popup.js
+++ b/extension/popup.js
@@ -237,8 +237,7 @@ async function init() {
     refreshLogs();
     refreshHistory();
 
-    // Default connection status (localized) before async check
-    applyConnectionStatus('disconnected');
+    // Initial Status Check (status shows via GET_STATUS below)
 
     // Initial Status Check
     chrome.runtime.sendMessage({ type: 'GET_STATUS' }, async (res) => {
@@ -255,6 +254,13 @@ async function init() {
             updatePeerList(res.peers);
             lastKnownPeers = res.peers || [];
             if (res.lastActionState) updateLastActionUI(res.lastActionState, res.peers);
+
+            // If user has a room configured but background is not connected,
+            // trigger connection now — the popup opening is explicit user intent.
+            if (res.status === 'disconnected' && localData.roomId) {
+                chrome.runtime.sendMessage({ type: 'CONNECT' }).catch(() => {});
+                applyConnectionStatus('connecting');
+            }
             
             // Populate Tabs using the background's targetTabId
             await populateTabs(res.peers, res.targetTabId);
@@ -1195,11 +1201,23 @@ elements.joinBtn.addEventListener('click', async () => {
     
     if (joinBtnTimeout) clearTimeout(joinBtnTimeout);
     joinBtnTimeout = setTimeout(() => {
-        elements.joinBtn.disabled = false;
-        elements.joinBtn.textContent = getMessage('BTN_JOIN_ROOM');
-        joinBtnTimeout = null;
-        isProcessingConnection = false;
-        showError(getMessage('ERR_CONN_TIMEOUT'));
+        chrome.runtime.sendMessage({ type: 'GET_STATUS' }, (res) => {
+            if (res && res.status === 'connecting') {
+                joinBtnTimeout = setTimeout(() => {
+                    elements.joinBtn.disabled = false;
+                    elements.joinBtn.textContent = getMessage('BTN_JOIN_ROOM');
+                    joinBtnTimeout = null;
+                    isProcessingConnection = false;
+                    showError(getMessage('ERR_CONN_TIMEOUT'));
+                }, 15000);
+                return;
+            }
+            elements.joinBtn.disabled = false;
+            elements.joinBtn.textContent = getMessage('BTN_JOIN_ROOM');
+            joinBtnTimeout = null;
+            isProcessingConnection = false;
+            if (res && res.status !== 'connected') showError(getMessage('ERR_CONN_TIMEOUT'));
+        });
     }, 15000);
     
     const serverUrl = elements.serverUrl.value.trim();
@@ -1210,6 +1228,8 @@ elements.joinBtn.addEventListener('click', async () => {
         showError(getMessage('ERR_INVALID_SERVER_URL'));
         elements.joinBtn.disabled = false;
         elements.joinBtn.textContent = getMessage('BTN_JOIN_ROOM');
+        if (joinBtnTimeout) { clearTimeout(joinBtnTimeout); joinBtnTimeout = null; }
+        isProcessingConnection = false;
         return;
     }
     if (useCustom && serverUrl) {
@@ -1220,6 +1240,7 @@ elements.joinBtn.addEventListener('click', async () => {
             showError(getMessage('ERR_INVALID_SERVER_URL'));
             elements.joinBtn.disabled = false;
             elements.joinBtn.textContent = getMessage('BTN_JOIN_ROOM');
+            if (joinBtnTimeout) { clearTimeout(joinBtnTimeout); joinBtnTimeout = null; }
             isProcessingConnection = false;
             return;
         }
@@ -1608,6 +1629,9 @@ chrome.runtime.onMessage.addListener((msg) => {
         updatePeerList(msg.peers);
         if (msg.peers) detectPeerChanges(msg.peers);
     } else if (msg.type === 'CONNECTION_STATUS') {
+        if (msg.status === 'connected' || msg.status === 'disconnected') {
+            if (joinBtnTimeout) { clearTimeout(joinBtnTimeout); joinBtnTimeout = null; }
+        }
         if (msg.status === 'connected') {
             clearConnectionErrorTimer();
         }