diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 4267f7c..bcf1998 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -4,7 +4,7 @@ All notable changes to the KoalaSync browser extension and relay server.
 
 ---
 
-## Unreleased
+## [v3.0.2] — 2026-07-31
 
 ### Added
 - **Extension: Quick reactions** — Adds six encrypted one-click reactions with a local choice between chat-only display and bounded falling reactions over the video.
@@ -13,6 +13,11 @@ All notable changes to the KoalaSync browser extension and relay server.
 ### Changed
 - **Extension: Real dock behavior** — Anchors the collapsed Koala chat launcher to the selected side, reserves a page column in normal and fullscreen layouts, and clips viewport-bound page layers away from the open dock; detached mode remains freely movable.
 - **Extension: Koala chat launcher** — Replaces the generic speech-bubble emoji with the KoalaSync extension icon plus a chat marker.
+- **Extension: Reliable long chat sends** — Accepts up to 5000 Unicode code points, splits them into at most ten compatible 500-codepoint messages, waits for each relay echo before clearing text, and suppresses chat notifications while the selected video tab is focused.
+
+### Fixed
+- **Extension: Strict target-tab lifecycle** — Fully deactivates playback, audio, heartbeat, observer, seek-bridge, and chat code before changing targets, cleans up superseded injections, and limits website-bridge status delivery to the KoalaSync site instead of broadcasting to every open tab.
+- **Extension: Tab switching and page restore** — Keeps ordinary tab changes idle and injection-free, makes selecting the same target idempotent, blocks delayed callbacks after teardown, and restores the existing target cleanly after Firefox back/forward-cache suspension.
 
 ## [v3.0.1] — 2026-07-26
 
diff --git a/docs/CHAT.md b/docs/CHAT.md
index 66b20d1..3ea550c 100644
--- a/docs/CHAT.md
+++ b/docs/CHAT.md
@@ -49,7 +49,9 @@ the stamped value as AAD.
 
 ## Client policy
 
-- Maximum plaintext length: 500 Unicode code points.
+- Maximum plaintext length per relay message: 500 Unicode code points.
+- The composer accepts up to 5000 Unicode code points and sends them sequentially
+  as at most ten independently encrypted `chat-v1` messages.
 - Decrypted text is untrusted. Escape HTML before applying the supported limited
   Markdown formatting.
 - Quick reactions use the same encrypted message path as text. They remain readable
@@ -84,6 +86,10 @@ the stamped value as AAD.
 - Chat display is a local option and defaults to off. Enabling or disabling it never
   deletes the room chat secret, so it can be enabled later without creating a room.
 - Without the relay `chat` capability, no chat control is shown.
+- System notifications are suppressed while the selected video tab and its browser
+  window are focused.
+- A send succeeds only after the relay echoes the authenticated ciphertext back to
+  the sender. Unconfirmed and remaining split messages stay in the composer.
 
 ## Mixed-version rollout
 
diff --git a/extension/background.js b/extension/background.js
index f98c46c..c945667 100644
--- a/extension/background.js
+++ b/extension/background.js
@@ -6,7 +6,7 @@ import { applyTitlePrivacyToPayload, sanitizeSharedTitle, sanitizeTabTitle, norm
 import { initTabManager } from './modules/tab-manager.js';
 import { clearChatKeyCache, decryptChatMessage, encryptChatMessage, generateChatSecret, validateChatSecret } from './chat-crypto.js';
 import { buildChatRelayPayload, encodeSocketEvent } from './chat-wire.js';
-import { createChatSendLimiter, createLatestTaskQueue, normalizeRoomId } from './chat-session.js';
+import { createChatEchoTracker, createChatSendLimiter, createLatestTaskQueue, normalizeRoomId, shouldShowChatNotification } from './chat-session.js';
 import { createChatActivityStore } from './chat-activity.js';
 import { HOST_ACCESS_REQUIRED_STATUS, normalizeTabId, inspectTabHostAccess, isHostAccessError, addTabHostAccessRequest, removeTabHostAccessRequest } from './host-access.js';
 import './page-api-seek-overrides.js';
@@ -90,6 +90,7 @@ let chatSecretGuard = '';
 let chatSessionGeneration = 0;
 let chatReceiveQueue = Promise.resolve();
 const chatSendLimiter = createChatSendLimiter();
+const chatEchoTracker = createChatEchoTracker();
 const chatActivityStore = createChatActivityStore();
 const webJoinCoordinator = createLatestTaskQueue();
 function serverSupports(cap) { return Array.isArray(serverCapabilities) && serverCapabilities.includes(cap); }
@@ -102,6 +103,7 @@ function invalidateChatSession() {
     chatSessionGeneration++;
     chatReceiveQueue = Promise.resolve();
     chatSendLimiter.reset();
+    chatEchoTracker.reset();
     clearChatKeyCache();
 }
 
@@ -589,7 +591,7 @@ function clearTargetTabForIdle(expectedTabId = null, expectedGeneration = null)
     completeForceSyncBeforeTargetChange(null);
     invalidateTargetActivations();
     clearPendingTarget().catch(() => {});
-    if (currentTabId) chrome.tabs.sendMessage(Number(currentTabId), { type: 'CHAT_DESTROY' }).catch(() => {});
+    if (currentTabId) deactivateTargetTab(currentTabId).catch(() => {});
     currentTabId = null;
     currentTabTitle = null;
     lastContentHeartbeatAt = null;
@@ -625,7 +627,7 @@ async function leaveRoomAfterIdleGrace(reason) {
     // Notify content.js/popup BEFORE currentTabId is cleared so they can reset
     // any stale guest-side HCM state (dialog/badge/desync) — H-2.
     broadcastControlMode();
-    if (currentTabId) chrome.tabs.sendMessage(Number(currentTabId), { type: 'CHAT_DESTROY' }).catch(() => {});
+    if (currentTabId) await deactivateTargetTab(currentTabId);
     invalidateTargetActivations();
     currentTabId = null;
     currentTabTitle = null;
@@ -873,6 +875,21 @@ function broadcastConnectionStatus(status) {
     updateBadgeStatus();
 }
 
+async function broadcastJoinStatus(message, shouldSend = () => true) {
+    let websiteTabs = [];
+    try {
+        websiteTabs = await chrome.tabs.query({ url: 'https://sync.koalastuff.net/*' });
+    } catch (_) {
+        // The website bridge is optional and may be unavailable.
+    }
+    if (!shouldSend()) return false;
+    chrome.runtime.sendMessage(message).catch(() => {});
+    await Promise.all(websiteTabs.map(tab =>
+        chrome.tabs.sendMessage(tab.id, message).catch(() => {})
+    ));
+    return true;
+}
+
 function updateBadgeStatus() {
     const isConnected = socket && socket.readyState === WebSocket.OPEN && isNamespaceJoined;
     const isReconnecting = !isConnected && reconnectAttempts > 0;
@@ -934,9 +951,42 @@ function showNotification(senderName, action) {
     });
 }
 
+function getTabForNotification(tabId) {
+    return new Promise(resolve => {
+        try {
+            chrome.tabs.get(tabId, tab => {
+                if (chrome.runtime.lastError) resolve(null);
+                else resolve(tab || null);
+            });
+        } catch (_) {
+            resolve(null);
+        }
+    });
+}
+
+function getWindowForNotification(windowId) {
+    return new Promise(resolve => {
+        try {
+            chrome.windows.get(windowId, windowInfo => {
+                if (chrome.runtime.lastError) resolve(null);
+                else resolve(windowInfo || null);
+            });
+        } catch (_) {
+            resolve(null);
+        }
+    });
+}
+
 function showChatNotification(displayName, text) {
     chrome.storage.local.get(['chatNotifications', 'locale'], async (settings) => {
-        if (settings.chatNotifications === false) return;
+        const enabled = settings.chatNotifications !== false;
+        if (!enabled) return;
+        const targetTabId = normalizeTabId(currentTabId);
+        const tab = targetTabId === null ? null : await getTabForNotification(targetTabId);
+        const windowInfo = Number.isInteger(tab?.windowId)
+            ? await getWindowForNotification(tab.windowId)
+            : null;
+        if (!shouldShowChatNotification({ enabled, targetTabId, tab, windowInfo })) return;
 
         await loadLocale(settings.locale || getSystemLanguage());
         chrome.notifications.create(`chat_${Date.now()}`, {
@@ -1233,12 +1283,7 @@ async function handleServerEvent(event, data) {
                         
             // Inform Website Bridge & Popup
             const joinStatusMsg = { type: 'JOIN_STATUS', success: true, message: 'Joined' };
-            chrome.runtime.sendMessage(joinStatusMsg).catch(() => {});
-            chrome.tabs.query({}, (tabs) => {
-                tabs.forEach(tab => {
-                    chrome.tabs.sendMessage(tab.id, joinStatusMsg).catch(() => {});
-                });
-            });
+            await broadcastJoinStatus(joinStatusMsg);
             break;
         case EVENTS.CONTROL_MODE:
             // Host Control Mode changed (toggle or host-leave fallback).
@@ -1279,6 +1324,7 @@ async function handleServerEvent(event, data) {
                         secret: chatKey
                     });
                     if (!isCurrentSession() || chatSecretGuard !== chatKey) return;
+                    if (received.senderId === peerId) chatEchoTracker.acknowledge(received.ciphertext);
                     const senderPeer = currentRoom.peers?.find(candidate =>
                         (typeof candidate === 'object' ? candidate.peerId : candidate) === received.senderId
                     );
@@ -1333,12 +1379,7 @@ async function handleServerEvent(event, data) {
             });
             // Inform Website Bridge & Popup
             const errStatusMsg = { type: 'JOIN_STATUS', success: false, message: data.message };
-            chrome.runtime.sendMessage(errStatusMsg).catch(() => {});
-            chrome.tabs.query({}, (tabs) => {
-                tabs.forEach(tab => {
-                    chrome.tabs.sendMessage(tab.id, errStatusMsg).catch(() => {});
-                });
-            });
+            await broadcastJoinStatus(errStatusMsg);
             break;
         case EVENTS.PLAY:
         case EVENTS.PAUSE:
@@ -1896,8 +1937,12 @@ function shouldUsePageApiSeek(url) {
 }
 
 function installPageApiSeekBridge() {
-    if (window.__koalaPageApiSeekBridgeInstalled) return;
-    window.__koalaPageApiSeekBridgeInstalled = true;
+    if (window.__koalaPageApiSeekBridge?.activate) {
+        window.__koalaPageApiSeekBridge.activate();
+        return;
+    }
+
+    let active = true;
 
     function currentMatch() {
         return typeof window.koalaFindPageApiSeekProvider === 'function'
@@ -1933,17 +1978,23 @@ function installPageApiSeekBridge() {
         }
     }
 
-    window.addEventListener('message', (event) => {
+    function handleBridgeMessage(event) {
         if (event.source !== window) return;
         const data = event.data;
-        if (!data || data.__koalaPageApiSeek !== 1 || data.kind !== 'seek' || typeof data.time !== 'number') return;
+        if (!data || data.__koalaPageApiSeek !== 1) return;
+        if (data.kind === 'destroy') {
+            destroy();
+            return;
+        }
+        if (!active || data.kind !== 'seek' || typeof data.time !== 'number') return;
         seekWithPageApi(data.time);
-    });
+    }
 
     // Disney+'s <video> currentTime is blob-relative and its scrubber lags, so
     // the isolated-world content script can't read an accurate position. Push
     // the real playhead/duration (seconds) from the page's media player.
-    setInterval(() => {
+    const timelineInterval = setInterval(() => {
+        if (!active) return;
         try {
             const match = currentMatch();
             if (!match || match.provider !== 'disney') return;
@@ -1961,12 +2012,36 @@ function installPageApiSeekBridge() {
             // Ignore transient errors (player teardown / element swap).
         }
     }, 250);
+
+    function destroy() {
+        if (!active) return;
+        active = false;
+        clearInterval(timelineInterval);
+        window.removeEventListener('message', handleBridgeMessage);
+        delete window.__koalaPageApiSeekBridge;
+    }
+
+    window.addEventListener('message', handleBridgeMessage);
+    window.__koalaPageApiSeekBridge = {
+        activate() {
+            active = true;
+        },
+        destroy
+    };
 }
 
 function setPageApiSeekEnabled(enabled) {
     window.KOALA_PAGE_API_SEEK_ENABLED = enabled === true;
 }
 
+async function deactivateTargetTab(tabId) {
+    const normalizedTabId = normalizeTabId(tabId);
+    if (normalizedTabId === null) return;
+    resetAudioProcessingInTab(normalizedTabId);
+    await chrome.tabs.sendMessage(normalizedTabId, { type: 'TARGET_DEACTIVATE' }).catch(() => {});
+    await chrome.tabs.sendMessage(normalizedTabId, { type: 'CHAT_DESTROY' }).catch(() => {});
+}
+
 function createHostAccessRequiredError(access, requestAdded, cause) {
     const error = new Error(`Host access required for ${access.host || 'this website'}`);
     error.code = HOST_ACCESS_REQUIRED_STATUS;
@@ -2226,10 +2301,19 @@ async function activateTargetTab(tabId, tabTitle, {
     const previousTabId = normalizeTabId(currentTabId);
 
     try {
+        if (previousTabId && previousTabId !== selectedTabId) {
+            await deactivateTargetTab(previousTabId);
+        }
+        if (activationGeneration !== targetActivationGeneration) {
+            return { status: 'superseded' };
+        }
         try {
             await injectContentScript(selectedTabId, { requestHostAccess });
         } catch (error) {
             if (activationGeneration !== targetActivationGeneration) {
+                if (normalizeTabId(currentTabId) !== selectedTabId) {
+                    await deactivateTargetTab(selectedTabId);
+                }
                 if (error?.code === HOST_ACCESS_REQUIRED_STATUS
                     && error.requestAdded === true
                     && activeTargetActivation?.tabId !== selectedTabId) {
@@ -2246,8 +2330,7 @@ async function activateTargetTab(tabId, tabTitle, {
             lastContentHeartbeatAt = null;
             if (currentRoom) roomIdleSince = Date.now();
             if (previousTabId) {
-                resetAudioProcessingInTab(previousTabId);
-                chrome.tabs.sendMessage(previousTabId, { type: 'CHAT_DESTROY' }).catch(() => {});
+                await deactivateTargetTab(previousTabId);
             }
             await chrome.storage.session.set({
                 currentTabId: null,
@@ -2285,33 +2368,29 @@ async function activateTargetTab(tabId, tabTitle, {
         }
 
         if (activationGeneration !== targetActivationGeneration) {
-            if (currentTabId !== selectedTabId) resetAudioProcessingInTab(selectedTabId);
+            if (currentTabId !== selectedTabId) await deactivateTargetTab(selectedTabId);
             return { status: 'superseded' };
         }
 
         await applyAudioSettingsToTab(selectedTabId);
         if (activationGeneration !== targetActivationGeneration) {
-            if (currentTabId !== selectedTabId) resetAudioProcessingInTab(selectedTabId);
+            if (currentTabId !== selectedTabId) await deactivateTargetTab(selectedTabId);
             return { status: 'superseded' };
         }
         await removeTabHostAccessRequest(chrome, selectedTabId);
         if (activationGeneration !== targetActivationGeneration) {
-            if (currentTabId !== selectedTabId) resetAudioProcessingInTab(selectedTabId);
+            if (currentTabId !== selectedTabId) await deactivateTargetTab(selectedTabId);
             return { status: 'superseded' };
         }
         await clearPendingTarget();
         if (activationGeneration !== targetActivationGeneration) {
-            if (currentTabId !== selectedTabId) resetAudioProcessingInTab(selectedTabId);
+            if (currentTabId !== selectedTabId) await deactivateTargetTab(selectedTabId);
             return { status: 'superseded' };
         }
         currentTabId = selectedTabId;
         currentTabTitle = typeof tabTitle === 'string' ? tabTitle : null;
         lastContentHeartbeatAt = null;
         if (currentRoom) roomIdleSince = Date.now();
-        if (previousTabId && previousTabId !== selectedTabId) {
-            resetAudioProcessingInTab(previousTabId);
-            chrome.tabs.sendMessage(previousTabId, { type: 'CHAT_DESTROY' }).catch(() => {});
-        }
         await chrome.storage.session.set({
             currentTabId,
             currentTabTitle,
@@ -2651,10 +2730,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
         if (settings.roomId && currentRoom && currentRoom.roomId === settings.roomId && socket && socket.readyState === WebSocket.OPEN && isNamespaceJoined && desiredUrl === currentServerUrl) {
             broadcastConnectionStatus('connected');
             if (currentTabId) chrome.tabs.sendMessage(Number(currentTabId), { type: 'CHAT_CONTEXT_UPDATE' }).catch(() => {});
-            const tabs = await new Promise(resolve => chrome.tabs.query({}, resolve));
-            for (const tab of tabs) {
-                chrome.tabs.sendMessage(tab.id, { type: 'JOIN_STATUS', success: true, message: 'Already in room' }).catch(() => {});
-            }
+            await broadcastJoinStatus({ type: 'JOIN_STATUS', success: true, message: 'Already in room' });
             if (typeof sendResponse === 'function') sendResponse({ status: 'ok' });
             return;
         }
@@ -2827,8 +2903,19 @@ async function handleAsyncMessage(message, sender, sendResponse) {
                 sendResponse({ status: 'session_changed' });
                 return;
             }
+            const echoPromise = chatEchoTracker.waitFor(ciphertext);
             const sent = emitLive(EVENTS.CHAT_MESSAGE, buildChatRelayPayload(ciphertext));
-            sendResponse({ status: sent ? 'ok' : 'disconnected' });
+            if (!sent) {
+                chatEchoTracker.cancel(ciphertext);
+                sendResponse({ status: 'disconnected' });
+                return;
+            }
+            const acknowledged = await echoPromise;
+            if (!isCurrentSession() || chatSecretGuard !== chatKey) {
+                sendResponse({ status: 'session_changed' });
+                return;
+            }
+            sendResponse({ status: acknowledged ? 'ok' : 'unconfirmed' });
         } catch (err) {
             sendResponse({ status: err instanceof RangeError ? 'too_long' : 'invalid_message' });
         }
@@ -2917,7 +3004,6 @@ async function handleAsyncMessage(message, sender, sendResponse) {
         reconnectFailed = false;
         reconnectAttempts = 0;
         chrome.storage.session.set({ reconnectFailed: false, reconnectAttempts: 0, reconnectStartTime: null });
-        resetAudioProcessingInTab(currentTabId);
         emit(EVENTS.LEAVE_ROOM, { peerId });
         currentRoom = null;
         clearChatActivity();
@@ -2929,7 +3015,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
         // Notify content.js/popup BEFORE currentTabId is cleared so they drop any
         // stale guest-side HCM state (dialog/badge/desync) — H-2/H-3.
         broadcastControlMode();
-        if (currentTabId) chrome.tabs.sendMessage(Number(currentTabId), { type: 'CHAT_DESTROY' }).catch(() => {});
+        if (currentTabId) await deactivateTargetTab(currentTabId);
         invalidateTargetActivations();
         currentTabId = null;
         currentTabTitle = null;
@@ -2984,10 +3070,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
         const chatKey = validateChatSecret(rawChatKey);
         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(() => {}));
-            });
+            await broadcastJoinStatus(errMsg);
             sendResponse({ status: 'invalid_room_id' });
             return;
         }
@@ -3021,14 +3104,14 @@ async function handleAsyncMessage(message, sender, sendResponse) {
                 if (roomId && currentRoom && currentRoom.roomId === roomId && socket && socket.readyState === WebSocket.OPEN && isNamespaceJoined && desiredUrl === currentServerUrl) {
                     broadcastConnectionStatus('connected');
                     if (currentTabId) chrome.tabs.sendMessage(Number(currentTabId), { type: 'CHAT_CONTEXT_UPDATE' }).catch(() => {});
-                    const tabs = await new Promise(resolve => chrome.tabs.query({}, resolve));
-                    if (!isCurrentJoin()) {
+                    const statusSent = await broadcastJoinStatus(
+                        { type: 'JOIN_STATUS', success: true, message: 'Already in room' },
+                        isCurrentJoin
+                    );
+                    if (!statusSent || !isCurrentJoin()) {
                         sendResponse({ status: 'superseded' });
                         return { status: 'superseded' };
                     }
-                    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 { status: 'already_joined' };
                 }
@@ -3382,8 +3465,7 @@ async function handleAsyncMessage(message, sender, sendResponse) {
             lastContentHeartbeatAt = null;
             if (currentRoom) roomIdleSince = Date.now();
             if (previousTabId) {
-                resetAudioProcessingInTab(previousTabId);
-                chrome.tabs.sendMessage(Number(previousTabId), { type: 'CHAT_DESTROY' }).catch(() => {});
+                await deactivateTargetTab(previousTabId);
             }
             await clearPendingTarget();
             await chrome.storage.session.set({
diff --git a/extension/chat-format.js b/extension/chat-format.js
index 766eb40..45b76dd 100644
--- a/extension/chat-format.js
+++ b/extension/chat-format.js
@@ -29,5 +29,41 @@
         return tokens;
     }
 
-    root.KoalaSyncChatFormat = Object.freeze({ escapeChatHtml, formatChatText, tokenizeChatText });
+    function splitChatText(value, maxCodePoints = 500, maxChunks = 10) {
+        if (!Number.isInteger(maxCodePoints) || maxCodePoints < 1 || !Number.isInteger(maxChunks) || maxChunks < 1) {
+            throw new TypeError('Chat chunk limits must be positive integers');
+        }
+        let remaining = [...String(value ?? '').trim()];
+        if (remaining.length === 0) return [];
+        if (remaining.length > maxCodePoints * maxChunks) {
+            throw new RangeError('Chat composer text exceeds the chunk limit');
+        }
+
+        const chunks = [];
+        while (remaining.length > 0) {
+            if (remaining.length <= maxCodePoints) {
+                chunks.push(remaining.join('').trim());
+                break;
+            }
+
+            const remainingSlots = maxChunks - chunks.length;
+            const minimumSplit = Math.max(1, remaining.length - (remainingSlots - 1) * maxCodePoints);
+            let splitAt = maxCodePoints;
+            for (let index = maxCodePoints - 1; index >= minimumSplit; index--) {
+                if (/\s/u.test(remaining[index])) {
+                    splitAt = index;
+                    break;
+                }
+            }
+
+            const chunk = remaining.slice(0, splitAt).join('').trim();
+            remaining = remaining.slice(splitAt);
+            while (remaining.length > 0 && /\s/u.test(remaining[0])) remaining.shift();
+            if (chunk) chunks.push(chunk);
+        }
+
+        return chunks;
+    }
+
+    root.KoalaSyncChatFormat = Object.freeze({ escapeChatHtml, formatChatText, tokenizeChatText, splitChatText });
 })(globalThis);
diff --git a/extension/chat-format.test.mjs b/extension/chat-format.test.mjs
index ece1295..97a70a3 100644
--- a/extension/chat-format.test.mjs
+++ b/extension/chat-format.test.mjs
@@ -19,4 +19,25 @@ describe('chat formatting', () => {
             { type: 'em', text: 'italic' }
         ]);
     });
+
+    it('splits up to 5000 Unicode code points into at most ten ordered chat-v1 messages', () => {
+        const split = globalThis.KoalaSyncChatFormat.splitChatText;
+        expect(split('hello world', 500, 10)).toEqual(['hello world']);
+
+        const emojiChunks = split('😀'.repeat(1001), 500, 10);
+        expect(emojiChunks.map(chunk => [...chunk].length)).toEqual([500, 500, 1]);
+
+        const maximumChunks = split('x'.repeat(5000), 500, 10);
+        expect(maximumChunks).toHaveLength(10);
+        expect(maximumChunks.every(chunk => [...chunk].length === 500)).toBe(true);
+        expect(maximumChunks.join('')).toBe('x'.repeat(5000));
+
+        expect(() => split('x'.repeat(5001), 500, 10)).toThrow(RangeError);
+    });
+
+    it('prefers whitespace boundaries without creating more chunks than the limit allows', () => {
+        const split = globalThis.KoalaSyncChatFormat.splitChatText;
+        const chunks = split(`${'a'.repeat(420)} ${'b'.repeat(179)}`, 500, 10);
+        expect(chunks).toEqual(['a'.repeat(420), 'b'.repeat(179)]);
+    });
 });
diff --git a/extension/chat-overlay-contract.test.mjs b/extension/chat-overlay-contract.test.mjs
index d72cbf9..5989f3b 100644
--- a/extension/chat-overlay-contract.test.mjs
+++ b/extension/chat-overlay-contract.test.mjs
@@ -1,5 +1,6 @@
 import fs from 'node:fs';
 import path from 'node:path';
+import vm from 'node:vm';
 import { fileURLToPath } from 'node:url';
 import { describe, expect, it } from 'vitest';
 
@@ -34,6 +35,15 @@ const chatKeys = [
 ];
 
 describe('chat overlay contract', () => {
+    it('skips SVG and other non-HTML documents before creating the overlay host', () => {
+        const documentGuard = "document.documentElement?.namespaceURI !== 'http://www.w3.org/1999/xhtml'";
+        expect(overlaySource).toContain(documentGuard);
+        expect(overlaySource.indexOf(documentGuard)).toBeLessThan(overlaySource.indexOf("document.createElement('div')"));
+        expect(() => vm.runInNewContext(overlaySource, {
+            document: { documentElement: { namespaceURI: 'http://www.w3.org/2000/svg' } }
+        })).not.toThrow();
+    });
+
     it('isolates the overlay and never renders markup as HTML', () => {
         expect(overlaySource).toContain("attachShadow({ mode: 'open' })");
         expect(overlaySource).not.toMatch(/\.innerHTML\s*=|insertAdjacentHTML|\.outerHTML\s*=/);
@@ -85,6 +95,7 @@ describe('chat overlay contract', () => {
         expect(overlaySource).toContain('margin-right: var(${PAGE_DOCK_WIDTH}) !important');
         expect(overlaySource).toContain('html[${PAGE_DOCK_ATTRIBUTE}] > body');
         expect(overlaySource).toContain('clip-path: inset(0) !important');
+        expect(overlaySource).toContain('contain: layout paint !important');
         expect(overlaySource).toContain('> :not(#koalasync-chat-overlay-host)');
         expect(overlaySource).toContain('const target = document.fullscreenElement || document.documentElement');
         expect(overlaySource).toContain('pageDockTarget = target');
@@ -100,7 +111,9 @@ describe('chat overlay contract', () => {
         expect(overlaySource).toContain("unreadBadge.classList.toggle('visible', unreadCount > 0)");
         expect(backgroundSource).toMatch(/received\.senderId !== peerId[\s\S]*showChatNotification\([\s\S]*senderPeer\.username[\s\S]*received\.senderId/);
         expect(backgroundSource).toContain("chrome.notifications.create(`chat_${Date.now()}`");
-        expect(backgroundSource).toContain("if (settings.chatNotifications === false) return");
+        expect(backgroundSource).toContain('getTabForNotification(targetTabId)');
+        expect(backgroundSource).toContain('getWindowForNotification(tab.windowId)');
+        expect(backgroundSource).toContain('shouldShowChatNotification({ enabled, targetTabId, tab, windowInfo })');
     });
 
     it('renders timestamped room activity and keeps activity notifications opt-in', () => {
@@ -125,12 +138,24 @@ describe('chat overlay contract', () => {
         expect(overlaySource).toContain('launcherIcon.src = LAUNCHER_ICON_DATA_URL');
         expect(manifestSource).not.toContain('web_accessible_resources');
         expect(overlaySource).toContain("const QUICK_REACTIONS = Object.freeze(['❤️', '😂', '😮', '😢', '👏', '🔥'])");
-        expect(overlaySource).toContain("messageRuntime({ type: 'CHAT_SEND', text })");
+        expect(overlaySource).toContain("messageRuntime({ type: 'CHAT_SEND', text: chunk })");
         expect(overlaySource).toContain("chatReactionDisplay !== 'video'");
         expect(overlaySource).toContain('MAX_REACTION_PARTICLES - reactionLayer.childElementCount');
         expect(overlaySource).toContain('reducedMotion.matches');
     });
 
+    it('splits a 5000-codepoint composer value into at most ten acknowledged chat-v1 messages', () => {
+        expect(overlaySource).toContain('const MAX_MESSAGE_CODE_POINTS = 500');
+        expect(overlaySource).toContain('const MAX_CHAT_CHUNKS = 10');
+        expect(overlaySource).toContain('MAX_MESSAGE_CODE_POINTS * MAX_CHAT_CHUNKS');
+        expect(overlaySource).toContain('KoalaSyncChatFormat?.splitChatText(');
+        expect(overlaySource).toMatch(/for \(const chunk of chunks\)[\s\S]*messageRuntime\(\{ type: 'CHAT_SEND', text: chunk \}\)/);
+        expect(overlaySource).toContain("textarea.value = chunks.slice(completedChunks).join('\\n')");
+        expect(backgroundSource).toContain('const echoPromise = chatEchoTracker.waitFor(ciphertext)');
+        expect(backgroundSource).toContain('chatEchoTracker.acknowledge(received.ciphertext)');
+        expect(backgroundSource).toContain("status: acknowledged ? 'ok' : 'unconfirmed'");
+    });
+
     it('excludes test-only modules from production extension artifacts', () => {
         expect(buildSource).toContain("/\\.test\\.[cm]?js$/u.test(item)");
     });
@@ -143,6 +168,9 @@ describe('chat overlay contract', () => {
         expect(overlaySource).toContain('setTimeout(() => finish(null), timeoutMs)');
         expect(backgroundSource).toContain('chatReceiveQueue = chatReceiveQueue.catch(() => {}).then');
         expect(backgroundSource).toContain("status: 'rate_limited'");
+        expect(overlaySource).toContain('function setLocalStorage(values)');
+        expect(overlaySource).toMatch(/chrome\.storage\.local\.get\([\s\S]*data => \{\s*if \(destroyed\) return;/);
+        expect(overlaySource).toContain("if (destroyed || area !== 'local') return");
     });
 
     it('keeps chat hidden by default without discarding the room chat key', () => {
diff --git a/extension/chat-overlay.js b/extension/chat-overlay.js
index 3e03c13..22a4273 100644
--- a/extension/chat-overlay.js
+++ b/extension/chat-overlay.js
@@ -1,4 +1,6 @@
 (function initKoalaSyncChatOverlay() {
+    if (document.documentElement?.namespaceURI !== 'http://www.w3.org/1999/xhtml') return;
+
     if (window.koalaSyncChatOverlay?.refresh) {
         window.koalaSyncChatOverlay.refresh();
         return;
@@ -11,6 +13,9 @@
     const DEFAULT_HEIGHT = 520;
     const LAUNCHER_SIZE = 48;
     const EDGE_INSET = 8;
+    const MAX_MESSAGE_CODE_POINTS = 500;
+    const MAX_CHAT_CHUNKS = 10;
+    const MAX_COMPOSER_CODE_POINTS = MAX_MESSAGE_CODE_POINTS * MAX_CHAT_CHUNKS;
     const PAGE_DOCK_ATTRIBUTE = 'data-koalasync-chat-dock';
     const PAGE_DOCK_WIDTH = '--koalasync-chat-dock-width';
     const QUICK_REACTIONS = Object.freeze(['❤️', '😂', '😮', '😢', '👏', '🔥']);
@@ -268,7 +273,7 @@
     textarea.id = 'chat-composer-input';
     textarea.setAttribute('aria-describedby', 'chat-composer-count chat-composer-status');
     const composerRow = element('div', 'composer-row');
-    const count = element('span', 'count', '0/500');
+    const count = element('span', 'count', `0/${MAX_COMPOSER_CODE_POINTS}`);
     count.id = 'chat-composer-count';
     const sendButton = element('button', 'send');
     sendButton.type = 'submit';
@@ -306,6 +311,7 @@
             min-height: 100vh !important;
             overflow-x: clip !important;
             clip-path: inset(0) !important;
+            contain: layout paint !important;
         }
         [${PAGE_DOCK_ATTRIBUTE}]:not(html) > :not(#koalasync-chat-overlay-host) {
             box-sizing: border-box !important;
@@ -313,6 +319,7 @@
             max-width: calc(100% - var(${PAGE_DOCK_WIDTH})) !important;
             overflow-x: clip !important;
             clip-path: inset(0) !important;
+            contain: layout paint !important;
         }
         [${PAGE_DOCK_ATTRIBUTE}="left"]:not(html) > :not(#koalasync-chat-overlay-host) {
             margin-left: var(${PAGE_DOCK_WIDTH}) !important;
@@ -346,6 +353,16 @@
         });
     }
 
+    function setLocalStorage(values) {
+        if (destroyed) return;
+        try {
+            const result = chrome.storage.local.set(values);
+            if (result?.catch) result.catch(() => {});
+        } catch (_) {
+            // Extension context was invalidated while the page remained open.
+        }
+    }
+
     function strings() {
         return context?.strings || {};
     }
@@ -477,11 +494,12 @@
         if (saveTimer) clearTimeout(saveTimer);
         saveTimer = setTimeout(() => {
             saveTimer = null;
-            chrome.storage.local.set({ [storageKey]: layout }).catch(() => {});
+            setLocalStorage({ [storageKey]: layout });
         }, 150);
     }
 
     function applyLayout() {
+        if (destroyed) return;
         applyingLayout = true;
         const size = preferredSize();
         launcher.classList.toggle('docked-left', layout.mode === 'left');
@@ -539,7 +557,7 @@
         layout.mode = mode;
         applyLayout();
         saveLayout();
-        if (persistPreference) chrome.storage.local.set({ chatPosition: mode }).catch(() => {});
+        if (persistPreference) setLocalStorage({ chatPosition: mode });
     }
 
     function setSize(size, persistPreference = true) {
@@ -555,7 +573,7 @@
         if (layout.mode === 'detached') clampDetached();
         applyLayout();
         saveLayout();
-        if (persistPreference) chrome.storage.local.set({ chatSize }).catch(() => {});
+        if (persistPreference) setLocalStorage({ chatSize });
     }
 
     function setOpened(next) {
@@ -699,12 +717,19 @@
         }
     }
 
+    function updateComposerState() {
+        const length = [...textarea.value].length;
+        count.textContent = `${length}/${MAX_COMPOSER_CODE_POINTS}`;
+        count.style.color = length > MAX_COMPOSER_CODE_POINTS ? 'var(--danger)' : '';
+        status.textContent = length > MAX_COMPOSER_CODE_POINTS ? (strings().tooLong || '') : '';
+        return length;
+    }
+
     function resetComposer() {
         sendGeneration++;
         sending = false;
         textarea.value = '';
-        count.textContent = '0/500';
-        count.style.color = '';
+        updateComposerState();
         status.textContent = '';
         sendButton.disabled = false;
         for (const button of reactionButtons) button.disabled = false;
@@ -758,12 +783,7 @@
     detachedButton.addEventListener('click', () => setMode('detached'));
     rightButton.addEventListener('click', () => setMode('right'));
 
-    textarea.addEventListener('input', () => {
-        const length = [...textarea.value].length;
-        count.textContent = `${length}/500`;
-        count.style.color = length > 500 ? 'var(--danger)' : '';
-        status.textContent = length > 500 ? (strings().tooLong || '') : '';
-    });
+    textarea.addEventListener('input', updateComposerState);
     const stopPageKeyboardShortcut = event => {
         const path = typeof event.composedPath === 'function' ? event.composedPath() : [];
         if (!path.includes(textarea) && !path.includes(composer)) return;
@@ -780,26 +800,48 @@
         if (sending || !context?.enabled) return;
         text = String(text || '').trim();
         if (!text) return;
-        if ([...text].length > 500) {
+        if ([...text].length > MAX_COMPOSER_CODE_POINTS) {
             status.textContent = strings().tooLong || '';
             return;
         }
+        let chunks;
+        try {
+            chunks = globalThis.KoalaSyncChatFormat?.splitChatText(
+                text,
+                MAX_MESSAGE_CODE_POINTS,
+                MAX_CHAT_CHUNKS
+            );
+        } catch (_) {
+            status.textContent = strings().tooLong || '';
+            return;
+        }
+        if (!Array.isArray(chunks) || chunks.length === 0) return;
         const generation = ++sendGeneration;
         sending = true;
         sendButton.disabled = true;
         for (const button of reactionButtons) button.disabled = true;
         status.textContent = '';
-        const response = await messageRuntime({ type: 'CHAT_SEND', text });
-        if (destroyed || generation !== sendGeneration) return;
+        let completedChunks = 0;
+        let response = null;
+        for (const chunk of chunks) {
+            response = await messageRuntime({ type: 'CHAT_SEND', text: chunk });
+            if (destroyed || generation !== sendGeneration) return;
+            if (response?.status !== 'ok') break;
+            completedChunks++;
+        }
         sending = false;
         sendButton.disabled = false;
         for (const button of reactionButtons) button.disabled = false;
-        if (response?.status === 'ok') {
+        if (completedChunks === chunks.length) {
             if (clearComposerValue && textarea.value.trim() === text) {
                 textarea.value = '';
-                count.textContent = '0/500';
+                updateComposerState();
             }
         } else {
+            if (clearComposerValue && textarea.value.trim() === text) {
+                textarea.value = chunks.slice(completedChunks).join('\n');
+                updateComposerState();
+            }
             status.textContent = response?.status === 'too_long' ? (strings().tooLong || '') : (strings().sendFailed || '');
         }
     }
@@ -841,7 +883,7 @@
         layout.customHeight = rect.height;
         if (chatSize !== 'custom') {
             chatSize = 'custom';
-            chrome.storage.local.set({ chatSize }).catch(() => {});
+            setLocalStorage({ chatSize });
         }
         clampDetached();
         saveLayout();
@@ -868,7 +910,7 @@
     }
 
     function handleStorage(changes, area) {
-        if (area !== 'local') return;
+        if (destroyed || area !== 'local') return;
         if (changes.themeMode) themeMode = changes.themeMode.newValue || 'system';
         if (changes.themePalette) themePalette = changes.themePalette.newValue || 'eucalyptus';
         if (changes.themeMode || changes.themePalette) applyTheme();
@@ -896,7 +938,7 @@
             resetComposer();
             refresh();
         }
-        if (message?.type === 'CHAT_DESTROY') destroy();
+        if (message?.type === 'CHAT_DESTROY' || message?.type === 'TARGET_DEACTIVATE') destroy();
     }
 
     function destroy() {
@@ -914,8 +956,8 @@
         document.removeEventListener('fullscreenchange', moveIntoFullscreen);
         window.removeEventListener('resize', handleResize);
         systemTheme.removeEventListener('change', handleSystemTheme);
-        chrome.storage.onChanged.removeListener(handleStorage);
-        chrome.runtime.onMessage.removeListener(handleRuntime);
+        try { chrome.storage.onChanged.removeListener(handleStorage); } catch (_) { /* invalidated context */ }
+        try { chrome.runtime.onMessage.removeListener(handleRuntime); } catch (_) { /* invalidated context */ }
         host.remove();
         window.koalaSyncChatOverlay = null;
     }
@@ -926,6 +968,7 @@
     chrome.storage.onChanged.addListener(handleStorage);
     chrome.runtime.onMessage.addListener(handleRuntime);
     chrome.storage.local.get([storageKey, 'themeMode', 'themePalette', 'chatPosition', 'chatSize', 'chatStartMode', 'chatReactionDisplay'], data => {
+        if (destroyed) return;
         const storedLayout = data[storageKey];
         if (storedLayout && typeof storedLayout === 'object') {
             layout = { ...layout, ...storedLayout };
diff --git a/extension/chat-session.js b/extension/chat-session.js
index 1458904..fac18ac 100644
--- a/extension/chat-session.js
+++ b/extension/chat-session.js
@@ -1,6 +1,7 @@
 export const MAX_ROOM_ID_LENGTH = 64;
-export const CHAT_SEND_LIMIT = 9;
+export const CHAT_SEND_LIMIT = 10;
 export const CHAT_SEND_WINDOW_MS = 10000;
+export const CHAT_ECHO_TIMEOUT_MS = 4000;
 
 export function normalizeRoomId(value) {
     if (typeof value !== 'string') return '';
@@ -33,6 +34,58 @@ export function createChatSendLimiter({
     };
 }
 
+export function createChatEchoTracker({
+    timeoutMs = CHAT_ECHO_TIMEOUT_MS,
+    setTimer = globalThis.setTimeout,
+    clearTimer = globalThis.clearTimeout
+} = {}) {
+    const pending = new Map();
+
+    function settle(ciphertext, acknowledged) {
+        const entry = pending.get(ciphertext);
+        if (!entry) return false;
+        pending.delete(ciphertext);
+        clearTimer(entry.timer);
+        entry.resolve(acknowledged);
+        return true;
+    }
+
+    return {
+        waitFor(ciphertext) {
+            if (typeof ciphertext !== 'string' || !ciphertext) return Promise.resolve(false);
+            settle(ciphertext, false);
+            return new Promise(resolve => {
+                const timer = setTimer(() => {
+                    pending.delete(ciphertext);
+                    resolve(false);
+                }, timeoutMs);
+                pending.set(ciphertext, { resolve, timer });
+            });
+        },
+        acknowledge(ciphertext) {
+            return settle(ciphertext, true);
+        },
+        cancel(ciphertext) {
+            return settle(ciphertext, false);
+        },
+        reset() {
+            for (const ciphertext of [...pending.keys()]) settle(ciphertext, false);
+        }
+    };
+}
+
+export function shouldShowChatNotification({ enabled, targetTabId, tab, windowInfo }) {
+    if (!enabled) return false;
+    const normalizedTargetTabId = Number(targetTabId);
+    const targetIsFocused = Number.isInteger(normalizedTargetTabId)
+        && tab?.id === normalizedTargetTabId
+        && tab.active === true
+        && Number.isInteger(tab.windowId)
+        && windowInfo?.id === tab.windowId
+        && windowInfo.focused === true;
+    return !targetIsFocused;
+}
+
 export function createLatestTaskQueue() {
     let generation = 0;
     let tail = Promise.resolve();
diff --git a/extension/chat-session.test.mjs b/extension/chat-session.test.mjs
index 3c5d5b2..e496937 100644
--- a/extension/chat-session.test.mjs
+++ b/extension/chat-session.test.mjs
@@ -1,10 +1,14 @@
 import { describe, expect, it } from 'vitest';
+import { CHAT_MESSAGE_RATE_LIMIT } from '../server/rate-limiter.js';
 import {
+    CHAT_ECHO_TIMEOUT_MS,
     CHAT_SEND_LIMIT,
+    createChatEchoTracker,
     createChatSendLimiter,
     createLatestTaskQueue,
     MAX_ROOM_ID_LENGTH,
-    normalizeRoomId
+    normalizeRoomId,
+    shouldShowChatNotification
 } from './chat-session.js';
 
 describe('chat session boundaries', () => {
@@ -14,7 +18,8 @@ describe('chat session boundaries', () => {
         expect(normalizeRoomId(null)).toBe('');
     });
 
-    it('keeps client chat bursts below the relay disconnect threshold', () => {
+    it('allows ten-message client bursts without exceeding the relay threshold', () => {
+        expect(CHAT_SEND_LIMIT).toBe(CHAT_MESSAGE_RATE_LIMIT);
         let current = 1000;
         const limiter = createChatSendLimiter({ now: () => current });
         for (let index = 0; index < CHAT_SEND_LIMIT; index++) {
@@ -27,6 +32,49 @@ describe('chat session boundaries', () => {
         expect(limiter.take()).toEqual({ allowed: true, retryAfterMs: 0 });
     });
 
+    it('waits for the matching relay echo and clears pending sends on reset or timeout', async () => {
+        const timers = new Map();
+        let nextTimerId = 1;
+        const tracker = createChatEchoTracker({
+            setTimer(callback, timeoutMs) {
+                const id = nextTimerId++;
+                timers.set(id, { callback, timeoutMs });
+                return id;
+            },
+            clearTimer(id) {
+                timers.delete(id);
+            }
+        });
+
+        const acknowledged = tracker.waitFor('ciphertext-1');
+        expect(tracker.acknowledge('ciphertext-1')).toBe(true);
+        await expect(acknowledged).resolves.toBe(true);
+
+        const reset = tracker.waitFor('ciphertext-2');
+        tracker.reset();
+        await expect(reset).resolves.toBe(false);
+
+        const timedOut = tracker.waitFor('ciphertext-3');
+        const timeout = [...timers.values()][0];
+        expect(timeout.timeoutMs).toBe(CHAT_ECHO_TIMEOUT_MS);
+        timeout.callback();
+        await expect(timedOut).resolves.toBe(false);
+    });
+
+    it('suppresses chat notifications only while the target tab and its window are focused', () => {
+        const focused = {
+            enabled: true,
+            targetTabId: 7,
+            tab: { id: 7, active: true, windowId: 3 },
+            windowInfo: { id: 3, focused: true }
+        };
+        expect(shouldShowChatNotification(focused)).toBe(false);
+        expect(shouldShowChatNotification({ ...focused, windowInfo: { id: 3, focused: false } })).toBe(true);
+        expect(shouldShowChatNotification({ ...focused, tab: { id: 7, active: false, windowId: 3 } })).toBe(true);
+        expect(shouldShowChatNotification({ ...focused, targetTabId: 8 })).toBe(true);
+        expect(shouldShowChatNotification({ ...focused, enabled: false })).toBe(false);
+    });
+
     it('serializes join work and prevents an older request from winning storage races', async () => {
         const queue = createLatestTaskQueue();
         let releaseFirst;
diff --git a/extension/content.js b/extension/content.js
index aa05517..fbe7147 100644
--- a/extension/content.js
+++ b/extension/content.js
@@ -12,7 +12,34 @@
     } catch (_e) {

         // Context invalidated, proceed with re-injection

     }

-    window.koalaSyncInjected = true;

+    window.koalaSyncInjected = true;
+    let destroyed = false;
+    const lifecycleTimeouts = new Set();
+    const seekPollTimers = new Set();
+    const attachedVideos = new Set();
+
+    function scheduleLifecycleTimeout(callback, delay) {
+        const timer = setTimeout(() => {
+            lifecycleTimeouts.delete(timer);
+            if (!destroyed) callback();
+        }, delay);
+        lifecycleTimeouts.add(timer);
+        return timer;
+    }
+
+    function runtimeMessage(message, callback) {
+        if (destroyed) return Promise.resolve(undefined);
+        try {
+            if (!chrome.runtime?.id) {
+                destroyContentScript();
+                return Promise.resolve(undefined);
+            }
+            return chrome.runtime.sendMessage(message, callback) || Promise.resolve(undefined);
+        } catch (_e) {
+            destroyContentScript();
+            return Promise.resolve(undefined);
+        }
+    }
 

     // --- SHARED_EVENTS_INJECT_START ---

     // This block is automatically updated by /scripts/build-extension.cjs
@@ -62,15 +89,16 @@
     // (background.js installPageApiSeekBridge). The isolated content world
     // can't read the page's media player directly.
     let disneyPageApiTime = null;
+    function handlePageApiTime(event) {
+        if (destroyed || event.source !== window) return;
+        const data = event.data;
+        if (data && data.__koalaPlayerTime === 1 && data.provider === 'disney'
+            && Number.isFinite(data.position) && Number.isFinite(data.duration) && data.duration > 0) {
+            disneyPageApiTime = { position: data.position, duration: data.duration, at: Date.now() };
+        }
+    }
     if (typeof window !== 'undefined' && typeof window.addEventListener === 'function') {
-        window.addEventListener('message', (event) => {
-            if (event.source !== window) return;
-            const data = event.data;
-            if (data && data.__koalaPlayerTime === 1 && data.provider === 'disney'
-                && Number.isFinite(data.position) && Number.isFinite(data.duration) && data.duration > 0) {
-                disneyPageApiTime = { position: data.position, duration: data.duration, at: Date.now() };
-            }
-        });
+        window.addEventListener('message', handlePageApiTime);
     }
 
     function hostMatchesUrl(host, url) {
@@ -210,17 +238,20 @@
     let _audioProcessingAllowed = true;

 

     // Cache the autoSyncNextEpisode setting (local-only; never read from sync)

-    chrome.storage.local.get(['autoSyncNextEpisode', 'audioSettings'], (data) => {

+    chrome.storage.local.get(['autoSyncNextEpisode', 'audioSettings'], (data) => {
+        if (destroyed) return;
         _autoSyncEnabled = data.autoSyncNextEpisode !== false;

         _audioSettings = mergeAudioSettings(data.audioSettings);

         const video = findVideo();

         if (video && _audioProcessingAllowed) applyAudioSettings(video, _audioSettings);

     });

-    chrome.storage.onChanged.addListener((changes, area) => {

-        if (area === 'local' && changes.autoSyncNextEpisode) {

-            _autoSyncEnabled = changes.autoSyncNextEpisode.newValue !== false;

-        }

-    });

+    function handleStorageChanged(changes, area) {
+        if (destroyed) return;
+        if (area === 'local' && changes.autoSyncNextEpisode) {
+            _autoSyncEnabled = changes.autoSyncNextEpisode.newValue !== false;
+        }
+    }
+    chrome.storage.onChanged.addListener(handleStorageChanged);
 

     // --- Host Control Mode (guest-side) ---

     // When a room is in 'host-only' mode and we're a guest, a deliberate local

@@ -234,8 +265,9 @@
     let hcmSnapBackCooldownUntil = 0;  // suppress re-trigger right after a snap-back

     let hcmDeferredSnapPending = false; // a buffer-aware snap-back is waiting for readiness

     let hcmLastUserGestureAt = 0;      // for deliberate-vs-involuntary classification

-    let hcmBufferingUntil = 0;         // set on 'waiting' — buffering grace window

-    let hcmDialogTimer = null;         // 8s auto-stay timer — cleared on dialog replace (H-4)

+    let hcmBufferingUntil = 0;         // set on 'waiting' — buffering grace window
+    let hcmDialogTimer = null;         // 8s auto-stay timer — cleared on dialog replace (H-4)
+    let hcmBadgeDomReadyHandler = null;
     // Localized strings for the in-page dialog/badge (content has no i18n loader;

     // background resolves them via GET_HCM_STRINGS on init). English fallbacks here.

     const hcmStrings = {

@@ -320,9 +352,9 @@
     function hcmRequestHostSyncWithRetry() {

         let attempts = 0;

         const tryOnce = () => {

-            chrome.runtime.sendMessage({ type: 'REQUEST_HOST_SYNC' }, (res) => {

+            runtimeMessage({ type: 'REQUEST_HOST_SYNC' }, (res) => {
                 if (chrome.runtime.lastError || !res || !res.target) {

-                    if (++attempts < 5) setTimeout(tryOnce, 250);

+                    if (++attempts < 5) scheduleLifecycleTimeout(tryOnce, 250);
                     else reportLog('Host-only: resync requested but host state unavailable', 'warn');

                     return;

                 }

@@ -355,7 +387,7 @@
                 hcmRequestHostSyncWithRetry(); // fresh host position + snap once

                 return;

             }

-            setTimeout(poll, 300);

+            scheduleLifecycleTimeout(poll, 300);
         };

         poll();

     }

@@ -457,7 +489,7 @@
         // Notify background so it can relay our desynced state to the host via

         // heartbeats — the host's UI then knows we're not following commands

         // instead of appearing silently un-ACK'd.

-        chrome.runtime.sendMessage({ type: 'HCM_DESYNC_STATE', desynced: true }).catch(() => {});

+        runtimeMessage({ type: 'HCM_DESYNC_STATE', desynced: true }).catch(() => {});
         hcmShowBadge();

     }

 

@@ -466,7 +498,7 @@
         hcmDesynced = false;

         hcmRemoveBadge();

         if (wasDesynced) {

-            chrome.runtime.sendMessage({ type: 'HCM_DESYNC_STATE', desynced: false }).catch(() => {});

+            runtimeMessage({ type: 'HCM_DESYNC_STATE', desynced: false }).catch(() => {});
         }

         // Resync to the host's current position (retries if host state not yet known).

         hcmRequestHostSyncWithRetry();

@@ -480,14 +512,16 @@
             // otherwise the desynced user silently never sees the badge (L-4).

             if (!hcmBadgePending) {

                 hcmBadgePending = true;

-                const retry = () => {

-                    hcmBadgePending = false;

-                    if (hcmDesynced && !hcmBadgeHost) hcmShowBadge();

-                };

-                if (document.readyState === 'loading') {

-                    document.addEventListener('DOMContentLoaded', retry, { once: true });

+                const retry = () => {
+                    hcmBadgeDomReadyHandler = null;
+                    hcmBadgePending = false;
+                    if (hcmDesynced && !hcmBadgeHost) hcmShowBadge();
+                };
+                if (document.readyState === 'loading') {
+                    hcmBadgeDomReadyHandler = retry;
+                    document.addEventListener('DOMContentLoaded', retry, { once: true });
                 } else {

-                    setTimeout(retry, 50);

+                    scheduleLifecycleTimeout(retry, 50);
                 }

             }

             return;

@@ -518,12 +552,12 @@
         // desynced in heartbeats (otherwise the host's UI keeps showing the

         // stale Solo badge until the next state change).

         if (wasDesynced) {

-            chrome.runtime.sendMessage({ type: 'HCM_DESYNC_STATE', desynced: false }).catch(() => {});

+            runtimeMessage({ type: 'HCM_DESYNC_STATE', desynced: false }).catch(() => {});
         }

     }

 

     function reportLog(message, level = 'info') {

-        chrome.runtime.sendMessage({ type: 'LOG', message, level }).catch(() => {});

+        runtimeMessage({ type: 'LOG', message, level }).catch(() => {});
     }

 

     // --- Helper: find the best video element on the page ---

@@ -786,7 +820,7 @@
         // Do NOT pause here. We notify background.js first.

         // Background checks the setting; if enabled it creates a lobby

         // and sends back PAUSE_FOR_LOBBY so we only freeze if the feature is on.

-        chrome.runtime.sendMessage({

+        runtimeMessage({
             type: 'EPISODE_CHANGED',

             payload: { newTitle }

         }).catch(() => {});

@@ -810,7 +844,7 @@
                 video.pause();

             }

             stopLobbyPoll();

-            chrome.runtime.sendMessage({

+            runtimeMessage({
                 type: 'EPISODE_READY_LOCAL',

                 payload: { title: currentTitle }

             }).catch(() => {});

@@ -923,36 +957,52 @@
     }

 

     // --- Helper: Wait until video is ready for playback (buffered & seeked) ---

-    function pollSeekReady(targetTime, timeoutMs = 8000) {

-        return new Promise((resolve) => {

-            const interval = 150;

-            let elapsed = 0;

-            const timer = setInterval(() => {

-                const video = findVideo(); // Re-query DOM on every iteration

-                if (!video) {

-                    clearInterval(timer);

-                    resolve(false);

-                    return;

+    function pollSeekReady(targetTime, timeoutMs = 8000) {
+        return new Promise((resolve) => {
+            const interval = 150;
+            let elapsed = 0;
+            const timer = setInterval(() => {
+                if (destroyed) {
+                    clearInterval(timer);
+                    seekPollTimers.delete(timer);
+                    resolve(false);
+                    return;
+                }
+                const video = findVideo(); // Re-query DOM on every iteration
+                if (!video) {
+                    clearInterval(timer);
+                    seekPollTimers.delete(timer);
+                    resolve(false);
+                    return;
                 }

 

                 elapsed += interval;

                 const current = getSyncCurrentTime(video);
                 const timeDiff = current !== null ? Math.abs(current - targetTime) : Infinity;
                 const ready = video.readyState >= 3 && timeDiff < 2.0;
-                if (ready) {

-                    clearInterval(timer);

-                    resolve(true);

-                } else if (elapsed >= timeoutMs) {

-                    clearInterval(timer);

-                    resolve(false);

-                }

-            }, interval);

-        });

-    }

+                if (ready) {
+                    clearInterval(timer);
+                    seekPollTimers.delete(timer);
+                    resolve(true);
+                } else if (elapsed >= timeoutMs) {
+                    clearInterval(timer);
+                    seekPollTimers.delete(timer);
+                    resolve(false);
+                }
+            }, interval);
+            seekPollTimers.add(timer);
+        });
+    }
 

     // Listen for commands from background.js

-    chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {

+    function handleRuntimeMessage(message, sender, sendResponse) {
         if (!message) return;
+        if (message.type === 'TARGET_DEACTIVATE') {
+            destroyContentScript();
+            sendResponse({ ok: true });
+            return true;
+        }
+        if (destroyed) return;
         if (message.action === 'get_current_time') {
             const video = findVideo();
             sendResponse({ currentTime: video ? getSyncCurrentTime(video) : null });
@@ -1019,7 +1069,7 @@
                 const soloIgnored = [EVENTS.PLAY, EVENTS.PAUSE, EVENTS.SEEK, EVENTS.FORCE_SYNC_PREPARE, EVENTS.FORCE_SYNC_EXECUTE];

                 if (soloIgnored.includes(action)) {

                     if (action === EVENTS.FORCE_SYNC_PREPARE) {

-                        chrome.runtime.sendMessage({ type: 'FORCE_SYNC_ACK' }).catch(() => {});

+                        runtimeMessage({ type: 'FORCE_SYNC_ACK' }).catch(() => {});
                     }

                     return;

                 }

@@ -1037,7 +1087,7 @@
                 if (isDifferentEpisode(senderTitle, myTitle)) {

                     reportLog(`Episode mismatch: sender="${senderTitle || '?'}" vs mine="${myTitle || '?'}" — skipping ${action}. Disable "Auto-Sync next Episode" in settings if this causes issues.`, 'warn');

                     if (action !== EVENTS.FORCE_SYNC_PREPARE && action !== EVENTS.FORCE_SYNC_EXECUTE) {

-                        chrome.runtime.sendMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId }).catch(() => {});

+                        runtimeMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId }).catch(() => {});
                     }

                     return;

                 }

@@ -1045,15 +1095,15 @@
             

             if (action === EVENTS.PLAY) {

                 tryMediaAction(EVENTS.PLAY);

-                chrome.runtime.sendMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });

+                runtimeMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });
                 actionCompleted = true;

             } else if (action === EVENTS.PAUSE) {

                 tryMediaAction(EVENTS.PAUSE);

-                chrome.runtime.sendMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });

+                runtimeMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });
                 actionCompleted = true;

             } else if (action === EVENTS.SEEK) {

                 tryMediaAction(EVENTS.SEEK, payload);

-                chrome.runtime.sendMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });

+                runtimeMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });
                 actionCompleted = true;

             } else if (action === EVENTS.FORCE_SYNC_PREPARE) {

                 if (!payload || payload.targetTime === undefined) return;

@@ -1071,7 +1121,7 @@
                         reportLog(`Force Sync Seek Error: ${e.message}`, 'error');

                     }

                     pollSeekReady(payload.targetTime).then((ready) => {

-                        chrome.runtime.sendMessage({ type: 'FORCE_SYNC_ACK' }).catch(() => {});

+                        runtimeMessage({ type: 'FORCE_SYNC_ACK' }).catch(() => {});
                         if (ready) {

                             scheduleProactiveHeartbeat();

                         } else {

@@ -1082,7 +1132,7 @@
             } else if (action === EVENTS.FORCE_SYNC_EXECUTE) {

                 stopLobbyPoll();

                 tryMediaAction(EVENTS.PLAY);

-                chrome.runtime.sendMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });

+                runtimeMessage({ type: 'CMD_ACK', actionTimestamp: message.actionTimestamp, commandSenderId: message.commandSenderId });
                 actionCompleted = true;

             }

 

@@ -1265,14 +1315,16 @@
                 });

             }

         }

-    });

+    }
+    chrome.runtime.onMessage.addListener(handleRuntimeMessage);
 

     // Detect native events

     // Build the relay payload from the *current* media state and send it to

     // background.js. Re-reads the video each call so deferred (coalesced) emits

     // carry an up-to-date position. Safe with no/invalid video — it no-ops.

-    function sendContentEvent(action) {

-        const video = findVideo();

+    function sendContentEvent(action) {
+        if (destroyed) return;
+        const video = findVideo();
         if (!video) return;

 

         const current = getSyncCurrentTime(video);
@@ -1280,7 +1332,7 @@
 

         const mediaTitle = (navigator.mediaSession && navigator.mediaSession.metadata) ? navigator.mediaSession.metadata.title : null;

 

-        chrome.runtime.sendMessage({

+        runtimeMessage({
             type: 'CONTENT_EVENT',

             action,

             payload: {

@@ -1308,8 +1360,9 @@
         sendContentEvent(finalAction);

     }

 

-    function reportEvent(action) {

-        if (seekDebounceTimer && (action === EVENTS.PLAY || action === EVENTS.PAUSE)) {

+    function reportEvent(action) {
+        if (destroyed) return;
+        if (seekDebounceTimer && (action === EVENTS.PLAY || action === EVENTS.PAUSE)) {
             clearTimeout(seekDebounceTimer);

             seekDebounceTimer = null;

             const v = findVideo();

@@ -1373,42 +1426,64 @@
     // We suppress only SEEK for a short grace period after tab re-focus.

     // Play/Pause are NOT suppressed — the user may legitimately want to

     // pause immediately after switching back.

-    let pageVisible = !document.hidden;

+    let pageVisible = !document.hidden;
+    let pageSuspended = false;
     let visibilityGraceUntil = 0;

     const VISIBILITY_GRACE_MS = 300;

 

-    document.addEventListener('visibilitychange', () => {

-        if (document.hidden) {

-            pageVisible = false;

-        } else if (!pageVisible) {

+    function handleVisibilityChange() {
+        if (destroyed) return;
+        try {
+            if (!chrome.runtime?.id) {
+                destroyContentScript();
+                return;
+            }
+        } catch (_e) {
+            destroyContentScript();
+            return;
+        }
+        if (document.hidden) {
+            pageVisible = false;
+        } else if (!pageVisible) {
             pageVisible = true;

             visibilityGraceUntil = Date.now() + VISIBILITY_GRACE_MS;

-            reportLog(`Tab re-focused — suppressing seeks for ${VISIBILITY_GRACE_MS / 1000}s to prevent ghost relay`, 'warn');

-        }

-    });

-

-    // Reset on page hide/show (bfcache, tab discard)

-    window.addEventListener('pagehide', () => {

-        pageVisible = false;

-        closeAudioContext();

-        if (keepAlivePort) { try { keepAlivePort.disconnect(); } catch (_e) { /* ignore */ } keepAlivePort = null; }

+            reportLog(`Tab re-focused — suppressing seeks for ${VISIBILITY_GRACE_MS / 1000}s to prevent ghost relay`, 'warn');
+        }
+    }
+
+    // Reset on page hide/show (bfcache, tab discard)
+    function handlePageHide() {
+        if (destroyed) return;
+        pageSuspended = true;
+        pageVisible = false;
+        closeAudioContext();
+        if (keepAlivePort) { try { keepAlivePort.disconnect(); } catch (_e) { /* ignore */ } keepAlivePort = null; }
         if (lobbyPollTimer) { clearInterval(lobbyPollTimer); lobbyPollTimer = null; }

         if (heartbeatTimeout) { clearTimeout(heartbeatTimeout); heartbeatTimeout = null; }

         if (proactiveHeartbeatTimeout) { clearTimeout(proactiveHeartbeatTimeout); proactiveHeartbeatTimeout = null; }

         // Drop any pending coalesced play/pause: we are tearing down and will

         // disconnect — peers learn we are gone via PEER_STATUS 'left'. This also

         // intentionally suppresses the teardown play/pause burst at the source.

-        if (playPauseCoalesceTimer) { clearTimeout(playPauseCoalesceTimer); playPauseCoalesceTimer = null; pendingPlayPauseAction = null; }

-        observer.disconnect();

-    });

-    window.addEventListener('pageshow', (event) => {

-        // event.persisted is true ONLY when restored from bfcache, not on initial load

-        if (event.persisted && !pageVisible) {

-            pageVisible = true;

-            visibilityGraceUntil = Date.now() + VISIBILITY_GRACE_MS;

-            reportLog(`Page restored from cache — suppressing seeks for ${VISIBILITY_GRACE_MS / 1000}s`, 'warn');

-        }

-    });

+        if (playPauseCoalesceTimer) { clearTimeout(playPauseCoalesceTimer); playPauseCoalesceTimer = null; pendingPlayPauseAction = null; }
+        observer.disconnect();
+    }
+    function handlePageShow(event) {
+        if (destroyed) return;
+        // event.persisted is true ONLY when restored from bfcache, not on initial load
+        if (!event.persisted) return;
+        pageSuspended = false;
+        pageVisible = !document.hidden;
+        if (pageVisible) visibilityGraceUntil = Date.now() + VISIBILITY_GRACE_MS;
+        observer.observe(document.documentElement, { childList: true, subtree: true });
+        setupListeners();
+        connectKeepAlivePort();
+        schedulePeriodicHeartbeat();
+        scheduleProactiveHeartbeat();
+        reportLog(`Page restored from cache — suppressing seeks for ${VISIBILITY_GRACE_MS / 1000}s`, 'warn');
+    }
+    document.addEventListener('visibilitychange', handleVisibilityChange);
+    window.addEventListener('pagehide', handlePageHide);
+    window.addEventListener('pageshow', handlePageShow);
 

     const handlePlay = () => reportEvent(EVENTS.PLAY);

     const handlePause = () => reportEvent(EVENTS.PAUSE);

@@ -1475,8 +1550,9 @@
     };

 

     function setupListeners() {
-        const video = findVideo();

-        if (video) {

+        if (destroyed) return;
+        const video = findVideo();
+        if (video) {
             if (currentAudioVideo && currentAudioVideo !== video) {

                 bypassCurrentAudioProcessing();

             }

@@ -1492,9 +1568,10 @@
             video.addEventListener('play', handlePlay);

             video.addEventListener('pause', handlePause);

             video.addEventListener('seeked', handleSeeked);

-            video.addEventListener('loadeddata', handleLoadedData);

-            video.addEventListener('waiting', handleWaiting);

-            video.dataset.koalaAttached = 'true';

+            video.addEventListener('loadeddata', handleLoadedData);
+            video.addEventListener('waiting', handleWaiting);
+            attachedVideos.add(video);
+            video.dataset.koalaAttached = 'true';
             lastVideoSrc = video.currentSrc || video.src || null;

 

             if (!lastKnownMediaTitle) {

@@ -1509,8 +1586,9 @@
     let lastMutate = 0;

     let observerTimeout = null;

 

-    function checkVideo() {

-        lastMutate = Date.now();

+    function checkVideo() {
+        if (destroyed) return;
+        lastMutate = Date.now();
         const video = findVideo();

 

         if (!video && lastVideoSrc !== undefined) {

@@ -1532,8 +1610,9 @@
         }

     }

 

-    const observer = new MutationObserver(() => {

-        const now = Date.now();

+    const observer = new MutationObserver(() => {
+        if (destroyed) return;
+        const now = Date.now();
         if (now - lastMutate >= 1000) {

             checkVideo();

         } else {

@@ -1552,12 +1631,13 @@
     let proactiveHeartbeatTimeout = null;

     let heartbeatErrorCount = 0;

 

-    function sendHeartbeat() {

-        const video = findVideo();

+    function sendHeartbeat() {
+        if (destroyed) return;
+        const video = findVideo();
         if (!video) return;

 

         const mediaTitle = (navigator.mediaSession && navigator.mediaSession.metadata) ? navigator.mediaSession.metadata.title : null;

-        chrome.runtime.sendMessage({

+        runtimeMessage({
             type: 'HEARTBEAT',

             payload: {

                 playbackState: video.paused ? 'paused' : 'playing',

@@ -1579,18 +1659,22 @@
         });

     }

 

-    function schedulePeriodicHeartbeat() {

-        if (heartbeatTimeout) clearTimeout(heartbeatTimeout);

-        heartbeatTimeout = setTimeout(() => {

-            sendHeartbeat();

-            schedulePeriodicHeartbeat();

+    function schedulePeriodicHeartbeat() {
+        if (destroyed || pageSuspended) return;
+        if (heartbeatTimeout) clearTimeout(heartbeatTimeout);
+        heartbeatTimeout = setTimeout(() => {
+            if (destroyed || pageSuspended) return;
+            sendHeartbeat();
+            schedulePeriodicHeartbeat();
         }, HEARTBEAT_INTERVAL_VAL);

     }

 

-    function scheduleProactiveHeartbeat() {

-        if (proactiveHeartbeatTimeout) clearTimeout(proactiveHeartbeatTimeout);

-        proactiveHeartbeatTimeout = setTimeout(() => {

-            sendHeartbeat();

+    function scheduleProactiveHeartbeat() {
+        if (destroyed || pageSuspended) return;
+        if (proactiveHeartbeatTimeout) clearTimeout(proactiveHeartbeatTimeout);
+        proactiveHeartbeatTimeout = setTimeout(() => {
+            if (destroyed || pageSuspended) return;
+            sendHeartbeat();
             schedulePeriodicHeartbeat(); // Reschedules the next periodic check to be exactly 15s from now

         }, 500); // 500ms stabilization delay

     }

@@ -1599,30 +1683,104 @@
     setupListeners();

 

     // Maintain a persistent keep-alive port connection to prevent background SW suspension

-    let keepAlivePort = null;

-    function connectKeepAlivePort() {

-        try {

+    let keepAlivePort = null;
+    function connectKeepAlivePort() {
+        if (destroyed || pageSuspended) return;
+        try {
             if (chrome.runtime.id) {

                 keepAlivePort = chrome.runtime.connect({ name: 'keepAlive' });

-                keepAlivePort.onDisconnect.addListener(() => {

-                    keepAlivePort = null;

-                    setTimeout(connectKeepAlivePort, 1000);

-                });

+                keepAlivePort.onDisconnect.addListener(() => {
+                    keepAlivePort = null;
+                    if (!destroyed && !pageSuspended) scheduleLifecycleTimeout(connectKeepAlivePort, 1000);
+                });
             }

         } catch (_e) {

-            // Extension context invalidated or disabled

-        }

-    }

-    connectKeepAlivePort();

+            // Extension context invalidated or disabled
+        }
+    }
+
+    function destroyContentScript() {
+        if (destroyed) return;
+        destroyed = true;
+
+        try {
+            window.postMessage({ __koalaPageApiSeek: PAGE_API_SEEK_BRIDGE, kind: 'destroy' }, '*');
+        } catch (_e) { /* page is already tearing down */ }
+        window.KOALA_PAGE_API_SEEK_ENABLED = false;
+
+        for (const timer of Object.values(_suppressTimers)) clearTimeout(timer);
+        _suppressTimers = {};
+        for (const timer of lifecycleTimeouts) clearTimeout(timer);
+        lifecycleTimeouts.clear();
+        for (const timer of seekPollTimers) clearInterval(timer);
+        seekPollTimers.clear();
+
+        if (hcmDialogTimer) { clearTimeout(hcmDialogTimer); hcmDialogTimer = null; }
+        if (episodeTransitionDebounce) { clearTimeout(episodeTransitionDebounce); episodeTransitionDebounce = null; }
+        if (seekDebounceTimer) { clearTimeout(seekDebounceTimer); seekDebounceTimer = null; }
+        if (playPauseCoalesceTimer) { clearTimeout(playPauseCoalesceTimer); playPauseCoalesceTimer = null; }
+        if (observerTimeout) { clearTimeout(observerTimeout); observerTimeout = null; }
+        if (heartbeatTimeout) { clearTimeout(heartbeatTimeout); heartbeatTimeout = null; }
+        if (proactiveHeartbeatTimeout) { clearTimeout(proactiveHeartbeatTimeout); proactiveHeartbeatTimeout = null; }
+        stopLobbyPoll();
+        pendingPlayPauseAction = null;
+        hcmDeferredSnapPending = false;
+
+        observer.disconnect();
+        if (keepAlivePort) {
+            try { keepAlivePort.disconnect(); } catch (_e) { /* already disconnected */ }
+            keepAlivePort = null;
+        }
+
+        for (const video of attachedVideos) {
+            const handlers = video._koalaHandlers;
+            if (handlers) {
+                video.removeEventListener('play', handlers.play);
+                video.removeEventListener('pause', handlers.pause);
+                video.removeEventListener('seeked', handlers.seeked);
+                video.removeEventListener('loadeddata', handlers.loadeddata);
+                if (handlers.waiting) video.removeEventListener('waiting', handlers.waiting);
+                delete video._koalaHandlers;
+            }
+            delete video.dataset.koalaAttached;
+        }
+        attachedVideos.clear();
+
+        document.removeEventListener('keydown', _hcmGesture, true);
+        document.removeEventListener('pointerdown', _hcmGesture, true);
+        document.removeEventListener('visibilitychange', handleVisibilityChange);
+        window.removeEventListener('pagehide', handlePageHide);
+        window.removeEventListener('pageshow', handlePageShow);
+        window.removeEventListener('message', handlePageApiTime);
+        if (hcmBadgeDomReadyHandler) {
+            document.removeEventListener('DOMContentLoaded', hcmBadgeDomReadyHandler);
+            hcmBadgeDomReadyHandler = null;
+        }
+
+        hcmRemoveDialog();
+        hcmRemoveBadge();
+        bypassCurrentAudioProcessing();
+        closeAudioContext();
+        try { window.koalaSyncChatOverlay?.destroy?.(); } catch (_e) { /* invalidated chat context */ }
+
+        try { chrome.storage.onChanged.removeListener(handleStorageChanged); } catch (_e) { /* invalidated context */ }
+        try { chrome.runtime.onMessage.removeListener(handleRuntimeMessage); } catch (_e) { /* invalidated context */ }
+
+        window.koalaSyncInjected = false;
+        delete window.koalaSyncContentController;
+    }
+
+    window.koalaSyncContentController = { destroy: destroyContentScript };
+    connectKeepAlivePort();
 

     schedulePeriodicHeartbeat();

 

     // Immediate heartbeat on injection — populate peer data without waiting 15s

-    setTimeout(() => sendHeartbeat(), 300);

+    scheduleLifecycleTimeout(() => sendHeartbeat(), 300);
 

     // Episode Auto-Sync: Boot recovery — check if background has an active lobby

-    chrome.runtime.sendMessage({ type: 'CONTENT_BOOT' }, (res) => {

-        if (chrome.runtime.lastError) return;

+    runtimeMessage({ type: 'CONTENT_BOOT' }, (res) => {
+        if (destroyed || chrome.runtime.lastError) return;
         if (res && res.lobbyActive && res.expectedTitle) {

             reportLog(`Boot: Active lobby detected for "${res.expectedTitle}"`, 'info');

             startLobbyPoll(res.expectedTitle);

@@ -1631,8 +1789,8 @@
 

     // Host Control Mode: fetch current room mode/role on injection (we may have

     // been injected after ROOM_DATA already arrived, missing the broadcast).

-    chrome.runtime.sendMessage({ type: 'GET_CONTROL_MODE' }, (res) => {

-        if (chrome.runtime.lastError || !res) return;

+    runtimeMessage({ type: 'GET_CONTROL_MODE' }, (res) => {
+        if (destroyed || chrome.runtime.lastError || !res) return;
         hcmControlMode = res.controlMode || 'everyone';

         hcmAmController = !!res.amController;

         hcmHostPeerId = res.hostPeerId || null;

@@ -1647,8 +1805,8 @@
     });

 

     // Pull localized strings for the in-page dialog/badge (English fallback above).

-    chrome.runtime.sendMessage({ type: 'GET_HCM_STRINGS' }, (res) => {

-        if (chrome.runtime.lastError || !res) return;

+    runtimeMessage({ type: 'GET_HCM_STRINGS' }, (res) => {
+        if (destroyed || chrome.runtime.lastError || !res) return;
         Object.keys(hcmStrings).forEach(k => { if (res[k]) hcmStrings[k] = res[k]; });

         // If the badge is already showing (early desync), refresh its text in place.

         // Re-creating the host element nukes the click target mid-poll and can drop a

diff --git a/extension/locales/de.json b/extension/locales/de.json
index de9a16f..94a3131 100644
--- a/extension/locales/de.json
+++ b/extension/locales/de.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Nachricht schreiben...",
   "CHAT_SEND": "Senden",
   "CHAT_MISSING_KEY": "Chat ist nur über einen aktuellen Einladungslink verfügbar.",
-  "CHAT_TOO_LONG": "Maximal 500 Zeichen.",
+  "CHAT_TOO_LONG": "Maximal 5000 Zeichen.",
   "CHAT_SEND_FAILED": "Nachricht konnte nicht gesendet werden.",
   "CHAT_EMPTY": "Noch keine Nachrichten. Der Chat ist nur live.",
   "LABEL_CHAT_NOTIFICATIONS": "Chat-Benachrichtigungen",
diff --git a/extension/locales/en.json b/extension/locales/en.json
index 7d215e9..dcd5e7b 100644
--- a/extension/locales/en.json
+++ b/extension/locales/en.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Write a message...",
   "CHAT_SEND": "Send",
   "CHAT_MISSING_KEY": "Chat is available only through a current invite link.",
-  "CHAT_TOO_LONG": "Maximum 500 characters.",
+  "CHAT_TOO_LONG": "Maximum 5000 characters.",
   "CHAT_SEND_FAILED": "Message could not be sent.",
   "CHAT_EMPTY": "No messages yet. Chat is live only.",
   "LABEL_CHAT_NOTIFICATIONS": "Chat Notifications",
diff --git a/extension/locales/es.json b/extension/locales/es.json
index 45bbbec..c42aedb 100644
--- a/extension/locales/es.json
+++ b/extension/locales/es.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Escribe un mensaje...",
   "CHAT_SEND": "Enviar",
   "CHAT_MISSING_KEY": "El chat solo está disponible mediante un enlace de invitación actual.",
-  "CHAT_TOO_LONG": "Máximo 500 caracteres.",
+  "CHAT_TOO_LONG": "Máximo 5000 caracteres.",
   "CHAT_SEND_FAILED": "No se pudo enviar el mensaje.",
   "CHAT_EMPTY": "Aún no hay mensajes. El chat solo es en directo.",
   "LABEL_CHAT_NOTIFICATIONS": "Notificaciones del chat",
diff --git a/extension/locales/fr.json b/extension/locales/fr.json
index 28875fa..83533a3 100644
--- a/extension/locales/fr.json
+++ b/extension/locales/fr.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Écrire un message...",
   "CHAT_SEND": "Envoyer",
   "CHAT_MISSING_KEY": "Le chat est disponible uniquement via un lien d'invitation actuel.",
-  "CHAT_TOO_LONG": "500 caractères maximum.",
+  "CHAT_TOO_LONG": "5000 caractères maximum.",
   "CHAT_SEND_FAILED": "Le message n'a pas pu être envoyé.",
   "CHAT_EMPTY": "Aucun message. Le chat est uniquement en direct.",
   "LABEL_CHAT_NOTIFICATIONS": "Notifications du chat",
diff --git a/extension/locales/it.json b/extension/locales/it.json
index 9d31954..8a3c1e5 100644
--- a/extension/locales/it.json
+++ b/extension/locales/it.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Scrivi un messaggio...",
   "CHAT_SEND": "Invia",
   "CHAT_MISSING_KEY": "La chat è disponibile solo tramite un link di invito attuale.",
-  "CHAT_TOO_LONG": "Massimo 500 caratteri.",
+  "CHAT_TOO_LONG": "Massimo 5000 caratteri.",
   "CHAT_SEND_FAILED": "Impossibile inviare il messaggio.",
   "CHAT_EMPTY": "Nessun messaggio. La chat è solo in diretta.",
   "LABEL_CHAT_NOTIFICATIONS": "Notifiche chat",
diff --git a/extension/locales/ja.json b/extension/locales/ja.json
index 8db139c..383657c 100644
--- a/extension/locales/ja.json
+++ b/extension/locales/ja.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "メッセージを入力...",
   "CHAT_SEND": "送信",
   "CHAT_MISSING_KEY": "チャットは最新の招待リンクからのみ利用できます。",
-  "CHAT_TOO_LONG": "最大500文字です。",
+  "CHAT_TOO_LONG": "最大5000文字です。",
   "CHAT_SEND_FAILED": "メッセージを送信できませんでした。",
   "CHAT_EMPTY": "まだメッセージはありません。チャットはライブのみです。",
   "LABEL_CHAT_NOTIFICATIONS": "チャット通知",
diff --git a/extension/locales/ko.json b/extension/locales/ko.json
index d77a27a..ee7c353 100644
--- a/extension/locales/ko.json
+++ b/extension/locales/ko.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "메시지를 입력하세요...",
   "CHAT_SEND": "보내기",
   "CHAT_MISSING_KEY": "채팅은 최신 초대 링크를 통해서만 사용할 수 있습니다.",
-  "CHAT_TOO_LONG": "최대 500자입니다.",
+  "CHAT_TOO_LONG": "최대 5000자입니다.",
   "CHAT_SEND_FAILED": "메시지를 보낼 수 없습니다.",
   "CHAT_EMPTY": "아직 메시지가 없습니다. 채팅은 실시간 전용입니다.",
   "LABEL_CHAT_NOTIFICATIONS": "채팅 알림",
diff --git a/extension/locales/nl.json b/extension/locales/nl.json
index 231d014..bb56eac 100644
--- a/extension/locales/nl.json
+++ b/extension/locales/nl.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Schrijf een bericht...",
   "CHAT_SEND": "Verzenden",
   "CHAT_MISSING_KEY": "Chat is alleen beschikbaar via een actuele uitnodigingslink.",
-  "CHAT_TOO_LONG": "Maximaal 500 tekens.",
+  "CHAT_TOO_LONG": "Maximaal 5000 tekens.",
   "CHAT_SEND_FAILED": "Bericht kon niet worden verzonden.",
   "CHAT_EMPTY": "Nog geen berichten. Chat is alleen live.",
   "LABEL_CHAT_NOTIFICATIONS": "Chatmeldingen",
diff --git a/extension/locales/pl.json b/extension/locales/pl.json
index 18ece3a..b1148ef 100644
--- a/extension/locales/pl.json
+++ b/extension/locales/pl.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Napisz wiadomość...",
   "CHAT_SEND": "Wyślij",
   "CHAT_MISSING_KEY": "Czat jest dostępny tylko przez aktualny link zaproszenia.",
-  "CHAT_TOO_LONG": "Maksymalnie 500 znaków.",
+  "CHAT_TOO_LONG": "Maksymalnie 5000 znaków.",
   "CHAT_SEND_FAILED": "Nie udało się wysłać wiadomości.",
   "CHAT_EMPTY": "Brak wiadomości. Czat działa tylko na żywo.",
   "LABEL_CHAT_NOTIFICATIONS": "Powiadomienia czatu",
diff --git a/extension/locales/pt-BR.json b/extension/locales/pt-BR.json
index ac9dffc..0220416 100644
--- a/extension/locales/pt-BR.json
+++ b/extension/locales/pt-BR.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Escreva uma mensagem...",
   "CHAT_SEND": "Enviar",
   "CHAT_MISSING_KEY": "O chat está disponível apenas por um link de convite atual.",
-  "CHAT_TOO_LONG": "Máximo de 500 caracteres.",
+  "CHAT_TOO_LONG": "Máximo de 5000 caracteres.",
   "CHAT_SEND_FAILED": "Não foi possível enviar a mensagem.",
   "CHAT_EMPTY": "Ainda não há mensagens. O chat é somente ao vivo.",
   "LABEL_CHAT_NOTIFICATIONS": "Notificações do chat",
diff --git a/extension/locales/pt.json b/extension/locales/pt.json
index 7e980ef..710c2c4 100644
--- a/extension/locales/pt.json
+++ b/extension/locales/pt.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Escreva uma mensagem...",
   "CHAT_SEND": "Enviar",
   "CHAT_MISSING_KEY": "O chat está disponível apenas através de um link de convite atual.",
-  "CHAT_TOO_LONG": "Máximo de 500 caracteres.",
+  "CHAT_TOO_LONG": "Máximo de 5000 caracteres.",
   "CHAT_SEND_FAILED": "Não foi possível enviar a mensagem.",
   "CHAT_EMPTY": "Ainda não há mensagens. O chat funciona apenas em direto.",
   "LABEL_CHAT_NOTIFICATIONS": "Notificações do chat",
diff --git a/extension/locales/ru.json b/extension/locales/ru.json
index 0d3f607..3bb12b8 100644
--- a/extension/locales/ru.json
+++ b/extension/locales/ru.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Напишите сообщение...",
   "CHAT_SEND": "Отправить",
   "CHAT_MISSING_KEY": "Чат доступен только по актуальной ссылке-приглашению.",
-  "CHAT_TOO_LONG": "Не более 500 символов.",
+  "CHAT_TOO_LONG": "Не более 5000 символов.",
   "CHAT_SEND_FAILED": "Не удалось отправить сообщение.",
   "CHAT_EMPTY": "Сообщений пока нет. Чат работает только в реальном времени.",
   "LABEL_CHAT_NOTIFICATIONS": "Уведомления чата",
diff --git a/extension/locales/tr.json b/extension/locales/tr.json
index 3796f41..0f32aca 100644
--- a/extension/locales/tr.json
+++ b/extension/locales/tr.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Bir mesaj yazın...",
   "CHAT_SEND": "Gönder",
   "CHAT_MISSING_KEY": "Sohbet yalnızca güncel bir davet bağlantısıyla kullanılabilir.",
-  "CHAT_TOO_LONG": "En fazla 500 karakter.",
+  "CHAT_TOO_LONG": "En fazla 5000 karakter.",
   "CHAT_SEND_FAILED": "Mesaj gönderilemedi.",
   "CHAT_EMPTY": "Henüz mesaj yok. Sohbet yalnızca canlıdır.",
   "LABEL_CHAT_NOTIFICATIONS": "Sohbet bildirimleri",
diff --git a/extension/locales/uk.json b/extension/locales/uk.json
index 35638b4..2c5a918 100644
--- a/extension/locales/uk.json
+++ b/extension/locales/uk.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "Напишіть повідомлення...",
   "CHAT_SEND": "Надіслати",
   "CHAT_MISSING_KEY": "Чат доступний лише за актуальним посиланням-запрошенням.",
-  "CHAT_TOO_LONG": "Не більше 500 символів.",
+  "CHAT_TOO_LONG": "Не більше 5000 символів.",
   "CHAT_SEND_FAILED": "Не вдалося надіслати повідомлення.",
   "CHAT_EMPTY": "Повідомлень ще немає. Чат працює лише наживо.",
   "LABEL_CHAT_NOTIFICATIONS": "Сповіщення чату",
diff --git a/extension/locales/zh.json b/extension/locales/zh.json
index 8d3f21a..c76220f 100644
--- a/extension/locales/zh.json
+++ b/extension/locales/zh.json
@@ -277,7 +277,7 @@
   "CHAT_PLACEHOLDER": "输入消息...",
   "CHAT_SEND": "发送",
   "CHAT_MISSING_KEY": "聊天仅可通过当前邀请链接使用。",
-  "CHAT_TOO_LONG": "最多500个字符。",
+  "CHAT_TOO_LONG": "最多5000个字符。",
   "CHAT_SEND_FAILED": "无法发送消息。",
   "CHAT_EMPTY": "暂无消息。聊天仅实时显示。",
   "LABEL_CHAT_NOTIFICATIONS": "聊天通知",
diff --git a/extension/target-tab-lifecycle.test.mjs b/extension/target-tab-lifecycle.test.mjs
new file mode 100644
index 0000000..5b60dab
--- /dev/null
+++ b/extension/target-tab-lifecycle.test.mjs
@@ -0,0 +1,70 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+
+const extensionDir = path.dirname(fileURLToPath(import.meta.url));
+const backgroundSource = fs.readFileSync(path.join(extensionDir, 'background.js'), 'utf8');
+const contentSource = fs.readFileSync(path.join(extensionDir, 'content.js'), 'utf8');
+const overlaySource = fs.readFileSync(path.join(extensionDir, 'chat-overlay.js'), 'utf8');
+
+describe('target tab lifecycle', () => {
+    it('injects playback and chat scripts only into the explicitly selected tab', () => {
+        expect(backgroundSource).not.toContain('chrome.tabs.onActivated');
+        expect(backgroundSource).not.toContain('chrome.tabs.query({})');
+        expect(backgroundSource).toContain("target: { tabId }");
+        expect(backgroundSource).toContain("files: ['chat-format.js', 'chat-overlay.js', 'content.js']");
+        expect(backgroundSource).toContain("chrome.tabs.query({ url: 'https://sync.koalastuff.net/*' })");
+
+        const activationStart = backgroundSource.indexOf('async function activateTargetTab');
+        const activationEnd = backgroundSource.indexOf('async function reactivateCurrentTarget', activationStart);
+        const activationSource = backgroundSource.slice(activationStart, activationEnd);
+        expect(activationSource.indexOf('await deactivateTargetTab(previousTabId)'))
+            .toBeLessThan(activationSource.indexOf('await injectContentScript(selectedTabId'));
+        expect(activationSource).toContain('previousTabId !== selectedTabId');
+        expect(contentSource).toContain('if (window.koalaSyncInjected && chrome.runtime.id)');
+        expect(overlaySource).toContain('if (window.koalaSyncChatOverlay?.refresh)');
+    });
+
+    it('fully deactivates old and superseded target injections', () => {
+        expect(backgroundSource).toContain("chrome.tabs.sendMessage(normalizedTabId, { type: 'TARGET_DEACTIVATE' })");
+        expect(backgroundSource.match(/await deactivateTargetTab\(selectedTabId\)/g)?.length).toBeGreaterThanOrEqual(4);
+        expect(contentSource).toContain("if (message.type === 'TARGET_DEACTIVATE')");
+        expect(overlaySource).toContain("message?.type === 'TARGET_DEACTIVATE'");
+    });
+
+    it('tears down every persistent content-script resource', () => {
+        expect(contentSource).toContain('function destroyContentScript()');
+        expect(contentSource).toContain('observer.disconnect()');
+        expect(contentSource).toContain('keepAlivePort.disconnect()');
+        expect(contentSource).toContain('for (const video of attachedVideos)');
+        expect(contentSource).toContain("document.removeEventListener('visibilitychange', handleVisibilityChange)");
+        expect(contentSource).toContain("window.removeEventListener('pagehide', handlePageHide)");
+        expect(contentSource).toContain("window.removeEventListener('pageshow', handlePageShow)");
+        expect(contentSource).toContain('chrome.storage.onChanged.removeListener(handleStorageChanged)');
+        expect(contentSource).toContain('chrome.runtime.onMessage.removeListener(handleRuntimeMessage)');
+        expect(contentSource).toContain('window.koalaSyncInjected = false');
+    });
+
+    it('stops the MAIN-world seek bridge when its target is deactivated', () => {
+        expect(backgroundSource).toContain('const timelineInterval = setInterval');
+        expect(backgroundSource).toContain('clearInterval(timelineInterval)');
+        expect(backgroundSource).toContain("window.removeEventListener('message', handleBridgeMessage)");
+        expect(contentSource).toContain("kind: 'destroy'");
+    });
+
+    it('self-cleans instead of throwing when an extension reload invalidates the context', () => {
+        expect(contentSource).toContain('if (!chrome.runtime?.id)');
+        expect(contentSource).toContain('destroyContentScript()');
+        expect(contentSource).toContain('return chrome.runtime.sendMessage(message, callback) || Promise.resolve(undefined)');
+        expect(contentSource).toContain('function handleVisibilityChange()');
+    });
+
+    it('suspends background work for bfcache and restores it without duplicate injection', () => {
+        expect(contentSource).toContain('pageSuspended = true');
+        expect(contentSource).toContain('if (destroyed || pageSuspended) return');
+        expect(contentSource).toContain('if (!destroyed && !pageSuspended) scheduleLifecycleTimeout(connectKeepAlivePort, 1000)');
+        expect(contentSource).toMatch(/function handlePageShow\(event\)[\s\S]*if \(!event\.persisted\) return;[\s\S]*pageSuspended = false/);
+        expect(contentSource).toMatch(/function handlePageShow\(event\)[\s\S]*observer\.observe\(document\.documentElement[\s\S]*setupListeners\(\)[\s\S]*connectKeepAlivePort\(\)/);
+    });
+});