diff --git a/src/background/index.ts b/src/background/index.ts
index d277dcb..95c8023 100644
--- a/src/background/index.ts
+++ b/src/background/index.ts
@@ -16,6 +16,16 @@ let isRecording = false;
 let offscreenCreated = false;
 let lastScreenshotTime = 0;
 let cachedScreenshot: Blob | null = null;
+// Port from offscreen (D-17). Re-assigned on every (re)connect.
+let videoPort: chrome.runtime.Port | null = null;
+// Offscreen readiness Promise — set up at module load, resolved on first
+// OFFSCREEN_READY message (Pattern 4). startVideoCapture awaits this before
+// sending START_RECORDING, so we never lose the popup's transient activation
+// to a race with the offscreen bootstrap.
+let offscreenReadyResolve: (() => void) | null = null;
+let offscreenReady: Promise<void> = new Promise((res) => {
+  offscreenReadyResolve = res;
+});
 // userEvents хранится только в content script
 // Для архивации получаем его оттуда
 
@@ -54,6 +64,61 @@ async function ensureOffscreen() {
   }
 }
 
+// SW-side port host (D-17, RESEARCH.md Pattern 5). The offscreen opens this
+// port on bootstrap and reconnects on disconnect. We use it for: (a)
+// keepalive traffic (PING) — Chrome 110+ resets the SW idle timer on every
+// port message; (b) on-demand REQUEST_BUFFER round-trip during SAVE_ARCHIVE.
+chrome.runtime.onConnect.addListener((port) => {
+  // T-1-04 mitigation: only accept ports from this extension
+  if (port.name !== 'video-keepalive') {
+    return;
+  }
+  if (port.sender?.id !== chrome.runtime.id) {
+    logger.warn('Rejecting port with mismatched sender:', port.sender?.id);
+    port.disconnect();
+    return;
+  }
+  logger.log('Offscreen port connected');
+  videoPort = port;
+  port.onDisconnect.addListener(() => {
+    logger.log('Offscreen port disconnected; offscreen will reconnect');
+    videoPort = null;
+  });
+  // Inbound traffic is mostly PING (ignored) and BUFFER (handled by the
+  // per-request listener installed in getVideoBufferFromOffscreen).
+});
+
+const BUFFER_FETCH_TIMEOUT_MS = 2_000;
+
+async function getVideoBufferFromOffscreen(): Promise<VideoBufferResponse> {
+  if (videoPort === null) {
+    logger.warn('No offscreen port available; returning empty buffer');
+    return { chunks: [] };
+  }
+  const port = videoPort;
+  return new Promise<VideoBufferResponse>((resolve) => {
+    const timer = setTimeout(() => {
+      port.onMessage.removeListener(handler);
+      logger.warn(`Buffer fetch timed out after ${BUFFER_FETCH_TIMEOUT_MS} ms`);
+      resolve({ chunks: [] });
+    }, BUFFER_FETCH_TIMEOUT_MS);
+    const handler = (msg: unknown) => {
+      if (
+        typeof msg === 'object' &&
+        msg !== null &&
+        (msg as { type?: unknown }).type === 'BUFFER'
+      ) {
+        clearTimeout(timer);
+        port.onMessage.removeListener(handler);
+        const chunks = (msg as { chunks?: VideoChunk[] }).chunks ?? [];
+        resolve({ chunks });
+      }
+    };
+    port.onMessage.addListener(handler);
+    port.postMessage({ type: 'REQUEST_BUFFER' });
+  });
+}
+
 // Начало записи видео
 async function startVideoCapture() {
   if (isRecording) {
@@ -73,6 +138,11 @@ async function startVideoCapture() {
 
     // Создаём offscreen документ (с reason из D-02)
     await ensureOffscreen();
+    // Ждём, пока offscreen зарегистрирует свой onMessage listener
+    // (RESEARCH.md Pattern 4). Иначе гонка: START_RECORDING летит раньше,
+    // чем offscreen готов его принять, и Chrome бросает "Receiving end
+    // does not exist".
+    await offscreenReady;
 
     // Просим offscreen запустить запись — getDisplayMedia вызывается там
     // (D-01: больше нет SW-side stream-id юзаства).
@@ -101,11 +171,8 @@ async function startVideoCapture() {
 // Старая alarms-based реализация удалена: alarm callbacks не сбрасывали SW idle
 // timer (audit P1 #8), а порт сбрасывает таймер на каждое сообщение.
 
-// Получение видеобуфера (временный синхронный стаб; Task 2 заменит его
-// на асинхронный запрос к offscreen через long-lived port).
-function getVideoBuffer(): VideoBufferResponse {
-  return { chunks: [] };
-}
+// Получение видеобуфера — port-based (getVideoBufferFromOffscreen объявлен
+// выше). Старый синхронный SW-локальный буфер удалён в Task 1 этого плана.
 
 // Получение скриншота активной вкладки
 async function captureScreenshot(): Promise<Blob> {
@@ -264,9 +331,9 @@ async function saveArchive() {
     logger.log('Capturing screenshot...');
     const screenshot = await captureScreenshot();
 
-    // Получаем видео буфер
-    const videoBuffer = getVideoBuffer();
-    logger.log(`Video buffer: ${videoBuffer.chunks.length} chunks`);
+    // Получаем видео буфер из offscreen через long-lived port (D-17)
+    const videoBufferResp = await getVideoBufferFromOffscreen();
+    logger.log(`Video buffer: ${videoBufferResp.chunks.length} chunks`);
 
     // Получаем rrweb события от content script
     logger.log(`Requesting rrweb events from content script on tab ${tab.id} (${tab.url})...`);
@@ -303,7 +370,7 @@ async function saveArchive() {
 
     // Создаем архив
     const archiveBlob = await createArchive(
-      videoBuffer,
+      videoBufferResp,
       rrwebEvents,
       userEvents,
       screenshot
@@ -327,7 +394,14 @@ async function saveArchive() {
 // REQUEST_PERMISSIONS теперь просто запускает запись и возвращает granted=true.
 
 // Обработка сообщений
-chrome.runtime.onMessage.addListener((message: Message, _sender, sendResponse) => {
+chrome.runtime.onMessage.addListener((message: Message, sender, sendResponse) => {
+  // T-1-NEW-05-01 mitigation: only accept onMessage traffic from this
+  // extension (popup, content script, offscreen). External callers (other
+  // extensions, web pages) are silently dropped.
+  if (sender.id !== chrome.runtime.id) {
+    logger.warn('Rejecting message with mismatched sender:', sender.id);
+    return false;
+  }
   logger.log('Received message:', message.type, message);
 
   switch (message.type) {
@@ -349,8 +423,8 @@ chrome.runtime.onMessage.addListener((message: Message, _sender, sendResponse) =
       return true;
 
     case 'GET_VIDEO_BUFFER':
-      sendResponse(getVideoBuffer());
-      return false;
+      getVideoBufferFromOffscreen().then((resp) => sendResponse(resp));
+      return true;
 
     case 'SAVE_ARCHIVE':
       saveArchive().then(result => {
@@ -358,6 +432,12 @@ chrome.runtime.onMessage.addListener((message: Message, _sender, sendResponse) =
       });
       return true;
 
+    case 'OFFSCREEN_READY':
+      logger.log('OFFSCREEN_READY received');
+      offscreenReadyResolve?.();
+      offscreenReadyResolve = null;
+      return false;
+
     // Legacy chunk-streaming and IndexedDB save/load handlers were removed
     // in Plan 01-03:
     //   - the offscreen recorder now owns the buffer (D-16);
@@ -373,14 +453,38 @@ chrome.runtime.onMessage.addListener((message: Message, _sender, sendResponse) =
 });
 
 // Инициализация
-function initialize() {
+async function initialize() {
   logger.log('Service Worker initializing');
+  // Audit P1 #8: after the SW respawns (e.g. after Chrome wakes it from idle),
+  // the offscreen document may still exist while our offscreenCreated flag
+  // resets to false. Ask Chrome the ground truth so we don't end up trying
+  // to createDocument over an existing one. Cheap and idempotent.
+  try {
+    if (typeof chrome.offscreen?.hasDocument === 'function') {
+      const exists = await chrome.offscreen.hasDocument();
+      if (exists) {
+        offscreenCreated = true;
+        logger.log('Existing offscreen document detected on SW init');
+      }
+    }
+  } catch (err) {
+    logger.warn('chrome.offscreen.hasDocument check failed:', err);
+  }
   logger.log('Service Worker initialized');
 }
 
 // Запуск при установке
 chrome.runtime.onInstalled.addListener((details) => {
   logger.log('Extension installed/updated:', details.reason);
+  // RESEARCH.md Runtime State Inventory — clean up orphaned IndexedDB from
+  // pre-Phase-01 builds. Idempotent: no-op if DB never existed.
+  // T-1-NEW-05-02 mitigation.
+  try {
+    indexedDB.deleteDatabase('VideoRecorderDB');
+    logger.log('Cleaned up orphaned VideoRecorderDB (if present)');
+  } catch (e) {
+    logger.warn('IDB cleanup failed:', e);
+  }
   initialize();
 });