docs: update all docs for lazy-connect, refactor, and .cjs rename

- ARCHITECTURE.md: startup -> lazy connect, reconnect when in room
- HOW_IT_WORKS.md: on-demand connection, heartbeat while connected
- PRIVACY.md: clarify alarms only during active sessions
- SYNC_GUIDE.md: build-extension.cjs + episode-utils injection
- StoreDescription.md: on-demand relay, no persistent connection
- README.md + extension/README.md: npm run build:extension
- extension/README.md: replace Dual Heartbeat with On-Demand Connection
- website/privacy.html: add lazy-connect privacy note

docs/ARCHITECTURE.md

@@ -2,9 +2,10 @@
 
 This document describes the communication flows and internal logic of the KoalaSync system.
 
-## 1. Extension Startup & Connection
-- **Initialization**: On startup, `background.js` reads settings (Server URL, Username, Last Room) from `chrome.storage.sync`.
-- **WebSocket Handshake**:
+## 1. Extension Connection (Lazy Connect)
+- **Initialization**: On startup, `background.js` reads settings (Server URL, Username, Last Room) from `chrome.storage.sync`. No WebSocket connection is established at this point.
+- **On-Demand Connection**: The extension only connects when needed — either the user opens the popup with saved room credentials, or when actively in a room. When not in a room, no connection exists. This improves privacy (IP not exposed while idle) and reduces battery/network usage.
+- **WebSocket Handshake (when connecting)**:
   1. Background creates a `new WebSocket` to `/socket.io/?EIO=4&transport=websocket&version=1.0.0`.
   2. Server performs security checks:
      - **IP Rate Limit**: Checks if the IP has exceeded connection limits.
@@ -45,7 +46,7 @@ To maintain a clean room state and eliminate "Ghost Peers":
 - **Video Heartbeat (Content)**: Every 15 seconds, `content.js` sends current playback metadata (time, title, state) if a video is found.
 - **Server Pruning**: The server runs a "Reaper" every 2 minutes. If a peer has sent **zero** activity (no events and no heartbeats) for 5 minutes, they are forcefully disconnected.
 - **Immediate Cleanup**: Rooms are deleted instantly when the last peer leaves or disconnects.
-- **Reconnect Strategy**: Aggressive backoff — 500ms base, 1.5x multiplier, capped at 5s. Max 20 attempts before marking as failed. Events are queued during disconnect and flushed after namespace rejoin.
+- **Reconnect Strategy (while in room)**: Aggressive backoff — 500ms base, 1.5x multiplier, capped at 5s. Max 20 attempts before marking as failed. Events are queued during disconnect and flushed after namespace rejoin. When not in a room, no reconnection occurs.
 
 > [!CAUTION]
 > **Identity Rule**: Differentiate between `peerId` and `socket.id`. Use `socket.id` exclusively for ephemeral transport routing on the server. Use `peerId` exclusively for identity, state management, and room tracking across the stack.
@@ -70,5 +71,5 @@ KoalaSync uses a megaphone routing approach to minimize server logic:
 To maintain a "Single Source of Truth" across the server and extension without using a bundler:
 - **Relay Server & Extension Modules**: `background.js` and `popup.js` import constants directly from `shared/constants.js`.
 - **Content Scripts**: To ensure zero-latency execution, `content.js` uses a synchronized copy of `EVENTS` and constants.
-- **Automation**: The `node scripts/build-extension.js` script automatically injects these constants into `content.js` during the build process, eliminating the risk of manual mirror mismatch.
+- **Automation**: The `npm run build:extension` script automatically injects `EVENTS`, `HEARTBEAT_INTERVAL`, and `episode-utils.js` functions into `content.js` during the build process, eliminating the risk of manual mirror mismatch.
 - **Verification**: Any protocol change is automatically propagated across the stack by running the build script.

docs/HOW_IT_WORKS.md

@@ -16,9 +16,9 @@ This guide walks through the complete user flow of KoalaSync, from creating a ro
 
 ## Step 2: Connecting to the Relay Server
 
-When you open the extension popup, the background service worker connects to the relay server:
+When you open the extension popup (with saved room credentials) or when a saved room configuration exists from a previous session, the background service worker connects to the relay server:
 
-1. **WebSocket Handshake**: `background.js` opens a WebSocket to `wss://syncserver.koalastuff.net/socket.io/?EIO=4&transport=websocket`.
+1. **WebSocket Handshake** (on demand): `background.js` opens a WebSocket to `wss://syncserver.koalastuff.net/socket.io/?EIO=4&transport=websocket` only when needed (popup opened or active room).
 2. **Security Checks** (server-side):
    - The server checks the client's **IP rate limit** (max 10 connections per 60 seconds).
    - The server validates the **authentication token** (hardcoded in `shared/constants.js`) to verify this is a legitimate KoalaSync client.
@@ -155,7 +155,7 @@ While in a room, two heartbeats keep the session alive:
 
 | Heartbeat | Interval | Source | Purpose |
 |:----------|:---------|:-------|:--------|
-| **Background** | 30 seconds | `background.js` | Signals "I'm still connected" and triggers aggressive reconnect (500ms base, max 5s) |
+| **Background** | 30 seconds | `background.js` | While connected, signals "I'm still connected" and triggers automatic reconnect (500ms base, max 5s). No heartbeats fire when idle (lazy connect). |
 | **Content** | 15 seconds | `content.js` | Sends video metadata: `currentTime`, `mediaTitle`, `playbackState`, `volume`, `muted` |
 
 - **Server Reaper**: Every 2 minutes, the server checks for peers with no activity for 5+ minutes and disconnects them ("dead peer pruning").

docs/PRIVACY.md

@@ -33,7 +33,7 @@ The browser extension requires the following permissions:
 - `storage`: To remember your local preferences (username, server URL, room settings).
 - `tabs` & `scripting`: To detect and control video elements on the pages you choose to sync.
 - `<all_urls>` (host permission): Required to detect `<video>` elements on any website the user chooses to synchronize. The extension only activates on the specific tab the user has actively selected — it does not scan, monitor, or interact with any other tabs or pages.
-- `alarms`: To keep the background service worker alive during active sync sessions.
+- `alarms`: To keep the background service worker alive during active sync sessions (the extension only stays connected while you are in a room).
 - `notifications`: To display sync status updates (e.g., "Peer joined", "Force Sync initiated").
 - **No History Access**: We do not read, store, or transmit your browsing history. We only interact with the specific tab you have actively selected for synchronization.
 

docs/SYNC_GUIDE.md

@@ -17,13 +17,15 @@ You MUST run the build script in any of the following scenarios:
 
 Run the Node.js build script from the repository root:
 ```bash
-node scripts/build-extension.js
+node scripts/build-extension.cjs
+# or simply:
+npm run build:extension
 ```
 
 ## What does it do?
 The build script performs the following actions:
 1. Synchronizes protocol constants by copying `shared/constants.js`, `shared/blacklist.js`, and `shared/README.md` into `extension/shared/`.
-2. Injects `EVENTS` and `HEARTBEAT_INTERVAL` into `content.js` via marker-based replacement.
+2. Injects `EVENTS`, `HEARTBEAT_INTERVAL`, and `episode-utils.js` functions (`extractEpisodeId`, `sameEpisode`) into `content.js` via marker-based replacement.
 3. Compiles browser-specific manifest files.
 4. Packages the final ready-to-publish extension artifacts for Chrome and Firefox into the `dist/` directory.