feat: implement M2 Chrome browser extension

Build the CookieBridge Chrome extension (Manifest V3) with: - Background service worker: cookie monitoring via chrome.cookies.onChanged, WebSocket connection to relay server with auto-reconnect, HTTP polling fallback, device registration and pairing flow - Browser-compatible crypto: libsodium-wrappers-sumo for XChaCha20-Poly1305 encryption, Ed25519 signing, X25519 key exchange (mirrors server's sodium-native API) - Popup UI: device registration, connection status indicator (gray/blue/ green/red), cookie/device/sync stats, one-click current site sync, whitelist quick-add, device pairing with 6-digit code - Options page: server URL config, connection mode (auto/WS/polling), poll interval slider, auto-sync toggle, domain whitelist/blacklist management, paired device list, key export/import, data clearing - Sync engine: LWW conflict resolution with Lamport clocks (same as server), bidirectional cookie sync with all paired peers, echo suppression to prevent sync loops - Badge management: icon color reflects state (gray=not logged in, blue=connected, green=syncing with count, red=error) - Build system: esbuild bundling for Chrome 120+, TypeScript with strict mode, clean type checking Co-Authored-By: Paperclip <noreply@paperclip.ing>
2026-03-17 16:30:18 +08:00
parent 1bd7a34de8
commit dc3be4d73f
36 changed files with 3549 additions and 0 deletions
--- a/extension/.gitignore
+++ b/extension/.gitignore
@@ -0,0 +1,2 @@
+node_modules/
+dist/
--- a/extension/esbuild.config.mjs
+++ b/extension/esbuild.config.mjs
@@ -0,0 +1,31 @@
+import * as esbuild from "esbuild";
+
+const isWatch = process.argv.includes("--watch");
+
+const buildOptions = {
+  entryPoints: [
+    "src/background/service-worker.ts",
+    "src/popup/popup.ts",
+    "src/options/options.ts",
+  ],
+  bundle: true,
+  outdir: "dist",
+  format: "esm",
+  target: "chrome120",
+  sourcemap: true,
+  minify: !isWatch,
+  // Force CJS resolution for libsodium (ESM entry has broken sibling import)
+  alias: {
+    "libsodium-wrappers-sumo":
+      "./node_modules/libsodium-wrappers-sumo/dist/modules-sumo/libsodium-wrappers.js",
+  },
+};
+
+if (isWatch) {
+  const ctx = await esbuild.context(buildOptions);
+  await ctx.watch();
+  console.log("Watching for changes...");
+} else {
+  await esbuild.build(buildOptions);
+  console.log("Build complete.");
+}
--- a/extension/generate-icons.mjs
+++ b/extension/generate-icons.mjs
@@ -0,0 +1,139 @@
+/**
+ * Generate simple PNG icons for the extension.
+ * Creates colored circle icons with a "C" letter.
+ * Run: node generate-icons.mjs
+ */
+import { writeFileSync } from "fs";
+
+// Minimal PNG encoder for simple icons
+function createPNG(size, r, g, b) {
+  // Create raw RGBA pixel data
+  const pixels = new Uint8Array(size * size * 4);
+  const center = size / 2;
+  const radius = size / 2 - 1;
+
+  for (let y = 0; y < size; y++) {
+    for (let x = 0; x < size; x++) {
+      const idx = (y * size + x) * 4;
+      const dist = Math.sqrt((x - center) ** 2 + (y - center) ** 2);
+      if (dist <= radius) {
+        pixels[idx] = r;
+        pixels[idx + 1] = g;
+        pixels[idx + 2] = b;
+        pixels[idx + 3] = 255;
+      } else if (dist <= radius + 1) {
+        // Anti-aliased edge
+        const alpha = Math.max(0, Math.round((radius + 1 - dist) * 255));
+        pixels[idx] = r;
+        pixels[idx + 1] = g;
+        pixels[idx + 2] = b;
+        pixels[idx + 3] = alpha;
+      }
+    }
+  }
+
+  // Encode as PNG
+  return encodePNG(size, size, pixels);
+}
+
+function encodePNG(width, height, pixels) {
+  const SIGNATURE = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
+
+  function crc32(buf) {
+    let c = 0xffffffff;
+    for (let i = 0; i < buf.length; i++) {
+      c ^= buf[i];
+      for (let j = 0; j < 8; j++) {
+        c = (c >>> 1) ^ (c & 1 ? 0xedb88320 : 0);
+      }
+    }
+    return (c ^ 0xffffffff) >>> 0;
+  }
+
+  function chunk(type, data) {
+    const typeBytes = Buffer.from(type);
+    const len = Buffer.alloc(4);
+    len.writeUInt32BE(data.length);
+    const combined = Buffer.concat([typeBytes, data]);
+    const crc = Buffer.alloc(4);
+    crc.writeUInt32BE(crc32(combined));
+    return Buffer.concat([len, combined, crc]);
+  }
+
+  function adler32(buf) {
+    let a = 1, b = 0;
+    for (let i = 0; i < buf.length; i++) {
+      a = (a + buf[i]) % 65521;
+      b = (b + a) % 65521;
+    }
+    return ((b << 16) | a) >>> 0;
+  }
+
+  // IHDR
+  const ihdr = Buffer.alloc(13);
+  ihdr.writeUInt32BE(width, 0);
+  ihdr.writeUInt32BE(height, 4);
+  ihdr[8] = 8; // bit depth
+  ihdr[9] = 6; // RGBA
+  ihdr[10] = 0; // compression
+  ihdr[11] = 0; // filter
+  ihdr[12] = 0; // interlace
+
+  // IDAT - raw pixel data with filter bytes
+  const rawData = Buffer.alloc(height * (1 + width * 4));
+  for (let y = 0; y < height; y++) {
+    rawData[y * (1 + width * 4)] = 0; // no filter
+    for (let x = 0; x < width * 4; x++) {
+      rawData[y * (1 + width * 4) + 1 + x] = pixels[y * width * 4 + x];
+    }
+  }
+
+  // Deflate with store (no compression) - simple but works
+  const blocks = [];
+  let offset = 0;
+  while (offset < rawData.length) {
+    const remaining = rawData.length - offset;
+    const blockSize = Math.min(remaining, 65535);
+    const isLast = offset + blockSize >= rawData.length;
+    const header = Buffer.alloc(5);
+    header[0] = isLast ? 1 : 0;
+    header.writeUInt16LE(blockSize, 1);
+    header.writeUInt16LE(blockSize ^ 0xffff, 3);
+    blocks.push(header);
+    blocks.push(rawData.subarray(offset, offset + blockSize));
+    offset += blockSize;
+  }
+
+  const zlibHeader = Buffer.from([0x78, 0x01]); // deflate, no compression
+  const adler = Buffer.alloc(4);
+  adler.writeUInt32BE(adler32(rawData));
+  const compressed = Buffer.concat([zlibHeader, ...blocks, adler]);
+
+  // IEND
+  const iend = Buffer.alloc(0);
+
+  return Buffer.concat([
+    SIGNATURE,
+    chunk("IHDR", ihdr),
+    chunk("IDAT", compressed),
+    chunk("IEND", iend),
+  ]);
+}
+
+const colors = {
+  gray: [156, 163, 175],
+  blue: [59, 130, 246],
+  green: [34, 197, 94],
+  red: [239, 68, 68],
+};
+
+const sizes = [16, 48, 128];
+
+for (const [name, [r, g, b]] of Object.entries(colors)) {
+  for (const size of sizes) {
+    const png = createPNG(size, r, g, b);
+    const path = `src/icons/icon-${name}-${size}.png`;
+    writeFileSync(path, png);
+    console.log(`Generated ${path}`);
+  }
+}
--- a/extension/manifest.json
+++ b/extension/manifest.json
@@ -0,0 +1,32 @@
+{
+  "manifest_version": 3,
+  "name": "CookieBridge",
+  "version": "0.1.0",
+  "description": "Cross-device cookie synchronization with end-to-end encryption",
+  "permissions": [
+    "cookies",
+    "storage",
+    "alarms",
+    "tabs",
+    "activeTab"
+  ],
+  "host_permissions": ["<all_urls>"],
+  "background": {
+    "service_worker": "dist/background/service-worker.js",
+    "type": "module"
+  },
+  "action": {
+    "default_popup": "src/popup/popup.html",
+    "default_icon": {
+      "16": "src/icons/icon-gray-16.png",
+      "48": "src/icons/icon-gray-48.png",
+      "128": "src/icons/icon-gray-128.png"
+    }
+  },
+  "options_page": "src/options/options.html",
+  "icons": {
+    "16": "src/icons/icon-blue-16.png",
+    "48": "src/icons/icon-blue-48.png",
+    "128": "src/icons/icon-blue-128.png"
+  }
+}
--- a/extension/package-lock.json
+++ b/extension/package-lock.json
@@ -0,0 +1,550 @@
+{
+  "name": "cookiebridge-extension",
+  "version": "0.1.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "cookiebridge-extension",
+      "version": "0.1.0",
+      "dependencies": {
+        "libsodium-wrappers-sumo": "^0.7.15"
+      },
+      "devDependencies": {
+        "@types/chrome": "^0.0.287",
+        "esbuild": "^0.24.2",
+        "typescript": "^5.9.3"
+      }
+    },
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+      "cpu": [
+        "ppc64"
+      ],
+      "dev": true,
+      "license": "MIT",
+      "optional": true,
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+      ],
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+      }
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+      "license": "ISC"
+    },
+    "node_modules/libsodium-wrappers-sumo": {
+      "version": "0.7.16",
+      "resolved": "https://registry.npmjs.org/libsodium-wrappers-sumo/-/libsodium-wrappers-sumo-0.7.16.tgz",
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+      "license": "ISC",
+      "dependencies": {
+        "libsodium-sumo": "^0.7.16"
+      }
+    },
+    "node_modules/typescript": {
+      "version": "5.9.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
+      "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "tsc": "bin/tsc",
+        "tsserver": "bin/tsserver"
+      },
+      "engines": {
+        "node": ">=14.17"
+      }
+    }
+  }
+}
--- a/extension/package.json
+++ b/extension/package.json
@@ -0,0 +1,19 @@
+{
+  "name": "cookiebridge-extension",
+  "version": "0.1.0",
+  "private": true,
+  "description": "CookieBridge Chrome Extension — cross-device cookie sync with E2E encryption",
+  "scripts": {
+    "build": "node esbuild.config.mjs",
+    "watch": "node esbuild.config.mjs --watch",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "libsodium-wrappers-sumo": "^0.7.15"
+  },
+  "devDependencies": {
+    "@types/chrome": "^0.0.287",
+    "esbuild": "^0.24.2",
+    "typescript": "^5.9.3"
+  }
+}
--- a/extension/src/background/service-worker.ts
+++ b/extension/src/background/service-worker.ts
@@ -0,0 +1,315 @@
+/**
+ * CookieBridge background service worker.
+ * Manages device identity, connection lifecycle, and cookie sync.
+ */
+import {
+  generateKeyPair,
+  deviceIdFromKeys,
+  serializeKeyPair,
+  deserializeKeyPair,
+  type DeviceKeyPair,
+} from "../lib/crypto";
+import { getState, setState, type PeerDevice } from "../lib/storage";
+import { ConnectionManager, type ConnectionStatus } from "../lib/connection";
+import { ApiClient } from "../lib/api-client";
+import { SyncEngine } from "../lib/sync";
+import { setIconState, clearSyncBadge } from "../lib/badge";
+import { MESSAGE_TYPES, POLL_INTERVAL_MS, type Envelope } from "../lib/protocol";
+
+let connection: ConnectionManager | null = null;
+let syncEngine: SyncEngine | null = null;
+let api: ApiClient | null = null;
+let pollAlarmName = "cookiebridge-poll";
+
+// --- Initialization ---
+
+async function initialize() {
+  const state = await getState();
+
+  if (!state.keys || !state.apiToken) {
+    await setIconState("not_logged_in");
+    return;
+  }
+
+  const keys = deserializeKeyPair(state.keys);
+  api = new ApiClient(state.serverUrl, state.apiToken);
+
+  connection = new ConnectionManager(state.serverUrl, state.apiToken, keys, {
+    onMessage: (envelope) => handleIncomingMessage(envelope, state.peers),
+    onStatusChange: handleStatusChange,
+  });
+
+  syncEngine = new SyncEngine(keys, connection, api);
+  syncEngine.start();
+
+  if (state.connectionMode === "polling") {
+    startPolling(state.pollIntervalSec);
+  } else {
+    connection.connect();
+  }
+}
+
+function handleStatusChange(status: ConnectionStatus) {
+  switch (status) {
+    case "connected":
+      setIconState("connected");
+      break;
+    case "disconnected":
+    case "connecting":
+      setIconState("not_logged_in");
+      break;
+    case "error":
+      setIconState("error");
+      break;
+  }
+}
+
+async function handleIncomingMessage(envelope: Envelope, peers: PeerDevice[]) {
+  if (
+    envelope.type === MESSAGE_TYPES.COOKIE_SYNC ||
+    envelope.type === MESSAGE_TYPES.COOKIE_DELETE
+  ) {
+    if (!syncEngine) return;
+    await syncEngine.handleIncomingEnvelope(envelope, peers);
+    await setIconState("syncing", 1);
+    clearSyncBadge();
+  }
+}
+
+function startPolling(intervalSec: number) {
+  chrome.alarms.create(pollAlarmName, {
+    periodInMinutes: Math.max(intervalSec / 60, 1 / 60),
+  });
+}
+
+function stopPolling() {
+  chrome.alarms.clear(pollAlarmName);
+}
+
+// --- Alarm handler for HTTP polling ---
+
+chrome.alarms.onAlarm.addListener(async (alarm) => {
+  if (alarm.name !== pollAlarmName) return;
+  if (!api) return;
+
+  const state = await getState();
+  if (!state.lastSyncAt) return;
+
+  try {
+    const updates = await api.pullUpdates(state.lastSyncAt);
+    if (updates.length > 0) {
+      await setState({ lastSyncAt: new Date().toISOString() });
+      await setIconState("syncing", updates.length);
+      clearSyncBadge();
+    }
+  } catch {
+    // Polling failure — will retry on next alarm
+  }
+});
+
+// --- Message handling from popup/options ---
+
+export interface ExtensionMessage {
+  type: string;
+  payload?: unknown;
+}
+
+chrome.runtime.onMessage.addListener(
+  (message: ExtensionMessage, _sender, sendResponse) => {
+    handleMessage(message).then(sendResponse).catch((err) => {
+      sendResponse({ error: err.message });
+    });
+    return true; // async response
+  },
+);
+
+async function handleMessage(msg: ExtensionMessage): Promise<unknown> {
+  switch (msg.type) {
+    case "GET_STATUS":
+      return getStatus();
+
+    case "REGISTER_DEVICE":
+      return registerDevice(msg.payload as { name: string });
+
+    case "INITIATE_PAIRING":
+      return initiatePairing();
+
+    case "ACCEPT_PAIRING":
+      return acceptPairing(msg.payload as { code: string });
+
+    case "SYNC_CURRENT_TAB":
+      if (syncEngine) await syncEngine.syncCurrentTab();
+      return { ok: true };
+
+    case "SYNC_DOMAIN":
+      if (syncEngine) {
+        await syncEngine.syncDomain(
+          (msg.payload as { domain: string }).domain,
+        );
+      }
+      return { ok: true };
+
+    case "ADD_WHITELIST": {
+      const state = await getState();
+      const domain = (msg.payload as { domain: string }).domain;
+      if (!state.whitelist.includes(domain)) {
+        await setState({ whitelist: [...state.whitelist, domain] });
+      }
+      return { ok: true };
+    }
+
+    case "DISCONNECT":
+      connection?.disconnect();
+      stopPolling();
+      return { ok: true };
+
+    case "RECONNECT":
+      await initialize();
+      return { ok: true };
+
+    case "EXPORT_KEYS": {
+      const state = await getState();
+      return { keys: state.keys };
+    }
+
+    case "IMPORT_KEYS": {
+      const keys = msg.payload as {
+        signPub: string;
+        signSec: string;
+        encPub: string;
+        encSec: string;
+      };
+      const kp = deserializeKeyPair(keys);
+      await setState({
+        keys,
+        deviceId: deviceIdFromKeys(kp),
+      });
+      await initialize();
+      return { ok: true };
+    }
+
+    case "LOGOUT":
+      connection?.disconnect();
+      syncEngine?.stop();
+      stopPolling();
+      await setState({
+        keys: null,
+        deviceId: null,
+        deviceName: null,
+        apiToken: null,
+        peers: [],
+        syncCount: 0,
+        lastSyncAt: null,
+        lamportClock: 0,
+      });
+      await setIconState("not_logged_in");
+      return { ok: true };
+
+    default:
+      throw new Error(`Unknown message type: ${msg.type}`);
+  }
+}
+
+async function getStatus(): Promise<{
+  loggedIn: boolean;
+  deviceId: string | null;
+  deviceName: string | null;
+  connectionStatus: ConnectionStatus;
+  peerCount: number;
+  syncCount: number;
+  lastSyncAt: string | null;
+  cookieCount: number;
+}> {
+  const state = await getState();
+
+  // Count tracked cookies
+  let cookieCount = 0;
+  if (state.whitelist.length > 0) {
+    for (const domain of state.whitelist) {
+      const cookies = await chrome.cookies.getAll({ domain });
+      cookieCount += cookies.length;
+    }
+  }
+
+  return {
+    loggedIn: !!state.apiToken,
+    deviceId: state.deviceId,
+    deviceName: state.deviceName,
+    connectionStatus: connection?.status ?? "disconnected",
+    peerCount: state.peers.length,
+    syncCount: state.syncCount,
+    lastSyncAt: state.lastSyncAt,
+    cookieCount,
+  };
+}
+
+async function registerDevice(params: { name: string }) {
+  const keys = await generateKeyPair();
+  const serialized = serializeKeyPair(keys);
+  const deviceId = deviceIdFromKeys(keys);
+
+  const state = await getState();
+  const client = new ApiClient(state.serverUrl);
+  const device = await client.registerDevice({
+    deviceId,
+    name: params.name,
+    platform: "chrome-extension",
+    encPub: serialized.encPub,
+  });
+
+  await setState({
+    keys: serialized,
+    deviceId,
+    deviceName: params.name,
+    apiToken: device.token,
+  });
+
+  await initialize();
+  return { deviceId, name: params.name };
+}
+
+async function initiatePairing() {
+  const state = await getState();
+  if (!state.keys || !api) throw new Error("Not registered");
+
+  const result = await api.initiatePairing(
+    state.deviceId!,
+    state.keys.encPub,
+  );
+  return { pairingCode: result.pairingCode };
+}
+
+async function acceptPairing(params: { code: string }) {
+  const state = await getState();
+  if (!state.keys || !api) throw new Error("Not registered");
+
+  const result = await api.acceptPairing(
+    state.deviceId!,
+    state.keys.encPub,
+    params.code,
+  );
+
+  const peer: PeerDevice = {
+    deviceId: result.peerDeviceId,
+    name: "Paired Device",
+    platform: "unknown",
+    encPub: result.peerX25519PubKey,
+    pairedAt: new Date().toISOString(),
+  };
+
+  await setState({ peers: [...state.peers, peer] });
+  return { peerId: result.peerDeviceId };
+}
+
+// --- Start on install/startup ---
+
+chrome.runtime.onInstalled.addListener(() => {
+  initialize();
+});
+
+chrome.runtime.onStartup.addListener(() => {
+  initialize();
+});
+
+// Initialize immediately for service worker restart
+initialize();
--- a/extension/src/icons/generate-icons.html
+++ b/extension/src/icons/generate-icons.html
@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<html>
+<head><title>Generate CookieBridge Icons</title></head>
+<body>
+<script>
+// Run this in a browser to generate icon PNGs, or use the canvas-based approach in service worker
+const sizes = [16, 48, 128];
+const colors = {
+  gray: '#9CA3AF',
+  blue: '#3B82F6',
+  green: '#22C55E',
+  red: '#EF4444',
+};
+
+for (const [colorName, color] of Object.entries(colors)) {
+  for (const size of sizes) {
+    const canvas = document.createElement('canvas');
+    canvas.width = size;
+    canvas.height = size;
+    const ctx = canvas.getContext('2d');
+
+    // Background circle
+    ctx.beginPath();
+    ctx.arc(size / 2, size / 2, size / 2 - 1, 0, Math.PI * 2);
+    ctx.fillStyle = color;
+    ctx.fill();
+
+    // Cookie icon (simplified)
+    ctx.fillStyle = '#FFFFFF';
+    ctx.font = `bold ${size * 0.5}px sans-serif`;
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'middle';
+    ctx.fillText('C', size / 2, size / 2);
+
+    // Download
+    const link = document.createElement('a');
+    link.download = `icon-${colorName}-${size}.png`;
+    link.href = canvas.toDataURL('image/png');
+    link.click();
+  }
+}
+document.body.textContent = 'Icons generated! Check downloads.';
+</script>
+</body>
+</html>
--- a/extension/src/icons/icon-blue-128.png
+++ b/extension/src/icons/icon-blue-128.png
--- a/extension/src/icons/icon-blue-16.png
+++ b/extension/src/icons/icon-blue-16.png
--- a/extension/src/icons/icon-blue-48.png
+++ b/extension/src/icons/icon-blue-48.png
--- a/extension/src/icons/icon-gray-128.png
+++ b/extension/src/icons/icon-gray-128.png
--- a/extension/src/icons/icon-gray-16.png
+++ b/extension/src/icons/icon-gray-16.png
--- a/extension/src/icons/icon-gray-48.png
+++ b/extension/src/icons/icon-gray-48.png
--- a/extension/src/icons/icon-green-128.png
+++ b/extension/src/icons/icon-green-128.png
--- a/extension/src/icons/icon-green-16.png
+++ b/extension/src/icons/icon-green-16.png
--- a/extension/src/icons/icon-green-48.png
+++ b/extension/src/icons/icon-green-48.png
--- a/extension/src/icons/icon-red-128.png
+++ b/extension/src/icons/icon-red-128.png
--- a/extension/src/icons/icon-red-16.png
+++ b/extension/src/icons/icon-red-16.png
--- a/extension/src/icons/icon-red-48.png
+++ b/extension/src/icons/icon-red-48.png
--- a/extension/src/lib/api-client.ts
+++ b/extension/src/lib/api-client.ts
@@ -0,0 +1,119 @@
+/**
+ * HTTP client for the CookieBridge relay server REST API.
+ */
+import type {
+  DeviceRegisterRequest,
+  DeviceInfo,
+  PairingResult,
+  EncryptedCookieBlob,
+} from "./protocol";
+
+export class ApiClient {
+  constructor(
+    private baseUrl: string,
+    private token: string | null = null,
+  ) {}
+
+  setToken(token: string) {
+    this.token = token;
+  }
+
+  setBaseUrl(url: string) {
+    this.baseUrl = url;
+  }
+
+  private async request<T>(
+    method: string,
+    path: string,
+    body?: unknown,
+  ): Promise<T> {
+    const headers: Record<string, string> = {
+      "Content-Type": "application/json",
+    };
+    if (this.token) {
+      headers["Authorization"] = `Bearer ${this.token}`;
+    }
+    const res = await fetch(`${this.baseUrl}${path}`, {
+      method,
+      headers,
+      body: body ? JSON.stringify(body) : undefined,
+    });
+    if (!res.ok) {
+      const text = await res.text().catch(() => "");
+      throw new Error(`API ${method} ${path}: ${res.status} ${text}`);
+    }
+    return res.json();
+  }
+
+  // --- Device Registration ---
+
+  async registerDevice(req: DeviceRegisterRequest): Promise<DeviceInfo> {
+    return this.request("POST", "/api/devices/register", req);
+  }
+
+  // --- Pairing ---
+
+  async initiatePairing(
+    deviceId: string,
+    x25519PubKey: string,
+  ): Promise<{ pairingCode: string }> {
+    return this.request("POST", "/api/pair", { deviceId, x25519PubKey });
+  }
+
+  async acceptPairing(
+    deviceId: string,
+    x25519PubKey: string,
+    pairingCode: string,
+  ): Promise<PairingResult> {
+    return this.request("POST", "/api/pair/accept", {
+      deviceId,
+      x25519PubKey,
+      pairingCode,
+    });
+  }
+
+  // --- Cookie Storage (HTTP polling) ---
+
+  async pushCookies(
+    blobs: Array<{
+      domain: string;
+      cookieName: string;
+      path: string;
+      nonce: string;
+      ciphertext: string;
+      lamportTs: number;
+    }>,
+  ): Promise<void> {
+    await this.request("POST", "/api/cookies", { cookies: blobs });
+  }
+
+  async pullCookies(domain?: string): Promise<EncryptedCookieBlob[]> {
+    const params = domain ? `?domain=${encodeURIComponent(domain)}` : "";
+    return this.request("GET", `/api/cookies${params}`);
+  }
+
+  async pullUpdates(since: string): Promise<EncryptedCookieBlob[]> {
+    return this.request(
+      "GET",
+      `/api/cookies/updates?since=${encodeURIComponent(since)}`,
+    );
+  }
+
+  async deleteCookie(
+    domain: string,
+    cookieName: string,
+    path: string,
+  ): Promise<void> {
+    await this.request("DELETE", "/api/cookies", {
+      domain,
+      cookieName,
+      path,
+    });
+  }
+
+  // --- Health ---
+
+  async health(): Promise<{ status: string; connections: number }> {
+    return this.request("GET", "/health");
+  }
+}
--- a/extension/src/lib/badge.ts
+++ b/extension/src/lib/badge.ts
@@ -0,0 +1,69 @@
+/**
+ * Badge/icon management — updates extension icon color and badge text
+ * based on connection status and sync activity.
+ *
+ * States:
+ *   - gray:  Not logged in / no device identity
+ *   - blue:  Connected, idle
+ *   - green: Syncing (with count badge)
+ *   - red:   Error / disconnected
+ */
+
+type IconColor = "gray" | "blue" | "green" | "red";
+
+function iconPath(color: IconColor, size: number): string {
+  return `src/icons/icon-${color}-${size}.png`;
+}
+
+function iconSet(color: IconColor): Record<string, string> {
+  return {
+    "16": iconPath(color, 16),
+    "48": iconPath(color, 48),
+    "128": iconPath(color, 128),
+  };
+}
+
+export async function setIconState(
+  state: "not_logged_in" | "connected" | "syncing" | "error",
+  syncCount?: number,
+) {
+  switch (state) {
+    case "not_logged_in":
+      await chrome.action.setIcon({ path: iconSet("gray") });
+      await chrome.action.setBadgeText({ text: "" });
+      break;
+
+    case "connected":
+      await chrome.action.setIcon({ path: iconSet("blue") });
+      await chrome.action.setBadgeText({ text: "" });
+      break;
+
+    case "syncing":
+      await chrome.action.setIcon({ path: iconSet("green") });
+      if (syncCount && syncCount > 0) {
+        await chrome.action.setBadgeText({
+          text: syncCount > 99 ? "99+" : String(syncCount),
+        });
+        await chrome.action.setBadgeBackgroundColor({ color: "#22C55E" });
+      }
+      break;
+
+    case "error":
+      await chrome.action.setIcon({ path: iconSet("red") });
+      await chrome.action.setBadgeText({ text: "!" });
+      await chrome.action.setBadgeBackgroundColor({ color: "#EF4444" });
+      break;
+  }
+}
+
+/** Clear the sync badge after a delay. */
+export function clearSyncBadge(delayMs = 3000) {
+  setTimeout(async () => {
+    const state = await chrome.storage.local.get(["apiToken"]);
+    if (state.apiToken) {
+      await setIconState("connected");
+    } else {
+      await setIconState("not_logged_in");
+    }
+  }, delayMs);
+}
--- a/extension/src/lib/connection.ts
+++ b/extension/src/lib/connection.ts
@@ -0,0 +1,168 @@
+/**
+ * Connection manager — handles WebSocket and HTTP polling connections to the relay server.
+ */
+import { toHex } from "./hex";
+import type { DeviceKeyPair } from "./crypto";
+import { deviceIdFromKeys, sign } from "./crypto";
+import {
+  MESSAGE_TYPES,
+  PING_INTERVAL_MS,
+  PONG_TIMEOUT_MS,
+  type Envelope,
+} from "./protocol";
+
+export type ConnectionStatus = "disconnected" | "connecting" | "connected" | "error";
+
+export interface ConnectionEvents {
+  onMessage: (envelope: Envelope) => void;
+  onStatusChange: (status: ConnectionStatus) => void;
+}
+
+export class ConnectionManager {
+  private ws: WebSocket | null = null;
+  private pingTimer: ReturnType<typeof setInterval> | null = null;
+  private pongTimer: ReturnType<typeof setTimeout> | null = null;
+  private reconnectTimer: ReturnType<typeof setTimeout> | null = null;
+  private reconnectDelay = 1000;
+  private _status: ConnectionStatus = "disconnected";
+  private serverUrl: string;
+  private token: string;
+  private keys: DeviceKeyPair;
+  private events: ConnectionEvents;
+
+  constructor(
+    serverUrl: string,
+    token: string,
+    keys: DeviceKeyPair,
+    events: ConnectionEvents,
+  ) {
+    this.serverUrl = serverUrl;
+    this.token = token;
+    this.keys = keys;
+    this.events = events;
+  }
+
+  get status(): ConnectionStatus {
+    return this._status;
+  }
+
+  private setStatus(s: ConnectionStatus) {
+    this._status = s;
+    this.events.onStatusChange(s);
+  }
+
+  /** Connect via WebSocket. */
+  connect() {
+    if (this.ws) this.disconnect();
+
+    this.setStatus("connecting");
+    const wsUrl = this.serverUrl
+      .replace(/^http/, "ws")
+      .replace(/\/$/, "");
+    this.ws = new WebSocket(`${wsUrl}/ws?token=${encodeURIComponent(this.token)}`);
+
+    this.ws.onopen = () => {
+      this.setStatus("connected");
+      this.reconnectDelay = 1000;
+      this.startPing();
+    };
+
+    this.ws.onmessage = (event) => {
+      try {
+        const data = JSON.parse(event.data as string);
+        if (data.type === MESSAGE_TYPES.PONG) {
+          this.handlePong();
+          return;
+        }
+        if (data.type === MESSAGE_TYPES.PING) {
+          this.sendRaw({ type: MESSAGE_TYPES.PONG });
+          return;
+        }
+        this.events.onMessage(data as Envelope);
+      } catch {
+        // Ignore malformed messages
+      }
+    };
+
+    this.ws.onclose = () => {
+      this.cleanup();
+      this.setStatus("disconnected");
+      this.scheduleReconnect();
+    };
+
+    this.ws.onerror = () => {
+      this.cleanup();
+      this.setStatus("error");
+      this.scheduleReconnect();
+    };
+  }
+
+  disconnect() {
+    if (this.reconnectTimer) {
+      clearTimeout(this.reconnectTimer);
+      this.reconnectTimer = null;
+    }
+    this.cleanup();
+    if (this.ws) {
+      this.ws.close();
+      this.ws = null;
+    }
+    this.setStatus("disconnected");
+  }
+
+  /** Send an envelope over WebSocket. */
+  send(envelope: Envelope) {
+    if (this.ws?.readyState === WebSocket.OPEN) {
+      this.ws.send(JSON.stringify(envelope));
+    }
+  }
+
+  private sendRaw(data: unknown) {
+    if (this.ws?.readyState === WebSocket.OPEN) {
+      this.ws.send(JSON.stringify(data));
+    }
+  }
+
+  private startPing() {
+    this.stopPing();
+    this.pingTimer = setInterval(() => {
+      this.sendRaw({ type: MESSAGE_TYPES.PING });
+      this.pongTimer = setTimeout(() => {
+        // No pong received, connection is dead
+        this.ws?.close();
+      }, PONG_TIMEOUT_MS);
+    }, PING_INTERVAL_MS);
+  }
+
+  private stopPing() {
+    if (this.pingTimer) {
+      clearInterval(this.pingTimer);
+      this.pingTimer = null;
+    }
+    if (this.pongTimer) {
+      clearTimeout(this.pongTimer);
+      this.pongTimer = null;
+    }
+  }
+
+  private handlePong() {
+    if (this.pongTimer) {
+      clearTimeout(this.pongTimer);
+      this.pongTimer = null;
+    }
+  }
+
+  private cleanup() {
+    this.stopPing();
+  }
+
+  private scheduleReconnect() {
+    if (this.reconnectTimer) return;
+    this.reconnectTimer = setTimeout(() => {
+      this.reconnectTimer = null;
+      this.connect();
+    }, this.reconnectDelay);
+    // Exponential backoff, max 30s
+    this.reconnectDelay = Math.min(this.reconnectDelay * 2, 30000);
+  }
+}
--- a/extension/src/lib/crypto.ts
+++ b/extension/src/lib/crypto.ts
@@ -0,0 +1,217 @@
+/**
+ * Browser-compatible crypto module using libsodium-wrappers-sumo.
+ * Mirrors the server's sodium-native API but runs in the browser.
+ */
+import _sodium from "libsodium-wrappers-sumo";
+import { toHex, fromHex, toBase64, fromBase64 } from "./hex";
+
+let sodiumReady: Promise<typeof _sodium> | null = null;
+
+async function getSodium(): Promise<typeof _sodium> {
+  if (!sodiumReady) {
+    sodiumReady = _sodium.ready.then(() => _sodium);
+  }
+  return sodiumReady;
+}
+
+// --- Key Types ---
+
+export interface DeviceKeyPair {
+  signPub: Uint8Array;
+  signSec: Uint8Array;
+  encPub: Uint8Array;
+  encSec: Uint8Array;
+}
+
+export interface SerializedKeyPair {
+  signPub: string; // hex
+  signSec: string; // hex
+  encPub: string; // hex
+  encSec: string; // hex
+}
+
+// --- Key Generation ---
+
+export async function generateKeyPair(): Promise<DeviceKeyPair> {
+  const sodium = await getSodium();
+  const signKp = sodium.crypto_sign_keypair();
+  const encKp = sodium.crypto_box_keypair();
+  return {
+    signPub: signKp.publicKey,
+    signSec: signKp.privateKey,
+    encPub: encKp.publicKey,
+    encSec: encKp.privateKey,
+  };
+}
+
+export function deviceIdFromKeys(keys: DeviceKeyPair): string {
+  return toHex(keys.signPub);
+}
+
+export function serializeKeyPair(keys: DeviceKeyPair): SerializedKeyPair {
+  return {
+    signPub: toHex(keys.signPub),
+    signSec: toHex(keys.signSec),
+    encPub: toHex(keys.encPub),
+    encSec: toHex(keys.encSec),
+  };
+}
+
+export function deserializeKeyPair(data: SerializedKeyPair): DeviceKeyPair {
+  return {
+    signPub: fromHex(data.signPub),
+    signSec: fromHex(data.signSec),
+    encPub: fromHex(data.encPub),
+    encSec: fromHex(data.encSec),
+  };
+}
+
+// --- Encryption ---
+
+export async function deriveSharedKey(
+  ourEncSec: Uint8Array,
+  peerEncPub: Uint8Array,
+): Promise<Uint8Array> {
+  const sodium = await getSodium();
+  const raw = sodium.crypto_scalarmult(ourEncSec, peerEncPub);
+  return sodium.crypto_generichash(32, raw);
+}
+
+export async function encrypt(
+  plaintext: Uint8Array,
+  sharedKey: Uint8Array,
+): Promise<{ nonce: Uint8Array; ciphertext: Uint8Array }> {
+  const sodium = await getSodium();
+  const nonce = sodium.randombytes_buf(
+    sodium.crypto_aead_xchacha20poly1305_ietf_NPUBBYTES,
+  );
+  const ciphertext = sodium.crypto_aead_xchacha20poly1305_ietf_encrypt(
+    plaintext,
+    null, // no additional data
+    null, // unused nsec
+    nonce,
+    sharedKey,
+  );
+  return { nonce, ciphertext };
+}
+
+export async function decrypt(
+  ciphertext: Uint8Array,
+  nonce: Uint8Array,
+  sharedKey: Uint8Array,
+): Promise<Uint8Array> {
+  const sodium = await getSodium();
+  return sodium.crypto_aead_xchacha20poly1305_ietf_decrypt(
+    null, // unused nsec
+    ciphertext,
+    null, // no additional data
+    nonce,
+    sharedKey,
+  );
+}
+
+// --- Signing ---
+
+export async function sign(
+  message: Uint8Array,
+  signSec: Uint8Array,
+): Promise<Uint8Array> {
+  const sodium = await getSodium();
+  return sodium.crypto_sign_detached(message, signSec);
+}
+
+export async function verify(
+  message: Uint8Array,
+  sig: Uint8Array,
+  signPub: Uint8Array,
+): Promise<boolean> {
+  const sodium = await getSodium();
+  try {
+    return sodium.crypto_sign_verify_detached(sig, message, signPub);
+  } catch {
+    return false;
+  }
+}
+
+export function buildSignablePayload(fields: {
+  type: string;
+  from: string;
+  to: string;
+  nonce: string;
+  payload: string;
+  timestamp: string;
+}): Uint8Array {
+  const str =
+    fields.type +
+    fields.from +
+    fields.to +
+    fields.nonce +
+    fields.payload +
+    fields.timestamp;
+  return new TextEncoder().encode(str);
+}
+
+// --- Envelope helpers ---
+
+export async function buildEnvelope(
+  type: string,
+  payload: object,
+  senderKeys: DeviceKeyPair,
+  peerEncPub: Uint8Array,
+  peerDeviceId: string,
+): Promise<{
+  type: string;
+  from: string;
+  to: string;
+  nonce: string;
+  payload: string;
+  timestamp: string;
+  sig: string;
+}> {
+  const fromId = deviceIdFromKeys(senderKeys);
+  const sharedKey = await deriveSharedKey(senderKeys.encSec, peerEncPub);
+  const plaintext = new TextEncoder().encode(JSON.stringify(payload));
+  const { nonce, ciphertext } = await encrypt(plaintext, sharedKey);
+
+  const timestamp = new Date().toISOString();
+  const nonceHex = toHex(nonce);
+  const payloadB64 = toBase64(ciphertext);
+
+  const signable = buildSignablePayload({
+    type,
+    from: fromId,
+    to: peerDeviceId,
+    nonce: nonceHex,
+    payload: payloadB64,
+    timestamp,
+  });
+  const sig = await sign(signable, senderKeys.signSec);
+
+  return {
+    type,
+    from: fromId,
+    to: peerDeviceId,
+    nonce: nonceHex,
+    payload: payloadB64,
+    timestamp,
+    sig: toHex(sig),
+  };
+}
+
+export async function openEnvelope(
+  envelope: {
+    nonce: string;
+    payload: string;
+  },
+  receiverKeys: DeviceKeyPair,
+  peerEncPub: Uint8Array,
+): Promise<unknown> {
+  const sharedKey = await deriveSharedKey(receiverKeys.encSec, peerEncPub);
+  const nonce = fromHex(envelope.nonce);
+  const ciphertext = fromBase64(envelope.payload);
+  const plaintext = await decrypt(ciphertext, nonce, sharedKey);
+  return JSON.parse(new TextDecoder().decode(plaintext));
+}
+
+// Re-export hex utils
+export { toHex, fromHex, toBase64, fromBase64 };
--- a/extension/src/lib/hex.ts
+++ b/extension/src/lib/hex.ts
@@ -0,0 +1,34 @@
+/** Convert Uint8Array to hex string. */
+export function toHex(buf: Uint8Array): string {
+  return Array.from(buf)
+    .map((b) => b.toString(16).padStart(2, "0"))
+    .join("");
+}
+
+/** Convert hex string to Uint8Array. */
+export function fromHex(hex: string): Uint8Array {
+  const bytes = new Uint8Array(hex.length / 2);
+  for (let i = 0; i < hex.length; i += 2) {
+    bytes[i / 2] = parseInt(hex.substring(i, i + 2), 16);
+  }
+  return bytes;
+}
+
+/** Convert Uint8Array to base64 string. */
+export function toBase64(buf: Uint8Array): string {
+  let binary = "";
+  for (let i = 0; i < buf.length; i++) {
+    binary += String.fromCharCode(buf[i]);
+  }
+  return btoa(binary);
+}
+
+/** Convert base64 string to Uint8Array. */
+export function fromBase64(b64: string): Uint8Array {
+  const binary = atob(b64);
+  const bytes = new Uint8Array(binary.length);
+  for (let i = 0; i < binary.length; i++) {
+    bytes[i] = binary.charCodeAt(i);
+  }
+  return bytes;
+}
--- a/extension/src/lib/libsodium-wrappers-sumo.d.ts
+++ b/extension/src/lib/libsodium-wrappers-sumo.d.ts
@@ -0,0 +1,40 @@
+declare module "libsodium-wrappers-sumo" {
+  interface KeyPair {
+    publicKey: Uint8Array;
+    privateKey: Uint8Array;
+    keyType: string;
+  }
+
+  interface Sodium {
+    ready: Promise<void>;
+    crypto_sign_keypair(): KeyPair;
+    crypto_box_keypair(): KeyPair;
+    crypto_scalarmult(privateKey: Uint8Array, publicKey: Uint8Array): Uint8Array;
+    crypto_generichash(hashLength: number, message: Uint8Array): Uint8Array;
+    crypto_aead_xchacha20poly1305_ietf_encrypt(
+      message: Uint8Array,
+      additionalData: Uint8Array | null,
+      nsec: Uint8Array | null,
+      nonce: Uint8Array,
+      key: Uint8Array,
+    ): Uint8Array;
+    crypto_aead_xchacha20poly1305_ietf_decrypt(
+      nsec: Uint8Array | null,
+      ciphertext: Uint8Array,
+      additionalData: Uint8Array | null,
+      nonce: Uint8Array,
+      key: Uint8Array,
+    ): Uint8Array;
+    crypto_aead_xchacha20poly1305_ietf_NPUBBYTES: number;
+    crypto_sign_detached(message: Uint8Array, privateKey: Uint8Array): Uint8Array;
+    crypto_sign_verify_detached(
+      signature: Uint8Array,
+      message: Uint8Array,
+      publicKey: Uint8Array,
+    ): boolean;
+    randombytes_buf(length: number): Uint8Array;
+  }
+
+  const sodium: Sodium;
+  export default sodium;
+}
--- a/extension/src/lib/protocol.ts
+++ b/extension/src/lib/protocol.ts
@@ -0,0 +1,83 @@
+/**
+ * Protocol types — mirrors the server's protocol/spec.ts for use in the extension.
+ */
+
+export const PROTOCOL_VERSION = "2.0.0";
+export const MAX_STORED_COOKIES_PER_DEVICE = 10_000;
+export const PAIRING_CODE_LENGTH = 6;
+export const PAIRING_TTL_MS = 5 * 60 * 1000;
+export const NONCE_BYTES = 24;
+export const PING_INTERVAL_MS = 30_000;
+export const PONG_TIMEOUT_MS = 10_000;
+export const POLL_INTERVAL_MS = 5_000;
+
+export const MESSAGE_TYPES = {
+  COOKIE_SYNC: "cookie_sync",
+  COOKIE_DELETE: "cookie_delete",
+  ACK: "ack",
+  PING: "ping",
+  PONG: "pong",
+  ERROR: "error",
+} as const;
+
+export type MessageType = (typeof MESSAGE_TYPES)[keyof typeof MESSAGE_TYPES];
+
+export interface Envelope {
+  type: MessageType;
+  from: string;
+  to: string;
+  nonce: string;
+  payload: string;
+  timestamp: string;
+  sig: string;
+}
+
+export interface CookieEntry {
+  domain: string;
+  name: string;
+  value: string;
+  path: string;
+  secure: boolean;
+  httpOnly: boolean;
+  sameSite: "strict" | "lax" | "none";
+  expiresAt: string | null;
+}
+
+export interface CookieSyncPayload {
+  action: "set" | "delete";
+  cookies: CookieEntry[];
+  lamportTs: number;
+}
+
+export interface EncryptedCookieBlob {
+  id: string;
+  deviceId: string;
+  domain: string;
+  cookieName: string;
+  path: string;
+  nonce: string;
+  ciphertext: string;
+  lamportTs: number;
+  updatedAt: string;
+}
+
+export interface DeviceRegisterRequest {
+  deviceId: string;
+  name: string;
+  platform: string;
+  encPub: string;
+}
+
+export interface DeviceInfo {
+  deviceId: string;
+  name: string;
+  platform: string;
+  encPub: string;
+  token: string;
+  createdAt: string;
+}
+
+export interface PairingResult {
+  peerDeviceId: string;
+  peerX25519PubKey: string;
+}
--- a/extension/src/lib/storage.ts
+++ b/extension/src/lib/storage.ts
@@ -0,0 +1,109 @@
+/**
+ * Chrome storage wrapper — provides typed access to extension state.
+ */
+import type { SerializedKeyPair } from "./crypto";
+
+export interface PeerDevice {
+  deviceId: string;
+  name: string;
+  platform: string;
+  encPub: string; // hex
+  pairedAt: string;
+}
+
+export interface ExtensionState {
+  // Device identity
+  keys: SerializedKeyPair | null;
+  deviceId: string | null;
+  deviceName: string | null;
+  apiToken: string | null;
+
+  // Server config
+  serverUrl: string;
+  connectionMode: "auto" | "websocket" | "polling";
+  pollIntervalSec: number;
+
+  // Sync settings
+  autoSync: boolean;
+  whitelist: string[]; // domains to sync
+  blacklist: string[]; // domains to never sync (banks, etc.)
+
+  // Paired devices
+  peers: PeerDevice[];
+
+  // Stats
+  syncCount: number;
+  lastSyncAt: string | null;
+
+  // Lamport clock
+  lamportClock: number;
+}
+
+const DEFAULT_STATE: ExtensionState = {
+  keys: null,
+  deviceId: null,
+  deviceName: null,
+  apiToken: null,
+  serverUrl: "http://localhost:3000",
+  connectionMode: "auto",
+  pollIntervalSec: 5,
+  autoSync: true,
+  whitelist: [],
+  blacklist: [
+    "*.bank.*",
+    "*.paypal.com",
+    "*.stripe.com",
+    "accounts.google.com",
+    "login.microsoftonline.com",
+  ],
+  peers: [],
+  syncCount: 0,
+  lastSyncAt: null,
+  lamportClock: 0,
+};
+
+/** Get full extension state, merging defaults. */
+export async function getState(): Promise<ExtensionState> {
+  const data = await chrome.storage.local.get(null);
+  return { ...DEFAULT_STATE, ...data } as ExtensionState;
+}
+
+/** Update specific state fields. */
+export async function setState(
+  partial: Partial<ExtensionState>,
+): Promise<void> {
+  await chrome.storage.local.set(partial);
+}
+
+/** Reset all state to defaults. */
+export async function clearState(): Promise<void> {
+  await chrome.storage.local.clear();
+}
+
+/** Check if a domain matches a pattern (supports leading wildcard *.). */
+function matchDomain(pattern: string, domain: string): boolean {
+  if (pattern.startsWith("*.")) {
+    const suffix = pattern.slice(1); // ".bank." or ".paypal.com"
+    return domain.includes(suffix);
+  }
+  return domain === pattern;
+}
+
+/** Check if a domain is allowed for syncing based on whitelist/blacklist. */
+export function isDomainAllowed(
+  domain: string,
+  whitelist: string[],
+  blacklist: string[],
+): boolean {
+  // Blacklist always wins
+  for (const pattern of blacklist) {
+    if (matchDomain(pattern, domain)) return false;
+  }
+  // If whitelist is empty, allow all (except blacklisted)
+  if (whitelist.length === 0) return true;
+  // If whitelist is non-empty, only allow whitelisted
+  for (const pattern of whitelist) {
+    if (matchDomain(pattern, domain)) return true;
+  }
+  return false;
+}
--- a/extension/src/lib/sync.ts
+++ b/extension/src/lib/sync.ts
@@ -0,0 +1,269 @@
+/**
+ * Cookie sync engine — monitors chrome.cookies, syncs with relay server.
+ */
+import type { CookieEntry, CookieSyncPayload, Envelope } from "./protocol";
+import { MESSAGE_TYPES } from "./protocol";
+import type { DeviceKeyPair } from "./crypto";
+import {
+  deviceIdFromKeys,
+  buildEnvelope,
+  openEnvelope,
+  fromHex,
+} from "./crypto";
+import type { ConnectionManager } from "./connection";
+import type { ApiClient } from "./api-client";
+import { getState, setState, isDomainAllowed, type PeerDevice } from "./storage";
+
+type CookieKey = string;
+
+interface TrackedCookie {
+  entry: CookieEntry;
+  lamportTs: number;
+  sourceDeviceId: string;
+}
+
+function cookieKey(domain: string, name: string, path: string): CookieKey {
+  return `${domain}|${name}|${path}`;
+}
+
+function chromeCookieToEntry(cookie: chrome.cookies.Cookie): CookieEntry {
+  return {
+    domain: cookie.domain,
+    name: cookie.name,
+    value: cookie.value,
+    path: cookie.path,
+    secure: cookie.secure,
+    httpOnly: cookie.httpOnly,
+    sameSite: cookie.sameSite === "strict"
+      ? "strict"
+      : cookie.sameSite === "lax"
+        ? "lax"
+        : "none",
+    expiresAt: cookie.expirationDate
+      ? new Date(cookie.expirationDate * 1000).toISOString()
+      : null,
+  };
+}
+
+export class SyncEngine {
+  private cookies = new Map<CookieKey, TrackedCookie>();
+  private lamportClock = 0;
+  private deviceId: string;
+  private keys: DeviceKeyPair;
+  private connection: ConnectionManager;
+  private api: ApiClient;
+  private suppressLocal = new Set<string>(); // keys to skip on local change (avoid echo)
+
+  constructor(
+    keys: DeviceKeyPair,
+    connection: ConnectionManager,
+    api: ApiClient,
+  ) {
+    this.keys = keys;
+    this.deviceId = deviceIdFromKeys(keys);
+    this.connection = connection;
+    this.api = api;
+  }
+
+  /** Start monitoring cookie changes. */
+  start() {
+    chrome.cookies.onChanged.addListener(this.handleCookieChange);
+  }
+
+  stop() {
+    chrome.cookies.onChanged.removeListener(this.handleCookieChange);
+  }
+
+  /** Handle incoming envelope from WebSocket. */
+  async handleIncomingEnvelope(envelope: Envelope, peers: PeerDevice[]) {
+    const peer = peers.find((p) => p.deviceId === envelope.from);
+    if (!peer) return; // Unknown peer, ignore
+
+    const peerEncPub = fromHex(peer.encPub);
+    const payload = (await openEnvelope(
+      envelope,
+      this.keys,
+      peerEncPub,
+    )) as CookieSyncPayload;
+
+    const applied = this.applyRemote(payload, envelope.from);
+    for (const entry of applied) {
+      await this.applyCookieToBrowser(entry, payload.action);
+    }
+
+    // Update stats
+    const state = await getState();
+    await setState({
+      syncCount: state.syncCount + applied.length,
+      lastSyncAt: new Date().toISOString(),
+      lamportClock: this.lamportClock,
+    });
+  }
+
+  /** Sync a specific domain's cookies to all peers. */
+  async syncDomain(domain: string) {
+    const cookies = await chrome.cookies.getAll({ domain });
+    if (cookies.length === 0) return;
+
+    const entries = cookies.map(chromeCookieToEntry);
+    await this.syncEntriesToPeers(entries, "set");
+  }
+
+  /** Sync the current tab's cookies. */
+  async syncCurrentTab() {
+    const [tab] = await chrome.tabs.query({
+      active: true,
+      currentWindow: true,
+    });
+    if (!tab?.url) return;
+
+    try {
+      const url = new URL(tab.url);
+      await this.syncDomain(url.hostname);
+    } catch {
+      // Invalid URL
+    }
+  }
+
+  get currentLamportTs(): number {
+    return this.lamportClock;
+  }
+
+  private handleCookieChange = async (
+    changeInfo: chrome.cookies.CookieChangeInfo,
+  ) => {
+    const { cookie, removed, cause } = changeInfo;
+
+    // Skip changes caused by us applying remote cookies
+    const key = cookieKey(cookie.domain, cookie.name, cookie.path);
+    if (this.suppressLocal.has(key)) {
+      this.suppressLocal.delete(key);
+      return;
+    }
+
+    // Only sync user-initiated changes (not expired, not evicted)
+    if (cause === "expired" || cause === "evicted") return;
+
+    const state = await getState();
+    if (!state.autoSync) return;
+    if (!isDomainAllowed(cookie.domain, state.whitelist, state.blacklist))
+      return;
+
+    const entry = chromeCookieToEntry(cookie);
+    const action = removed ? "delete" : "set";
+
+    if (!removed) {
+      this.lamportClock++;
+      this.cookies.set(key, {
+        entry,
+        lamportTs: this.lamportClock,
+        sourceDeviceId: this.deviceId,
+      });
+    } else {
+      this.cookies.delete(key);
+    }
+
+    await this.syncEntriesToPeers([entry], action);
+    await setState({ lamportClock: this.lamportClock });
+  };
+
+  private async syncEntriesToPeers(entries: CookieEntry[], action: "set" | "delete") {
+    const state = await getState();
+    this.lamportClock++;
+
+    const payload: CookieSyncPayload = {
+      action,
+      cookies: entries,
+      lamportTs: this.lamportClock,
+    };
+
+    for (const peer of state.peers) {
+      const peerEncPub = fromHex(peer.encPub);
+      const envelope = await buildEnvelope(
+        MESSAGE_TYPES.COOKIE_SYNC,
+        payload,
+        this.keys,
+        peerEncPub,
+        peer.deviceId,
+      );
+      this.connection.send(envelope as unknown as Envelope);
+    }
+  }
+
+  private applyRemote(
+    payload: CookieSyncPayload,
+    sourceDeviceId: string,
+  ): CookieEntry[] {
+    this.lamportClock = Math.max(this.lamportClock, payload.lamportTs) + 1;
+    const applied: CookieEntry[] = [];
+
+    for (const entry of payload.cookies) {
+      const key = cookieKey(entry.domain, entry.name, entry.path);
+      const existing = this.cookies.get(key);
+
+      if (payload.action === "delete") {
+        if (this.shouldApply(existing, payload.lamportTs, sourceDeviceId)) {
+          this.cookies.delete(key);
+          applied.push(entry);
+        }
+        continue;
+      }
+
+      if (this.shouldApply(existing, payload.lamportTs, sourceDeviceId)) {
+        this.cookies.set(key, {
+          entry,
+          lamportTs: payload.lamportTs,
+          sourceDeviceId,
+        });
+        applied.push(entry);
+      }
+    }
+
+    return applied;
+  }
+
+  private shouldApply(
+    existing: TrackedCookie | undefined,
+    incomingTs: number,
+    incomingDeviceId: string,
+  ): boolean {
+    if (!existing) return true;
+    if (incomingTs > existing.lamportTs) return true;
+    if (incomingTs === existing.lamportTs) {
+      return incomingDeviceId > existing.sourceDeviceId;
+    }
+    return false;
+  }
+
+  private async applyCookieToBrowser(entry: CookieEntry, action: "set" | "delete") {
+    const key = cookieKey(entry.domain, entry.name, entry.path);
+    this.suppressLocal.add(key);
+
+    const url = `http${entry.secure ? "s" : ""}://${entry.domain.replace(/^\./, "")}${entry.path}`;
+
+    if (action === "delete") {
+      await chrome.cookies.remove({ url, name: entry.name });
+      return;
+    }
+
+    const details: chrome.cookies.SetDetails = {
+      url,
+      name: entry.name,
+      value: entry.value,
+      path: entry.path,
+      secure: entry.secure,
+      httpOnly: entry.httpOnly,
+      sameSite: entry.sameSite === "strict"
+        ? "strict"
+        : entry.sameSite === "lax"
+          ? "lax"
+          : "no_restriction",
+    };
+
+    if (entry.expiresAt) {
+      details.expirationDate = new Date(entry.expiresAt).getTime() / 1000;
+    }
+
+    await chrome.cookies.set(details);
+  }
+}
--- a/extension/src/options/options.css
+++ b/extension/src/options/options.css
@@ -0,0 +1,305 @@
+* {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+body {
+  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
+  font-size: 14px;
+  color: #1f2937;
+  background: #f9fafb;
+  line-height: 1.5;
+}
+
+.container {
+  max-width: 640px;
+  margin: 0 auto;
+  padding: 32px 24px;
+}
+
+header {
+  margin-bottom: 32px;
+}
+
+header h1 {
+  font-size: 24px;
+  font-weight: 700;
+  color: #111827;
+}
+
+/* Sections */
+.section {
+  background: #ffffff;
+  border: 1px solid #e5e7eb;
+  border-radius: 12px;
+  padding: 20px;
+  margin-bottom: 20px;
+}
+
+.section h2 {
+  font-size: 16px;
+  font-weight: 600;
+  color: #374151;
+  margin-bottom: 16px;
+  padding-bottom: 8px;
+  border-bottom: 1px solid #f3f4f6;
+}
+
+/* Fields */
+.field {
+  margin-bottom: 14px;
+}
+
+.field label {
+  display: block;
+  font-size: 13px;
+  font-weight: 500;
+  color: #374151;
+  margin-bottom: 4px;
+}
+
+.field .value {
+  font-size: 14px;
+  color: #6b7280;
+}
+
+.field .value.mono {
+  font-family: monospace;
+  font-size: 12px;
+  word-break: break-all;
+}
+
+.field input[type="text"],
+.field select {
+  width: 100%;
+  padding: 8px 12px;
+  border: 1px solid #d1d5db;
+  border-radius: 8px;
+  font-size: 14px;
+  outline: none;
+  transition: border-color 0.15s;
+}
+
+.field input[type="text"]:focus,
+.field select:focus {
+  border-color: #3b82f6;
+  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
+}
+
+.field-hint {
+  font-size: 11px;
+  color: #9ca3af;
+  margin-top: 4px;
+}
+
+.field-actions {
+  display: flex;
+  gap: 8px;
+  flex-wrap: wrap;
+}
+
+/* Range */
+.range-group {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+}
+
+.range-group input[type="range"] {
+  flex: 1;
+}
+
+.range-group span {
+  font-size: 13px;
+  font-weight: 600;
+  color: #374151;
+  min-width: 40px;
+}
+
+/* Toggle */
+.toggle-label {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  cursor: pointer;
+}
+
+.toggle-label input[type="checkbox"] {
+  display: none;
+}
+
+.toggle {
+  width: 44px;
+  height: 24px;
+  background: #d1d5db;
+  border-radius: 12px;
+  position: relative;
+  transition: background 0.2s;
+}
+
+.toggle::after {
+  content: "";
+  position: absolute;
+  top: 2px;
+  left: 2px;
+  width: 20px;
+  height: 20px;
+  background: #ffffff;
+  border-radius: 50%;
+  transition: transform 0.2s;
+}
+
+.toggle-label input:checked + .toggle {
+  background: #3b82f6;
+}
+
+.toggle-label input:checked + .toggle::after {
+  transform: translateX(20px);
+}
+
+/* Tags */
+.tag-list {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  margin-bottom: 8px;
+  min-height: 28px;
+}
+
+.tag {
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  padding: 4px 10px;
+  background: #eff6ff;
+  color: #1d4ed8;
+  border-radius: 6px;
+  font-size: 12px;
+  font-weight: 500;
+}
+
+.tag .remove {
+  cursor: pointer;
+  font-size: 14px;
+  color: #93c5fd;
+  margin-left: 2px;
+}
+
+.tag .remove:hover {
+  color: #dc2626;
+}
+
+.add-tag {
+  display: flex;
+  gap: 8px;
+}
+
+.add-tag input {
+  flex: 1;
+  padding: 6px 10px;
+  border: 1px solid #d1d5db;
+  border-radius: 6px;
+  font-size: 13px;
+  outline: none;
+}
+
+.add-tag input:focus {
+  border-color: #3b82f6;
+}
+
+/* Peer List */
+.peer-list {
+  min-height: 40px;
+}
+
+.peer-item {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 10px 0;
+  border-bottom: 1px solid #f3f4f6;
+}
+
+.peer-item:last-child {
+  border-bottom: none;
+}
+
+.peer-info .peer-name {
+  font-weight: 500;
+  font-size: 14px;
+}
+
+.peer-info .peer-id {
+  font-size: 11px;
+  color: #9ca3af;
+  font-family: monospace;
+}
+
+.peer-info .peer-date {
+  font-size: 11px;
+  color: #9ca3af;
+}
+
+.empty-state {
+  color: #9ca3af;
+  font-size: 13px;
+  text-align: center;
+  padding: 12px;
+}
+
+/* Buttons */
+.btn {
+  padding: 8px 16px;
+  border: none;
+  border-radius: 8px;
+  font-size: 13px;
+  font-weight: 500;
+  cursor: pointer;
+  transition: all 0.15s;
+}
+
+.btn-primary {
+  background: #3b82f6;
+  color: #ffffff;
+}
+
+.btn-primary:hover {
+  background: #2563eb;
+}
+
+.btn-secondary {
+  background: #f3f4f6;
+  color: #374151;
+}
+
+.btn-secondary:hover {
+  background: #e5e7eb;
+}
+
+.btn-danger {
+  background: #fef2f2;
+  color: #dc2626;
+}
+
+.btn-danger:hover {
+  background: #fee2e2;
+}
+
+.btn-small {
+  padding: 6px 12px;
+  font-size: 12px;
+}
+
+/* Save Bar */
+.save-bar {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  margin-top: 8px;
+}
+
+.save-status {
+  font-size: 13px;
+  color: #059669;
+}
--- a/extension/src/options/options.html
+++ b/extension/src/options/options.html
@@ -0,0 +1,114 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>CookieBridge Settings</title>
+  <link rel="stylesheet" href="options.css">
+</head>
+<body>
+  <div class="container">
+    <header>
+      <h1>CookieBridge Settings</h1>
+    </header>
+
+    <!-- Account Section -->
+    <section class="section">
+      <h2>Account</h2>
+      <div class="field">
+        <label>Device Name</label>
+        <span id="opt-device-name" class="value">—</span>
+      </div>
+      <div class="field">
+        <label>Device ID</label>
+        <span id="opt-device-id" class="value mono">—</span>
+      </div>
+      <div class="field-actions">
+        <button id="btn-logout" class="btn btn-danger">Log Out</button>
+      </div>
+    </section>
+
+    <!-- Connection Section -->
+    <section class="section">
+      <h2>Connection</h2>
+      <div class="field">
+        <label for="opt-server-url">Server URL</label>
+        <input type="text" id="opt-server-url" placeholder="http://localhost:3000" />
+      </div>
+      <div class="field">
+        <label for="opt-connection-mode">Connection Mode</label>
+        <select id="opt-connection-mode">
+          <option value="auto">Auto (WebSocket preferred)</option>
+          <option value="websocket">WebSocket Only</option>
+          <option value="polling">HTTP Polling</option>
+        </select>
+      </div>
+      <div class="field" id="field-poll-interval">
+        <label for="opt-poll-interval">Poll Interval</label>
+        <div class="range-group">
+          <input type="range" id="opt-poll-interval" min="1" max="60" value="5" />
+          <span id="opt-poll-interval-label">5s</span>
+        </div>
+      </div>
+    </section>
+
+    <!-- Sync Section -->
+    <section class="section">
+      <h2>Sync</h2>
+      <div class="field">
+        <label class="toggle-label">
+          <span>Auto-sync cookies</span>
+          <input type="checkbox" id="opt-auto-sync" />
+          <span class="toggle"></span>
+        </label>
+      </div>
+      <div class="field">
+        <label>Whitelist (sync only these domains)</label>
+        <div class="tag-list" id="whitelist-tags"></div>
+        <div class="add-tag">
+          <input type="text" id="whitelist-input" placeholder="example.com" />
+          <button id="btn-add-whitelist" class="btn btn-small btn-secondary">Add</button>
+        </div>
+        <p class="field-hint">Leave empty to sync all domains (except blacklisted)</p>
+      </div>
+      <div class="field">
+        <label>Blacklist (never sync these domains)</label>
+        <div class="tag-list" id="blacklist-tags"></div>
+        <div class="add-tag">
+          <input type="text" id="blacklist-input" placeholder="*.bank.com" />
+          <button id="btn-add-blacklist" class="btn btn-small btn-secondary">Add</button>
+        </div>
+      </div>
+    </section>
+
+    <!-- Paired Devices Section -->
+    <section class="section">
+      <h2>Paired Devices</h2>
+      <div id="peer-list" class="peer-list">
+        <p class="empty-state">No paired devices yet</p>
+      </div>
+    </section>
+
+    <!-- Security Section -->
+    <section class="section">
+      <h2>Security</h2>
+      <div class="field-actions">
+        <button id="btn-export-keys" class="btn btn-secondary">Export Keys</button>
+        <button id="btn-import-keys" class="btn btn-secondary">Import Keys</button>
+        <input type="file" id="file-import-keys" accept=".json" style="display: none" />
+      </div>
+      <div class="field-actions" style="margin-top: 12px;">
+        <button id="btn-clear-data" class="btn btn-danger">Clear All Local Data</button>
+      </div>
+    </section>
+
+    <!-- Save -->
+    <div class="save-bar">
+      <button id="btn-save" class="btn btn-primary">Save Settings</button>
+      <span id="save-status" class="save-status"></span>
+    </div>
+  </div>
+
+  <script src="../../dist/options/options.js" type="module"></script>
+</body>
+</html>
--- a/extension/src/options/options.ts
+++ b/extension/src/options/options.ts
@@ -0,0 +1,257 @@
+/**
+ * Options page script — manages extension settings.
+ */
+export {};
+
+// --- Messaging helper ---
+
+function sendMessage(type: string, payload?: unknown): Promise<any> {
+  return new Promise((resolve, reject) => {
+    chrome.runtime.sendMessage({ type, payload }, (response) => {
+      if (chrome.runtime.lastError) {
+        reject(new Error(chrome.runtime.lastError.message));
+        return;
+      }
+      if (response?.error) {
+        reject(new Error(response.error));
+        return;
+      }
+      resolve(response);
+    });
+  });
+}
+
+// --- Elements ---
+
+const optDeviceName = document.getElementById("opt-device-name")!;
+const optDeviceId = document.getElementById("opt-device-id")!;
+const btnLogout = document.getElementById("btn-logout") as HTMLButtonElement;
+
+const optServerUrl = document.getElementById("opt-server-url") as HTMLInputElement;
+const optConnectionMode = document.getElementById("opt-connection-mode") as HTMLSelectElement;
+const optPollInterval = document.getElementById("opt-poll-interval") as HTMLInputElement;
+const optPollIntervalLabel = document.getElementById("opt-poll-interval-label")!;
+const fieldPollInterval = document.getElementById("field-poll-interval")!;
+
+const optAutoSync = document.getElementById("opt-auto-sync") as HTMLInputElement;
+const whitelistTags = document.getElementById("whitelist-tags")!;
+const whitelistInput = document.getElementById("whitelist-input") as HTMLInputElement;
+const btnAddWhitelist = document.getElementById("btn-add-whitelist") as HTMLButtonElement;
+const blacklistTags = document.getElementById("blacklist-tags")!;
+const blacklistInput = document.getElementById("blacklist-input") as HTMLInputElement;
+const btnAddBlacklist = document.getElementById("btn-add-blacklist") as HTMLButtonElement;
+
+const peerList = document.getElementById("peer-list")!;
+
+const btnExportKeys = document.getElementById("btn-export-keys") as HTMLButtonElement;
+const btnImportKeys = document.getElementById("btn-import-keys") as HTMLButtonElement;
+const fileImportKeys = document.getElementById("file-import-keys") as HTMLInputElement;
+const btnClearData = document.getElementById("btn-clear-data") as HTMLButtonElement;
+
+const btnSave = document.getElementById("btn-save") as HTMLButtonElement;
+const saveStatus = document.getElementById("save-status")!;
+
+// --- State ---
+
+let whitelist: string[] = [];
+let blacklist: string[] = [];
+
+// --- Load Settings ---
+
+async function loadSettings() {
+  const state = await chrome.storage.local.get(null);
+
+  optDeviceName.textContent = state.deviceName || "—";
+  optDeviceId.textContent = state.deviceId || "—";
+
+  optServerUrl.value = state.serverUrl || "http://localhost:3000";
+  optConnectionMode.value = state.connectionMode || "auto";
+  optPollInterval.value = String(state.pollIntervalSec || 5);
+  optPollIntervalLabel.textContent = `${state.pollIntervalSec || 5}s`;
+  updatePollVisibility();
+
+  optAutoSync.checked = state.autoSync !== false;
+
+  whitelist = state.whitelist || [];
+  blacklist = state.blacklist || [
+    "*.bank.*",
+    "*.paypal.com",
+    "*.stripe.com",
+    "accounts.google.com",
+    "login.microsoftonline.com",
+  ];
+
+  renderTags(whitelistTags, whitelist, "whitelist");
+  renderTags(blacklistTags, blacklist, "blacklist");
+  renderPeers(state.peers || []);
+}
+
+function renderTags(container: HTMLElement, items: string[], listName: string) {
+  container.innerHTML = "";
+  for (const item of items) {
+    const tag = document.createElement("span");
+    tag.className = "tag";
+    tag.innerHTML = `${item}<span class="remove" data-list="${listName}" data-value="${item}">&times;</span>`;
+    container.appendChild(tag);
+  }
+}
+
+function renderPeers(peers: Array<{ deviceId: string; name: string; platform: string; pairedAt: string }>) {
+  if (peers.length === 0) {
+    peerList.innerHTML = '<p class="empty-state">No paired devices yet</p>';
+    return;
+  }
+
+  peerList.innerHTML = "";
+  for (const peer of peers) {
+    const item = document.createElement("div");
+    item.className = "peer-item";
+    item.innerHTML = `
+      <div class="peer-info">
+        <div class="peer-name">${peer.name} (${peer.platform})</div>
+        <div class="peer-id">${peer.deviceId.slice(0, 16)}...</div>
+        <div class="peer-date">Paired: ${new Date(peer.pairedAt).toLocaleDateString()}</div>
+      </div>
+    `;
+    peerList.appendChild(item);
+  }
+}
+
+function updatePollVisibility() {
+  fieldPollInterval.style.display =
+    optConnectionMode.value === "polling" ? "block" : "none";
+}
+
+// --- Event Handlers ---
+
+optConnectionMode.addEventListener("change", updatePollVisibility);
+
+optPollInterval.addEventListener("input", () => {
+  optPollIntervalLabel.textContent = `${optPollInterval.value}s`;
+});
+
+// Tag removal (event delegation)
+document.addEventListener("click", (e) => {
+  const target = e.target as HTMLElement;
+  if (!target.classList.contains("remove")) return;
+
+  const listName = target.dataset.list;
+  const value = target.dataset.value;
+  if (!listName || !value) return;
+
+  if (listName === "whitelist") {
+    whitelist = whitelist.filter((d) => d !== value);
+    renderTags(whitelistTags, whitelist, "whitelist");
+  } else {
+    blacklist = blacklist.filter((d) => d !== value);
+    renderTags(blacklistTags, blacklist, "blacklist");
+  }
+});
+
+btnAddWhitelist.addEventListener("click", () => {
+  const domain = whitelistInput.value.trim();
+  if (domain && !whitelist.includes(domain)) {
+    whitelist.push(domain);
+    renderTags(whitelistTags, whitelist, "whitelist");
+    whitelistInput.value = "";
+  }
+});
+
+btnAddBlacklist.addEventListener("click", () => {
+  const domain = blacklistInput.value.trim();
+  if (domain && !blacklist.includes(domain)) {
+    blacklist.push(domain);
+    renderTags(blacklistTags, blacklist, "blacklist");
+    blacklistInput.value = "";
+  }
+});
+
+// Save
+btnSave.addEventListener("click", async () => {
+  await chrome.storage.local.set({
+    serverUrl: optServerUrl.value.trim(),
+    connectionMode: optConnectionMode.value,
+    pollIntervalSec: parseInt(optPollInterval.value),
+    autoSync: optAutoSync.checked,
+    whitelist,
+    blacklist,
+  });
+
+  // Reconnect with new settings
+  await sendMessage("RECONNECT");
+
+  saveStatus.textContent = "Saved!";
+  setTimeout(() => {
+    saveStatus.textContent = "";
+  }, 2000);
+});
+
+// Logout
+btnLogout.addEventListener("click", async () => {
+  if (!confirm("Are you sure you want to log out? This will remove your device identity.")) {
+    return;
+  }
+  await sendMessage("LOGOUT");
+  window.close();
+});
+
+// Export keys
+btnExportKeys.addEventListener("click", async () => {
+  const result = await sendMessage("EXPORT_KEYS");
+  if (!result?.keys) {
+    alert("No keys to export");
+    return;
+  }
+
+  const blob = new Blob([JSON.stringify(result.keys, null, 2)], {
+    type: "application/json",
+  });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement("a");
+  a.href = url;
+  a.download = "cookiebridge-keys.json";
+  a.click();
+  URL.revokeObjectURL(url);
+});
+
+// Import keys
+btnImportKeys.addEventListener("click", () => {
+  fileImportKeys.click();
+});
+
+fileImportKeys.addEventListener("change", async () => {
+  const file = fileImportKeys.files?.[0];
+  if (!file) return;
+
+  try {
+    const text = await file.text();
+    const keys = JSON.parse(text);
+    if (!keys.signPub || !keys.signSec || !keys.encPub || !keys.encSec) {
+      throw new Error("Invalid key file");
+    }
+    await sendMessage("IMPORT_KEYS", keys);
+    alert("Keys imported successfully. The extension will reconnect.");
+    await loadSettings();
+  } catch (err) {
+    alert(`Failed to import keys: ${(err as Error).message}`);
+  }
+});
+
+// Clear data
+btnClearData.addEventListener("click", async () => {
+  if (
+    !confirm(
+      "This will delete ALL local data including your encryption keys. Are you sure?",
+    )
+  ) {
+    return;
+  }
+  await sendMessage("LOGOUT");
+  await chrome.storage.local.clear();
+  alert("All data cleared.");
+  window.close();
+});
+
+// --- Init ---
+
+loadSettings();
--- a/extension/src/popup/popup.css
+++ b/extension/src/popup/popup.css
@@ -0,0 +1,317 @@
+* {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+body {
+  width: 340px;
+  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
+  font-size: 14px;
+  color: #1f2937;
+  background: #ffffff;
+}
+
+.view {
+  padding: 16px;
+}
+
+/* Login View */
+.logo-section {
+  text-align: center;
+  padding: 24px 0 16px;
+}
+
+.logo {
+  font-size: 48px;
+  margin-bottom: 8px;
+}
+
+h1 {
+  font-size: 20px;
+  font-weight: 600;
+  color: #111827;
+}
+
+.subtitle {
+  font-size: 12px;
+  color: #6b7280;
+  margin-top: 4px;
+}
+
+.login-section {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+input[type="text"] {
+  width: 100%;
+  padding: 10px 12px;
+  border: 1px solid #d1d5db;
+  border-radius: 8px;
+  font-size: 14px;
+  outline: none;
+  transition: border-color 0.15s;
+}
+
+input[type="text"]:focus {
+  border-color: #3b82f6;
+  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
+}
+
+.link {
+  text-align: center;
+  font-size: 12px;
+  color: #3b82f6;
+  text-decoration: none;
+}
+
+.link:hover {
+  text-decoration: underline;
+}
+
+/* Buttons */
+.btn {
+  width: 100%;
+  padding: 10px 16px;
+  border: none;
+  border-radius: 8px;
+  font-size: 14px;
+  font-weight: 500;
+  cursor: pointer;
+  transition: all 0.15s;
+}
+
+.btn:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+.btn-primary {
+  background: #3b82f6;
+  color: #ffffff;
+}
+
+.btn-primary:hover:not(:disabled) {
+  background: #2563eb;
+}
+
+.btn-secondary {
+  background: #f3f4f6;
+  color: #374151;
+}
+
+.btn-secondary:hover:not(:disabled) {
+  background: #e5e7eb;
+}
+
+.btn-ghost {
+  background: transparent;
+  color: #6b7280;
+}
+
+.btn-ghost:hover {
+  color: #374151;
+}
+
+.btn-small {
+  width: auto;
+  padding: 6px 12px;
+  font-size: 12px;
+}
+
+/* Header */
+.header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: 16px;
+}
+
+.user-info {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+}
+
+.avatar {
+  width: 36px;
+  height: 36px;
+  background: #eff6ff;
+  border-radius: 50%;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  font-size: 18px;
+}
+
+.user-details {
+  display: flex;
+  flex-direction: column;
+}
+
+.name {
+  font-weight: 600;
+  font-size: 14px;
+}
+
+.device-id {
+  font-size: 10px;
+  color: #9ca3af;
+  font-family: monospace;
+}
+
+/* Status Badge */
+.status-badge {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  padding: 4px 10px;
+  border-radius: 12px;
+  font-size: 11px;
+  font-weight: 500;
+}
+
+.status-badge .dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+}
+
+.status-badge.connected {
+  background: #ecfdf5;
+  color: #059669;
+}
+
+.status-badge.connected .dot {
+  background: #22c55e;
+}
+
+.status-badge.disconnected {
+  background: #f3f4f6;
+  color: #6b7280;
+}
+
+.status-badge.disconnected .dot {
+  background: #9ca3af;
+}
+
+.status-badge.error {
+  background: #fef2f2;
+  color: #dc2626;
+}
+
+.status-badge.error .dot {
+  background: #ef4444;
+}
+
+.status-badge.connecting {
+  background: #fffbeb;
+  color: #d97706;
+}
+
+.status-badge.connecting .dot {
+  background: #f59e0b;
+}
+
+/* Stats Row */
+.stats-row {
+  display: flex;
+  justify-content: space-around;
+  padding: 12px 0;
+  margin-bottom: 16px;
+  border-top: 1px solid #f3f4f6;
+  border-bottom: 1px solid #f3f4f6;
+}
+
+.stat {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 2px;
+}
+
+.stat-value {
+  font-size: 20px;
+  font-weight: 700;
+  color: #111827;
+}
+
+.stat-label {
+  font-size: 11px;
+  color: #6b7280;
+}
+
+/* Actions */
+.actions {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  margin-bottom: 16px;
+}
+
+/* Pairing Dialog */
+.dialog {
+  background: #f9fafb;
+  border-radius: 10px;
+  padding: 16px;
+  margin-bottom: 16px;
+}
+
+.dialog-title {
+  font-weight: 600;
+  font-size: 13px;
+  margin-bottom: 8px;
+  text-align: center;
+}
+
+.pairing-code {
+  font-size: 32px;
+  font-weight: 700;
+  font-family: monospace;
+  text-align: center;
+  letter-spacing: 8px;
+  color: #3b82f6;
+  padding: 12px;
+}
+
+.pairing-input {
+  text-align: center;
+  font-size: 24px;
+  font-weight: 600;
+  letter-spacing: 6px;
+  font-family: monospace;
+}
+
+.dialog-hint {
+  font-size: 11px;
+  color: #6b7280;
+  text-align: center;
+  margin-top: 8px;
+}
+
+.dialog-actions {
+  display: flex;
+  gap: 8px;
+  margin-top: 12px;
+  justify-content: center;
+}
+
+/* Footer */
+.footer {
+  display: flex;
+  justify-content: space-between;
+  padding-top: 12px;
+  border-top: 1px solid #f3f4f6;
+}
+
+.footer-link {
+  font-size: 12px;
+  color: #6b7280;
+  text-decoration: none;
+}
+
+.footer-link:hover {
+  color: #3b82f6;
+}
--- a/extension/src/popup/popup.html
+++ b/extension/src/popup/popup.html
@@ -0,0 +1,91 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>CookieBridge</title>
+  <link rel="stylesheet" href="popup.css">
+</head>
+<body>
+  <!-- Not Logged In View -->
+  <div id="view-login" class="view" style="display: none;">
+    <div class="logo-section">
+      <div class="logo">🍪</div>
+      <h1>CookieBridge</h1>
+      <p class="subtitle">Cross-device cookie sync</p>
+    </div>
+    <div class="login-section">
+      <input type="text" id="device-name" placeholder="Device name (e.g. MacBook Pro)" />
+      <button id="btn-register" class="btn btn-primary">Register Device</button>
+      <a href="#" id="link-first-use" class="link">First time setup guide</a>
+    </div>
+  </div>
+
+  <!-- Logged In View -->
+  <div id="view-main" class="view" style="display: none;">
+    <!-- Header -->
+    <div class="header">
+      <div class="user-info">
+        <div class="avatar">🍪</div>
+        <div class="user-details">
+          <span id="display-name" class="name"></span>
+          <span id="display-device-id" class="device-id"></span>
+        </div>
+      </div>
+      <div id="connection-status" class="status-badge disconnected">
+        <span class="dot"></span>
+        <span class="label">Disconnected</span>
+      </div>
+    </div>
+
+    <!-- Stats -->
+    <div class="stats-row">
+      <div class="stat">
+        <span id="stat-cookies" class="stat-value">0</span>
+        <span class="stat-label">Cookies</span>
+      </div>
+      <div class="stat">
+        <span id="stat-devices" class="stat-value">0</span>
+        <span class="stat-label">Devices</span>
+      </div>
+      <div class="stat">
+        <span id="stat-syncs" class="stat-value">0</span>
+        <span class="stat-label">Syncs</span>
+      </div>
+    </div>
+
+    <!-- Actions -->
+    <div class="actions">
+      <button id="btn-sync-tab" class="btn btn-primary">Sync Current Site</button>
+      <button id="btn-add-whitelist" class="btn btn-secondary">Add to Whitelist</button>
+      <button id="btn-pair" class="btn btn-secondary">Pair Device</button>
+    </div>
+
+    <!-- Pairing Dialog (hidden by default) -->
+    <div id="pairing-dialog" class="dialog" style="display: none;">
+      <div id="pairing-initiate" style="display: none;">
+        <p class="dialog-title">Your Pairing Code</p>
+        <div id="pairing-code" class="pairing-code"></div>
+        <p class="dialog-hint">Enter this code on the other device within 5 minutes</p>
+      </div>
+      <div id="pairing-accept">
+        <p class="dialog-title">Enter Pairing Code</p>
+        <input type="text" id="input-pairing-code" placeholder="000000" maxlength="6" class="pairing-input" />
+        <div class="dialog-actions">
+          <button id="btn-pairing-accept" class="btn btn-primary btn-small">Pair</button>
+          <button id="btn-pairing-generate" class="btn btn-secondary btn-small">Generate Code</button>
+          <button id="btn-pairing-cancel" class="btn btn-ghost btn-small">Cancel</button>
+        </div>
+      </div>
+    </div>
+
+    <!-- Footer -->
+    <div class="footer">
+      <a href="#" id="btn-settings" class="footer-link">Settings</a>
+      <a href="https://github.com/Rc707Agency/cookiebridge" target="_blank" class="footer-link">Help</a>
+    </div>
+  </div>
+
+  <script src="../../dist/popup/popup.js" type="module"></script>
+</body>
+</html>
--- a/extension/src/popup/popup.ts
+++ b/extension/src/popup/popup.ts
@@ -0,0 +1,206 @@
+/**
+ * Popup script — controls the popup UI interactions.
+ */
+export {};
+
+// --- Elements ---
+
+const viewLogin = document.getElementById("view-login")!;
+const viewMain = document.getElementById("view-main")!;
+
+// Login
+const inputDeviceName = document.getElementById("device-name") as HTMLInputElement;
+const btnRegister = document.getElementById("btn-register") as HTMLButtonElement;
+
+// Main header
+const displayName = document.getElementById("display-name")!;
+const displayDeviceId = document.getElementById("display-device-id")!;
+const connectionStatus = document.getElementById("connection-status")!;
+
+// Stats
+const statCookies = document.getElementById("stat-cookies")!;
+const statDevices = document.getElementById("stat-devices")!;
+const statSyncs = document.getElementById("stat-syncs")!;
+
+// Actions
+const btnSyncTab = document.getElementById("btn-sync-tab") as HTMLButtonElement;
+const btnAddWhitelist = document.getElementById("btn-add-whitelist") as HTMLButtonElement;
+const btnPair = document.getElementById("btn-pair") as HTMLButtonElement;
+const btnSettings = document.getElementById("btn-settings")!;
+
+// Pairing
+const pairingDialog = document.getElementById("pairing-dialog")!;
+const pairingInitiate = document.getElementById("pairing-initiate")!;
+const pairingAccept = document.getElementById("pairing-accept")!;
+const pairingCode = document.getElementById("pairing-code")!;
+const inputPairingCode = document.getElementById("input-pairing-code") as HTMLInputElement;
+const btnPairingAccept = document.getElementById("btn-pairing-accept") as HTMLButtonElement;
+const btnPairingGenerate = document.getElementById("btn-pairing-generate") as HTMLButtonElement;
+const btnPairingCancel = document.getElementById("btn-pairing-cancel") as HTMLButtonElement;
+
+// --- Messaging helper ---
+
+function sendMessage(type: string, payload?: unknown): Promise<any> {
+  return new Promise((resolve, reject) => {
+    chrome.runtime.sendMessage({ type, payload }, (response) => {
+      if (chrome.runtime.lastError) {
+        reject(new Error(chrome.runtime.lastError.message));
+        return;
+      }
+      if (response?.error) {
+        reject(new Error(response.error));
+        return;
+      }
+      resolve(response);
+    });
+  });
+}
+
+// --- UI Updates ---
+
+function showView(loggedIn: boolean) {
+  viewLogin.style.display = loggedIn ? "none" : "block";
+  viewMain.style.display = loggedIn ? "block" : "none";
+}
+
+function updateConnectionBadge(status: string) {
+  connectionStatus.className = `status-badge ${status}`;
+  const label = connectionStatus.querySelector(".label")!;
+  const labels: Record<string, string> = {
+    connected: "Connected",
+    disconnected: "Disconnected",
+    connecting: "Connecting...",
+    error: "Error",
+  };
+  label.textContent = labels[status] || status;
+}
+
+async function refreshStatus() {
+  try {
+    const status = await sendMessage("GET_STATUS");
+    showView(status.loggedIn);
+
+    if (status.loggedIn) {
+      displayName.textContent = status.deviceName || "My Device";
+      displayDeviceId.textContent = status.deviceId
+        ? status.deviceId.slice(0, 12) + "..."
+        : "";
+      updateConnectionBadge(status.connectionStatus);
+      statCookies.textContent = String(status.cookieCount);
+      statDevices.textContent = String(status.peerCount);
+      statSyncs.textContent = String(status.syncCount);
+    }
+  } catch (err) {
+    console.error("Failed to get status:", err);
+    showView(false);
+  }
+}
+
+// --- Event Handlers ---
+
+btnRegister.addEventListener("click", async () => {
+  const name = inputDeviceName.value.trim();
+  if (!name) {
+    inputDeviceName.focus();
+    return;
+  }
+
+  btnRegister.disabled = true;
+  btnRegister.textContent = "Registering...";
+
+  try {
+    await sendMessage("REGISTER_DEVICE", { name });
+    await refreshStatus();
+  } catch (err) {
+    console.error("Registration failed:", err);
+    btnRegister.textContent = "Registration Failed";
+    setTimeout(() => {
+      btnRegister.textContent = "Register Device";
+      btnRegister.disabled = false;
+    }, 2000);
+  }
+});
+
+btnSyncTab.addEventListener("click", async () => {
+  btnSyncTab.disabled = true;
+  btnSyncTab.textContent = "Syncing...";
+  try {
+    await sendMessage("SYNC_CURRENT_TAB");
+    btnSyncTab.textContent = "Synced!";
+    setTimeout(() => {
+      btnSyncTab.textContent = "Sync Current Site";
+      btnSyncTab.disabled = false;
+    }, 1500);
+  } catch (err) {
+    console.error("Sync failed:", err);
+    btnSyncTab.textContent = "Sync Failed";
+    setTimeout(() => {
+      btnSyncTab.textContent = "Sync Current Site";
+      btnSyncTab.disabled = false;
+    }, 2000);
+  }
+});
+
+btnAddWhitelist.addEventListener("click", async () => {
+  const [tab] = await chrome.tabs.query({ active: true, currentWindow: true });
+  if (!tab?.url) return;
+
+  try {
+    const url = new URL(tab.url);
+    await sendMessage("ADD_WHITELIST", { domain: url.hostname });
+    btnAddWhitelist.textContent = "Added!";
+    setTimeout(() => {
+      btnAddWhitelist.textContent = "Add to Whitelist";
+    }, 1500);
+  } catch (err) {
+    console.error("Failed to add whitelist:", err);
+  }
+});
+
+// Pairing
+btnPair.addEventListener("click", () => {
+  pairingDialog.style.display = "block";
+  pairingInitiate.style.display = "none";
+  pairingAccept.style.display = "block";
+  inputPairingCode.value = "";
+  inputPairingCode.focus();
+});
+
+btnPairingGenerate.addEventListener("click", async () => {
+  try {
+    const result = await sendMessage("INITIATE_PAIRING");
+    pairingAccept.style.display = "none";
+    pairingInitiate.style.display = "block";
+    pairingCode.textContent = result.pairingCode;
+  } catch (err) {
+    console.error("Failed to generate pairing code:", err);
+  }
+});
+
+btnPairingAccept.addEventListener("click", async () => {
+  const code = inputPairingCode.value.trim();
+  if (code.length !== 6) return;
+
+  btnPairingAccept.disabled = true;
+  try {
+    await sendMessage("ACCEPT_PAIRING", { code });
+    pairingDialog.style.display = "none";
+    await refreshStatus();
+  } catch (err) {
+    console.error("Pairing failed:", err);
+    btnPairingAccept.disabled = false;
+  }
+});
+
+btnPairingCancel.addEventListener("click", () => {
+  pairingDialog.style.display = "none";
+});
+
+btnSettings.addEventListener("click", (e) => {
+  e.preventDefault();
+  chrome.runtime.openOptionsPage();
+});
+
+// --- Init ---
+
+refreshStatus();
--- a/extension/tsconfig.json
+++ b/extension/tsconfig.json
@@ -0,0 +1,18 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "outDir": "dist",
+    "rootDir": "src",
+    "declaration": false,
+    "sourceMap": true,
+    "lib": ["ES2022", "DOM"],
+    "types": ["chrome"]
+  },
+  "include": ["src/**/*.ts"]
+}