diff --git a/assets/icon.ico b/assets/icon.ico
new file mode 100644
index 0000000..9c79e33
Binary files /dev/null and b/assets/icon.ico differ
diff --git a/assets/icon.png b/assets/icon.png
new file mode 100644
index 0000000..92886de
Binary files /dev/null and b/assets/icon.png differ
diff --git a/assets/tray.png b/assets/tray.png
new file mode 100644
index 0000000..b27f577
Binary files /dev/null and b/assets/tray.png differ
diff --git a/scripts/make-icon.js b/scripts/make-icon.js
new file mode 100644
index 0000000..b445eda
--- /dev/null
+++ b/scripts/make-icon.js
@@ -0,0 +1,94 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const zlib = require('zlib');
+
+function crc32(buf) {
+  let c = ~0;
+  for (let i = 0; i < buf.length; i += 1) {
+    c ^= buf[i];
+    for (let k = 0; k < 8; k += 1) c = (c >>> 1) ^ (0xedb88320 & -(c & 1));
+  }
+  return ~c >>> 0;
+}
+
+function chunk(type, data) {
+  const body = Buffer.concat([Buffer.from(type), data]);
+  const out = Buffer.alloc(8 + body.length);
+  out.writeUInt32BE(data.length, 0);
+  body.copy(out, 4);
+  out.writeUInt32BE(crc32(body), 8 + data.length);
+  return out;
+}
+
+function png(size) {
+  const raw = Buffer.alloc((size * 4 + 1) * size);
+  for (let y = 0; y < size; y += 1) {
+    const row = y * (size * 4 + 1);
+    raw[row] = 0;
+    for (let x = 0; x < size; x += 1) {
+      const nx = x / (size - 1);
+      const ny = y / (size - 1);
+      const onX = Math.abs(nx - ny) < 0.16 || Math.abs(nx - (1 - ny)) < 0.16;
+      const margin = size * 0.18;
+      const inside = x > margin && y > margin && x < size - margin && y < size - margin;
+      const i = row + 1 + x * 4;
+      if (inside && onX) {
+        raw[i] = 255;
+        raw[i + 1] = 255;
+        raw[i + 2] = 255;
+        raw[i + 3] = 255;
+      } else if (inside) {
+        raw[i] = 32;
+        raw[i + 1] = 122;
+        raw[i + 2] = 214;
+        raw[i + 3] = 255;
+      } else {
+        raw[i + 3] = 0;
+      }
+    }
+  }
+  const ihdr = Buffer.alloc(13);
+  ihdr.writeUInt32BE(size, 0);
+  ihdr.writeUInt32BE(size, 4);
+  ihdr[8] = 8;
+  ihdr[9] = 6;
+  return Buffer.concat([
+    Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]),
+    chunk('IHDR', ihdr),
+    chunk('IDAT', zlib.deflateSync(raw)),
+    chunk('IEND', Buffer.alloc(0)),
+  ]);
+}
+
+function ico(images) {
+  const count = images.length;
+  const header = Buffer.alloc(6 + count * 16);
+  header.writeUInt16LE(0, 0);
+  header.writeUInt16LE(1, 2);
+  header.writeUInt16LE(count, 4);
+  let offset = 6 + count * 16;
+  const parts = [header];
+  images.forEach((image, index) => {
+    const entry = 6 + index * 16;
+    header[entry] = image.size === 256 ? 0 : image.size;
+    header[entry + 1] = image.size === 256 ? 0 : image.size;
+    header.writeUInt16LE(1, entry + 4);
+    header.writeUInt16LE(32, entry + 6);
+    header.writeUInt32LE(image.data.length, entry + 8);
+    header.writeUInt32LE(offset, entry + 12);
+    offset += image.data.length;
+    parts.push(image.data);
+  });
+  return Buffer.concat(parts);
+}
+
+const root = path.join(__dirname, '..', 'assets');
+fs.mkdirSync(root, { recursive: true });
+const sizes = [16, 32, 48, 256];
+const images = sizes.map((size) => ({ size, data: png(size) }));
+fs.writeFileSync(path.join(root, 'tray.png'), images[0].data);
+fs.writeFileSync(path.join(root, 'icon.png'), images[3].data);
+fs.writeFileSync(path.join(root, 'icon.ico'), ico(images));
+console.log('wrote icons', images.map((image) => image.data.length).join(','));
diff --git a/src/main/main.js b/src/main/main.js
new file mode 100644
index 0000000..351b64f
--- /dev/null
+++ b/src/main/main.js
@@ -0,0 +1,420 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const {
+  app,
+  BrowserWindow,
+  Tray,
+  Menu,
+  globalShortcut,
+  ipcMain,
+  nativeImage,
+  screen,
+  clipboard,
+  safeStorage,
+} = require('electron');
+
+const { PROVIDERS } = require('./providers');
+const { createConfigStore, deepMerge } = require('./config');
+const { translate } = require('./engines');
+const { captureForeground, commitPaste } = require('./paste');
+
+const POPUP_WIDTH = 560;
+const POPUP_HEIGHT = 140;
+
+let store = null;
+let tray = null;
+let popup = null;
+let settingsWin = null;
+let quitting = false;
+let activeHotkey = null;
+let targetHwnd = null;
+let suppressBlurUntil = 0;
+const inflight = new Map();
+
+const gotLock = app.requestSingleInstanceLock();
+if (!gotLock) {
+  app.quit();
+} else {
+  app.on('second-instance', () => {
+    showPopup();
+  });
+  app.whenReady().then(start).catch((err) => {
+    console.error('[xtranslate] 启动失败', err && err.message ? err.message : err);
+    app.quit();
+  });
+}
+
+function warn(message) {
+  console.warn('[xtranslate]', message);
+}
+
+function webPrefs() {
+  return {
+    preload: path.join(__dirname, '..', 'preload.js'),
+    contextIsolation: true,
+    nodeIntegration: false,
+    sandbox: true,
+  };
+}
+
+function pagePath(name) {
+  const renderer = path.join(__dirname, '..', 'renderer', name);
+  if (fs.existsSync(renderer)) return renderer;
+  const fixture = path.join(__dirname, '..', '..', 'test', 'fixtures', name);
+  if (fs.existsSync(fixture)) return fixture;
+  return null;
+}
+
+function missingHtml(name) {
+  return `<!doctype html><html><head><meta charset="utf-8"></head>
+<body style="margin:0;background:#1c1c1c;color:#f3f3f3;font:14px/1.5 sans-serif;padding:16px">
+  <div>找不到页面 src/renderer/${name}</div>
+  <div>后端已经启动。前端文件还没放进来，所以先显示这张说明。</div>
+</body></html>`;
+}
+
+async function loadPage(win, name) {
+  const file = pagePath(name);
+  if (!file) {
+    await win.loadURL(`data:text/html;charset=utf-8,${encodeURIComponent(missingHtml(name))}`);
+    return;
+  }
+  try {
+    await win.loadFile(file);
+  } catch (err) {
+    warn(`加载 ${name} 失败：${err && err.message}`);
+    await win.loadURL(`data:text/html;charset=utf-8,${encodeURIComponent(missingHtml(name))}`);
+  }
+}
+
+function trayImage() {
+  const candidates = [
+    path.join(__dirname, '..', '..', 'assets', 'tray.png'),
+    path.join(__dirname, '..', '..', 'assets', 'icon.png'),
+  ];
+  for (const file of candidates) {
+    if (!fs.existsSync(file)) continue;
+    const image = nativeImage.createFromPath(file);
+    if (!image.isEmpty()) return image.resize({ width: 16, height: 16 });
+  }
+  return nativeImage.createFromBuffer(Buffer.from(
+    'iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAA' +
+    'GklEQVQ4T2NkoBAwUqifgYoBAwMDw3+G/wwMDAwA' +
+    'BhgBAe0l3n0AAAAASUVORK5CYII=',
+    'base64',
+  ));
+}
+
+function placePopup() {
+  const cursor = screen.getCursorScreenPoint();
+  const display = screen.getDisplayNearestPoint(cursor);
+  const area = display.workArea;
+  const [width, height] = popup.getSize();
+  const x = Math.round(area.x + (area.width - width) / 2);
+  const y = Math.round(area.y + area.height * 0.28);
+  const maxY = area.y + area.height - height;
+  popup.setPosition(x, Math.min(y, maxY));
+}
+
+function emitShow() {
+  if (!popup || popup.isDestroyed()) return;
+  const payload = { engine: store.get().engine, direction: 'auto' };
+  const send = () => {
+    if (popup && !popup.isDestroyed()) popup.webContents.send('xt:show', payload);
+  };
+  if (popup.webContents.isLoading()) popup.webContents.once('did-finish-load', send);
+  else send();
+}
+
+function showPopup() {
+  if (!popup || popup.isDestroyed()) return;
+  if (popup.isVisible()) {
+    popup.hide();
+    return;
+  }
+  targetHwnd = captureForeground();
+  placePopup();
+  suppressBlurUntil = Date.now() + 300;
+  popup.show();
+  popup.focus();
+  emitShow();
+}
+
+function hidePopup() {
+  if (popup && !popup.isDestroyed() && popup.isVisible()) popup.hide();
+}
+
+function applyHotkey(next) {
+  if (!next || typeof next !== 'string' || !next.trim()) {
+    return { ok: false, message: '热键不能为空' };
+  }
+  if (next === activeHotkey && globalShortcut.isRegistered(next)) return { ok: true };
+  const previous = activeHotkey;
+  if (previous && previous !== next) globalShortcut.unregister(previous);
+  if (globalShortcut.isRegistered(next)) globalShortcut.unregister(next);
+  const ok = globalShortcut.register(next, showPopup);
+  if (!ok) {
+    if (previous && previous !== next) {
+      const back = globalShortcut.register(previous, showPopup);
+      if (!back) warn(`原来的热键「${previous}」也没能重新注册`);
+    }
+    return { ok: false, message: `热键「${next}」注册失败，可能被其他程序占用` };
+  }
+  activeHotkey = next;
+  return { ok: true };
+}
+
+function applyLogin(openAtLogin) {
+  try {
+    app.setLoginItemSettings({ openAtLogin: !!openAtLogin });
+  } catch (err) {
+    warn(`设置开机启动失败：${err && err.message}`);
+  }
+}
+
+function broadcast(pub) {
+  for (const win of BrowserWindow.getAllWindows()) {
+    if (!win.isDestroyed()) win.webContents.send('xt:config', pub);
+  }
+}
+
+function refreshTray() {
+  if (!tray) return;
+  const cfg = store.get();
+  const menu = Menu.buildFromTemplate([
+    { label: '设置', click: () => openSettings() },
+    {
+      label: '开机启动',
+      type: 'checkbox',
+      checked: !!cfg.launchAtLogin,
+      click: (item) => {
+        try {
+          setConfig({ launchAtLogin: item.checked });
+        } catch (err) {
+          warn(err.message);
+          refreshTray();
+        }
+      },
+    },
+    { type: 'separator' },
+    { label: '退出', click: () => app.quit() },
+  ]);
+  tray.setContextMenu(menu);
+}
+
+function setConfig(partial) {
+  const prev = store.get();
+  const merged = deepMerge(prev, partial || {});
+  const hotkeyChanged = merged.hotkey !== prev.hotkey;
+  if (hotkeyChanged) {
+    const registered = applyHotkey(merged.hotkey);
+    if (!registered.ok) throw new Error(registered.message);
+  }
+  let pub;
+  try {
+    pub = store.set(partial || {});
+  } catch (err) {
+    if (hotkeyChanged) applyHotkey(prev.hotkey);
+    throw err;
+  }
+  if (partial && Object.prototype.hasOwnProperty.call(partial, 'launchAtLogin')) {
+    applyLogin(!!store.get().launchAtLogin);
+  }
+  broadcast(pub);
+  refreshTray();
+  return pub;
+}
+
+function openSettings() {
+  if (settingsWin && !settingsWin.isDestroyed()) {
+    settingsWin.show();
+    settingsWin.focus();
+    return;
+  }
+  settingsWin = new BrowserWindow({
+    width: 760,
+    height: 680,
+    show: false,
+    autoHideMenuBar: true,
+    title: 'Xtranslate 设置',
+    webPreferences: webPrefs(),
+  });
+  settingsWin.on('closed', () => {
+    settingsWin = null;
+  });
+  loadPage(settingsWin, 'settings.html')
+    .then(() => {
+      if (settingsWin && !settingsWin.isDestroyed()) settingsWin.show();
+    })
+    .catch((err) => warn(err && err.message));
+}
+
+function createPopup() {
+  popup = new BrowserWindow({
+    width: POPUP_WIDTH,
+    height: POPUP_HEIGHT,
+    frame: false,
+    transparent: true,
+    backgroundColor: '#00000000',
+    alwaysOnTop: true,
+    skipTaskbar: true,
+    show: false,
+    resizable: false,
+    minimizable: false,
+    maximizable: false,
+    fullscreenable: false,
+    webPreferences: webPrefs(),
+  });
+  popup.setAlwaysOnTop(true, 'floating');
+  popup.on('blur', () => {
+    if (Date.now() < suppressBlurUntil) return;
+    hidePopup();
+  });
+  popup.on('close', (event) => {
+    if (!quitting) {
+      event.preventDefault();
+      hidePopup();
+    }
+  });
+  loadPage(popup, 'popup.html').catch((err) => warn(err && err.message));
+}
+
+function createTray() {
+  tray = new Tray(trayImage());
+  tray.setToolTip('Xtranslate');
+  refreshTray();
+}
+
+function registerIpc() {
+  ipcMain.handle('xt:translate', async (event, req) => {
+    const body = req || {};
+    const id = body.id != null ? String(body.id) : `${Date.now()}`;
+    const cfg = store.get();
+    const engine = body.engine || cfg.engine;
+    const ac = new AbortController();
+    inflight.set(id, ac);
+    const started = Date.now();
+    try {
+      const result = await translate({
+        text: body.text,
+        direction: body.direction,
+        engine,
+        signal: ac.signal,
+        config: cfg,
+        onPartial: (text) => {
+          if (!event.sender.isDestroyed()) event.sender.send('xt:partial', { id, text });
+        },
+      });
+      return {
+        id,
+        text: result.text,
+        engine,
+        direction: result.direction,
+        ms: Date.now() - started,
+      };
+    } catch (err) {
+      throw new Error((err && err.message) || '翻译失败');
+    } finally {
+      inflight.delete(id);
+    }
+  });
+
+  ipcMain.handle('xt:cancel', (_event, id) => {
+    const ac = inflight.get(String(id));
+    if (ac) ac.abort();
+  });
+
+  ipcMain.handle('xt:commit', async (_event, text) => {
+    const cfg = store.get();
+    await commitPaste({
+      text: String(text ?? ''),
+      clipboard,
+      hwnd: targetHwnd,
+      restore: cfg.restoreClipboard !== false,
+      hide: async () => hidePopup(),
+    });
+  });
+
+  ipcMain.handle('xt:hide', () => {
+    hidePopup();
+  });
+
+  ipcMain.handle('xt:resize', (_event, height) => {
+    if (!popup || popup.isDestroyed()) return;
+    const next = Math.max(80, Math.min(800, Math.round(Number(height) || POPUP_HEIGHT)));
+    popup.setSize(POPUP_WIDTH, next);
+  });
+
+  ipcMain.handle('xt:getConfig', () => store.getPublic());
+
+  ipcMain.handle('xt:setConfig', (_event, partial) => setConfig(partial || {}));
+
+  ipcMain.handle('xt:getProviders', () => PROVIDERS);
+
+  ipcMain.handle('xt:testEngine', async (_event, partial) => {
+    const cfg = deepMerge(store.get(), partial || {});
+    const started = Date.now();
+    try {
+      const result = await translate({
+        text: '你好',
+        direction: 'zh2en',
+        engine: cfg.engine,
+        config: cfg,
+      });
+      return { ok: true, sample: result.text, ms: Date.now() - started };
+    } catch (err) {
+      return {
+        ok: false,
+        sample: '',
+        ms: Date.now() - started,
+        error: (err && err.message) || '翻译失败',
+      };
+    }
+  });
+
+  ipcMain.handle('xt:openSettings', () => {
+    openSettings();
+  });
+}
+
+async function start() {
+  if (process.platform === 'darwin' && app.dock) app.dock.hide();
+  app.setAppUserModelId('com.xtranslate.app');
+
+  store = createConfigStore({
+    filePath: path.join(app.getPath('userData'), 'config.json'),
+    safeStorage,
+    warn,
+  });
+
+  registerIpc();
+  createTray();
+  createPopup();
+
+  const initial = applyHotkey(store.get().hotkey);
+  if (!initial.ok) warn(initial.message);
+  applyLogin(!!store.get().launchAtLogin);
+
+  console.log('[xtranslate] ready', JSON.stringify({
+    hotkey: store.get().hotkey,
+    registered: !!(activeHotkey && globalShortcut.isRegistered(activeHotkey)),
+  }));
+}
+
+app.on('before-quit', () => {
+  quitting = true;
+});
+
+app.on('will-quit', () => {
+  globalShortcut.unregisterAll();
+  if (tray) {
+    tray.destroy();
+    tray = null;
+  }
+});
+
+app.on('window-all-closed', () => {
+  // 托盘常驻，关窗口不退出。
+});
diff --git a/src/main/paste.js b/src/main/paste.js
new file mode 100644
index 0000000..fc78c96
--- /dev/null
+++ b/src/main/paste.js
@@ -0,0 +1,243 @@
+'use strict';
+
+const INPUT_KEYBOARD = 1;
+const KEYEVENTF_KEYUP = 0x0002;
+const VK_CONTROL = 0x11;
+const VK_V = 0x56;
+const VK_MENU = 0x12;
+const ASFW_ANY = 0xffffffff;
+
+const PASTE_DELAY_MS = 60;
+const RESTORE_DELAY_MS = 400;
+
+function normalizeNewlines(value) {
+  return String(value ?? '').replace(/\r\n/g, '\n');
+}
+
+/** 只有剪贴板里仍是我们刚写进去的文本时才恢复，避免盖掉用户中途复制的内容。 */
+function shouldRestoreClipboard(currentText, writtenText) {
+  return normalizeNewlines(currentText) === normalizeNewlines(writtenText);
+}
+
+function snapshotClipboard(clipboard) {
+  const image = typeof clipboard.readImage === 'function' ? clipboard.readImage() : null;
+  return {
+    text: clipboard.readText(),
+    html: typeof clipboard.readHTML === 'function' ? clipboard.readHTML() : '',
+    rtf: typeof clipboard.readRTF === 'function' ? clipboard.readRTF() : '',
+    image: image && typeof image.isEmpty === 'function' && !image.isEmpty() ? image : null,
+  };
+}
+
+function writeSnapshot(clipboard, snap) {
+  const payload = {};
+  if (snap.text) payload.text = snap.text;
+  if (snap.html) payload.html = snap.html;
+  if (snap.rtf) payload.rtf = snap.rtf;
+  if (snap.image) payload.image = snap.image;
+  if (Object.keys(payload).length === 0) {
+    clipboard.clear();
+    return;
+  }
+  clipboard.write(payload);
+}
+
+let win32 = null;
+
+function loadWin32() {
+  if (win32) return win32;
+  if (process.platform !== 'win32') return null;
+  const koffi = require('koffi');
+  const user32 = koffi.load('user32.dll');
+  const kernel32 = koffi.load('kernel32.dll');
+
+  const KEYBDINPUT = koffi.struct('KEYBDINPUT', {
+    wVk: 'uint16_t',
+    wScan: 'uint16_t',
+    dwFlags: 'uint32_t',
+    time: 'uint32_t',
+    dwExtraInfo: 'uintptr_t',
+  });
+  const MOUSEINPUT = koffi.struct('MOUSEINPUT', {
+    dx: 'long',
+    dy: 'long',
+    mouseData: 'uint32_t',
+    dwFlags: 'uint32_t',
+    time: 'uint32_t',
+    dwExtraInfo: 'uintptr_t',
+  });
+  const HARDWAREINPUT = koffi.struct('HARDWAREINPUT', {
+    uMsg: 'uint32_t',
+    wParamL: 'uint16_t',
+    wParamH: 'uint16_t',
+  });
+  const INPUT = koffi.struct('INPUT', {
+    type: 'uint32_t',
+    u: koffi.union({
+      mi: MOUSEINPUT,
+      ki: KEYBDINPUT,
+      hi: HARDWAREINPUT,
+    }),
+  });
+
+  win32 = {
+    koffi,
+    INPUT,
+    GetForegroundWindow: user32.func('void * __stdcall GetForegroundWindow()'),
+    SetForegroundWindow: user32.func('bool __stdcall SetForegroundWindow(void *hWnd)'),
+    AllowSetForegroundWindow: user32.func('bool __stdcall AllowSetForegroundWindow(uint32_t dwProcessId)'),
+    GetWindowThreadProcessId: user32.func('uint32_t __stdcall GetWindowThreadProcessId(void *hWnd, _Out_ uint32_t *lpdwProcessId)'),
+    AttachThreadInput: user32.func('bool __stdcall AttachThreadInput(uint32_t idAttach, uint32_t idAttachTo, bool fAttach)'),
+    GetCurrentThreadId: kernel32.func('uint32_t __stdcall GetCurrentThreadId()'),
+    SendInput: user32.func('unsigned int __stdcall SendInput(unsigned int cInputs, INPUT *pInputs, int cbSize)'),
+  };
+  return win32;
+}
+
+function captureForeground() {
+  try {
+    const api = loadWin32();
+    if (!api) return null;
+    return api.GetForegroundWindow();
+  } catch (err) {
+    console.warn('[xtranslate] 读取前台窗口失败', err && err.message);
+    return null;
+  }
+}
+
+function keyEvent(vk, down) {
+  return {
+    type: INPUT_KEYBOARD,
+    u: {
+      ki: {
+        wVk: vk,
+        wScan: 0,
+        dwFlags: down ? 0 : KEYEVENTF_KEYUP,
+        time: 0,
+        dwExtraInfo: 0,
+      },
+    },
+  };
+}
+
+function sendInputs(api, events) {
+  return api.SendInput(events.length, events, api.koffi.sizeof(api.INPUT));
+}
+
+function forceForeground(api, hwnd) {
+  if (!hwnd) return false;
+  try {
+    api.AllowSetForegroundWindow(ASFW_ANY);
+  } catch {
+    // 允许失败，后面还有 Alt 键技巧
+  }
+
+  let currentThread = 0;
+  let targetThread = 0;
+  let foregroundThread = 0;
+  try {
+    currentThread = api.GetCurrentThreadId();
+    targetThread = api.GetWindowThreadProcessId(hwnd, [0]) || 0;
+    const foreground = api.GetForegroundWindow();
+    if (foreground) foregroundThread = api.GetWindowThreadProcessId(foreground, [0]) || 0;
+  } catch {
+    // 拿不到线程 id 时仍然尝试 SetForegroundWindow
+  }
+
+  const attached = [];
+  const attach = (from, to) => {
+    if (!from || !to || from === to) return;
+    try {
+      if (api.AttachThreadInput(from, to, true)) attached.push([from, to]);
+    } catch {
+      // 挂不上输入队列就继续走 Alt 键
+    }
+  };
+
+  try {
+    attach(foregroundThread, currentThread);
+    attach(targetThread, currentThread);
+    // 模拟一次 Alt，解开 Windows 的前台锁，否则 SetForegroundWindow 经常被拒绝。
+    sendInputs(api, [keyEvent(VK_MENU, true), keyEvent(VK_MENU, false)]);
+    return !!api.SetForegroundWindow(hwnd);
+  } finally {
+    for (const [from, to] of attached.reverse()) {
+      try {
+        api.AttachThreadInput(from, to, false);
+      } catch {
+        // 解开失败不影响粘贴
+      }
+    }
+  }
+}
+
+function sleep(ms) {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+/**
+ * 备份剪贴板 → 写入译文 → 隐藏浮窗 → 切回目标窗口 → Ctrl+V → 条件恢复。
+ * 非 Windows 只写剪贴板并隐藏。
+ */
+async function commitPaste({ text, clipboard, hide, restore, hwnd, sleepImpl }) {
+  const wait = sleepImpl || sleep;
+  const written = String(text ?? '');
+  const snap = snapshotClipboard(clipboard);
+  clipboard.writeText(written);
+  if (hide) await hide();
+
+  if (process.platform !== 'win32') return;
+
+  let api;
+  try {
+    api = loadWin32();
+  } catch (err) {
+    console.warn('[xtranslate] 无法加载 Win32 粘贴，已只写入剪贴板', err && err.message);
+    return;
+  }
+  if (!api) return;
+
+  try {
+    forceForeground(api, hwnd);
+  } catch (err) {
+    console.warn('[xtranslate] 切回目标窗口失败', err && err.message);
+  }
+
+  await wait(PASTE_DELAY_MS);
+  try {
+    sendInputs(api, [
+      keyEvent(VK_CONTROL, true),
+      keyEvent(VK_V, true),
+      keyEvent(VK_V, false),
+      keyEvent(VK_CONTROL, false),
+    ]);
+  } catch (err) {
+    console.warn('[xtranslate] 发送 Ctrl+V 失败', err && err.message);
+  }
+
+  if (!restore) return;
+  await wait(RESTORE_DELAY_MS);
+  try {
+    if (shouldRestoreClipboard(clipboard.readText(), written)) writeSnapshot(clipboard, snap);
+  } catch (err) {
+    console.warn('[xtranslate] 恢复剪贴板失败', err && err.message);
+  }
+}
+
+function inputStructSize() {
+  const api = loadWin32();
+  if (!api) return null;
+  return api.koffi.sizeof(api.INPUT);
+}
+
+module.exports = {
+  captureForeground,
+  commitPaste,
+  inputStructSize,
+  shouldRestoreClipboard,
+  snapshotClipboard,
+  writeSnapshot,
+  normalizeNewlines,
+  PASTE_DELAY_MS,
+  RESTORE_DELAY_MS,
+};
diff --git a/src/preload.js b/src/preload.js
new file mode 100644
index 0000000..257e44e
--- /dev/null
+++ b/src/preload.js
@@ -0,0 +1,25 @@
+'use strict';
+
+const { contextBridge, ipcRenderer } = require('electron');
+
+function listen(channel, cb) {
+  const listener = (_event, payload) => cb(payload);
+  ipcRenderer.on(channel, listener);
+  return () => ipcRenderer.removeListener(channel, listener);
+}
+
+contextBridge.exposeInMainWorld('xt', {
+  translate: (req) => ipcRenderer.invoke('xt:translate', req),
+  onPartial: (cb) => listen('xt:partial', cb),
+  cancel: (id) => ipcRenderer.invoke('xt:cancel', id),
+  commit: (text) => ipcRenderer.invoke('xt:commit', text),
+  hide: () => ipcRenderer.invoke('xt:hide'),
+  resize: (height) => ipcRenderer.invoke('xt:resize', height),
+  onShow: (cb) => listen('xt:show', cb),
+  getConfig: () => ipcRenderer.invoke('xt:getConfig'),
+  setConfig: (partial) => ipcRenderer.invoke('xt:setConfig', partial),
+  getProviders: () => ipcRenderer.invoke('xt:getProviders'),
+  testEngine: (partial) => ipcRenderer.invoke('xt:testEngine', partial),
+  openSettings: () => ipcRenderer.invoke('xt:openSettings'),
+  onConfigChanged: (cb) => listen('xt:config', cb),
+});
diff --git a/test/fixtures/popup.html b/test/fixtures/popup.html
new file mode 100644
index 0000000..a8d64c5
--- /dev/null
+++ b/test/fixtures/popup.html
@@ -0,0 +1,29 @@
+<!doctype html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <meta http-equiv="Content-Security-Policy" content="default-src 'none'; style-src 'unsafe-inline'; script-src 'unsafe-inline'">
+  <title>Xtranslate</title>
+  <style>
+    html, body { margin: 0; height: 100%; background: transparent; }
+    body { font: 14px/1.4 sans-serif; color: #f5f5f5; }
+    main { margin: 8px; padding: 12px 14px; border-radius: 12px; background: #1f1f1f; }
+    #status { color: #9ad; font-size: 12px; }
+  </style>
+</head>
+<body>
+  <main>
+    <div id="status">后端浮窗（fixture）</div>
+  </main>
+  <script>
+    const status = document.getElementById('status');
+    if (window.xt) {
+      window.xt.onShow((payload) => {
+        status.textContent = '已呼出 ' + payload.engine + ' / ' + payload.direction;
+      });
+    } else {
+      status.textContent = 'preload 没有挂上 window.xt';
+    }
+  </script>
+</body>
+</html>
diff --git a/test/fixtures/settings.html b/test/fixtures/settings.html
new file mode 100644
index 0000000..47f5b5c
--- /dev/null
+++ b/test/fixtures/settings.html
@@ -0,0 +1,35 @@
+<!doctype html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <meta http-equiv="Content-Security-Policy" content="default-src 'none'; style-src 'unsafe-inline'; script-src 'unsafe-inline'">
+  <title>Xtranslate 设置</title>
+  <style>
+    body { margin: 0; padding: 20px; font: 14px/1.5 sans-serif; background: #161616; color: #f3f3f3; }
+    pre { white-space: pre-wrap; color: #cde; }
+    button { margin-right: 8px; }
+  </style>
+</head>
+<body>
+  <h1>Xtranslate 设置（fixture）</h1>
+  <p>这是后端自测页。正式界面在 src/renderer/settings.html。</p>
+  <button id="reload" type="button">读取配置</button>
+  <pre id="out">等待 preload…</pre>
+  <script>
+    const out = document.getElementById('out');
+    async function show() {
+      if (!window.xt) {
+        out.textContent = 'preload 没有挂上 window.xt';
+        return;
+      }
+      const config = await window.xt.getConfig();
+      out.textContent = JSON.stringify(config, null, 2);
+    }
+    document.getElementById('reload').addEventListener('click', () => {
+      show().catch((err) => { out.textContent = err.message; });
+    });
+    if (window.xt) window.xt.onConfigChanged(() => { show(); });
+    show().catch((err) => { out.textContent = err.message; });
+  </script>
+</body>
+</html>
diff --git a/test/paste.test.js b/test/paste.test.js
new file mode 100644
index 0000000..f2e08f3
--- /dev/null
+++ b/test/paste.test.js
@@ -0,0 +1,45 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { shouldRestoreClipboard, snapshotClipboard, writeSnapshot, inputStructSize } = require('../src/main/paste');
+
+test('Win32 INPUT 结构按 64 位对齐是 40 字节', { skip: process.platform !== 'win32' }, () => {
+  assert.equal(inputStructSize(), 40);
+});
+
+test('换行差异不影响“是不是我们写进去的”判断', () => {
+  assert.equal(shouldRestoreClipboard('a\r\nb', 'a\nb'), true);
+  assert.equal(shouldRestoreClipboard('user copied', 'translation'), false);
+});
+
+test('剪贴板快照能带回文本、HTML、RTF 和图片', () => {
+  const image = { isEmpty: () => false, id: 'img' };
+  const written = [];
+  const clipboard = {
+    text: 'old',
+    html: '<b>old</b>',
+    rtf: '{\\rtf old}',
+    image,
+    readText: () => clipboard.text,
+    readHTML: () => clipboard.html,
+    readRTF: () => clipboard.rtf,
+    readImage: () => clipboard.image,
+    writeText: (value) => {
+      clipboard.text = value;
+    },
+    write: (payload) => written.push(payload),
+    clear: () => written.push('clear'),
+  };
+  const snap = snapshotClipboard(clipboard);
+  clipboard.writeText('translated');
+  assert.equal(shouldRestoreClipboard(clipboard.readText(), 'translated'), true);
+  writeSnapshot(clipboard, snap);
+  assert.equal(written[0].text, 'old');
+  assert.equal(written[0].html, '<b>old</b>');
+  assert.equal(written[0].rtf, '{\\rtf old}');
+  assert.equal(written[0].image, image);
+
+  clipboard.readText = () => 'user copied later';
+  assert.equal(shouldRestoreClipboard(clipboard.readText(), 'translated'), false);
+});