diff --git a/renderer/core.js b/renderer/core.js
new file mode 100644
index 0000000..1c177d4
--- /dev/null
+++ b/renderer/core.js
@@ -0,0 +1,454 @@
+// MarkLite — Core Module: state, DOM refs, settings, utilities, init orchestration
+(function () {
+  'use strict';
+
+  // ===== Shared Namespace =====
+  const ML = {};
+  window.MarkLite = ML;
+
+  // ===== DOM Elements =====
+  ML.editor = document.getElementById('editor');
+  ML.preview = document.getElementById('preview');
+  ML.lineNumbers = document.getElementById('line-numbers');
+  ML.welcomeScreen = document.getElementById('welcome-screen');
+  ML.dropOverlay = document.getElementById('drop-overlay');
+  ML.modifiedBanner = document.getElementById('modified-banner');
+  ML.statusText = document.getElementById('status-text');
+  ML.statusCursor = document.getElementById('status-cursor');
+  ML.statusSize = document.getElementById('status-size');
+  ML.statusSizeDivider = document.querySelector('.status-size-divider');
+  ML.resizer = document.getElementById('resizer');
+  ML.editorPanel = document.getElementById('editor-panel');
+  ML.previewPanel = document.getElementById('preview-panel');
+  ML.mainContent = document.getElementById('main-content');
+  ML.contentWrapper = document.getElementById('content-wrapper');
+  ML.tabList = document.getElementById('tab-list');
+
+  // Sidebar
+  ML.sidebar = document.getElementById('sidebar');
+  ML.sidebarTree = document.getElementById('sidebar-tree');
+  ML.btnOpenFolder = document.getElementById('btn-open-folder');
+
+  // Search
+  ML.searchBar = document.getElementById('search-bar');
+  ML.searchInput = document.getElementById('search-input');
+  ML.replaceInput = document.getElementById('replace-input');
+  ML.searchCount = document.getElementById('search-count');
+  ML.replaceRow = document.getElementById('replace-row');
+  ML.btnCase = document.getElementById('btn-case');
+  ML.btnRegex = document.getElementById('btn-regex');
+  ML.btnNext = document.getElementById('btn-next');
+  ML.btnPrev = document.getElementById('btn-prev');
+  ML.btnSearchClose = document.getElementById('btn-search-close');
+  ML.btnReplace = document.getElementById('btn-replace');
+  ML.btnReplaceAll = document.getElementById('btn-replace-all');
+
+  // Buttons
+  ML.btnOpen = document.getElementById('btn-open');
+  ML.btnSave = document.getElementById('btn-save');
+  ML.btnSplit = document.getElementById('btn-split');
+  ML.btnEditor = document.getElementById('btn-editor');
+  ML.btnPreview = document.getElementById('btn-preview');
+  ML.btnWelcomeOpen = document.getElementById('btn-welcome-open');
+  ML.btnWelcomeNew = document.getElementById('btn-welcome-new');
+  ML.btnDark = document.getElementById('btn-dark');
+  ML.btnReload = document.getElementById('btn-reload');
+  ML.btnDismiss = document.getElementById('btn-dismiss');
+  ML.btnNewTab = document.getElementById('btn-new-tab');
+
+  // ===== Shared State =====
+  ML.viewMode = 'split';
+  ML.updateTimer = null;
+  ML.lineCountCache = 0;
+  ML.currentRootPath = null;
+  ML.MAX_FILE_SIZE = 20 * 1024 * 1024;
+
+  // ===== Settings =====
+  ML.loadSettings = function () {
+    try { return JSON.parse(localStorage.getItem('marklite-settings') || '{}'); }
+    catch { return {}; }
+  };
+  ML.saveSetting = function (key, value) {
+    try {
+      const s = ML.loadSettings();
+      s[key] = value;
+      localStorage.setItem('marklite-settings', JSON.stringify(s));
+    } catch { /* ignore */ }
+  };
+
+  // ===== Utilities =====
+  ML.getFileName = function (filePath) {
+    return filePath.split(/[/\\]/).pop();
+  };
+
+  ML.formatBytes = function (bytes) {
+    if (bytes < 1024) return bytes + ' B';
+    if (bytes < 1024 * 1024) return (bytes / 1024).toFixed(1) + ' KB';
+    return (bytes / (1024 * 1024)).toFixed(1) + ' MB';
+  };
+
+  // Character width measurement
+  var _charWidthCanvas = document.createElement('canvas');
+  var _charWidthCtx = _charWidthCanvas.getContext('2d');
+  var _cachedCharWidth = null;
+  ML.getCharWidth = function () {
+    if (_cachedCharWidth !== null) return _cachedCharWidth;
+    var style = getComputedStyle(ML.editor);
+    _charWidthCtx.font = style.fontSize + ' ' + style.fontFamily;
+    _cachedCharWidth = _charWidthCtx.measureText('M').width;
+    return _cachedCharWidth;
+  };
+  new MutationObserver(function () { _cachedCharWidth = null; })
+    .observe(document.documentElement, { attributes: true, attributeFilter: ['class'] });
+
+  // Toast notification
+  ML.showToast = function (message, duration) {
+    duration = duration || 3000;
+    var toast = document.getElementById('toast-notification');
+    if (!toast) {
+      toast = document.createElement('div');
+      toast.id = 'toast-notification';
+      document.getElementById('app').appendChild(toast);
+    }
+    toast.textContent = message;
+    toast.classList.add('show');
+    clearTimeout(toast._timer);
+    toast._timer = setTimeout(function () { toast.classList.remove('show'); }, duration);
+  };
+
+  // ===== Dark Mode =====
+  ML.initDarkMode = function () {
+    var settings = ML.loadSettings();
+    var iconDark = document.getElementById('icon-dark');
+    var iconLight = document.getElementById('icon-light');
+    function apply(isDark) {
+      document.documentElement.classList.toggle('dark', isDark);
+      iconDark.style.display = isDark ? 'none' : '';
+      iconLight.style.display = isDark ? '' : 'none';
+    }
+    var prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
+    apply(settings.darkMode !== undefined ? !!settings.darkMode : prefersDark);
+    ML.btnDark.addEventListener('click', function () {
+      var isDark = !document.documentElement.classList.contains('dark');
+      apply(isDark);
+      ML.saveSetting('darkMode', isDark);
+    });
+  };
+
+  // ===== File Operations =====
+  ML.handleOpenFile = async function () {
+    if (typeof window.electronAPI !== 'undefined') {
+      var result = await window.electronAPI.openFile();
+      if (result && !result.error) {
+        ML.createNewTab(result.filePath, result.content);
+      }
+    } else {
+      var input = document.createElement('input');
+      input.type = 'file';
+      input.accept = '.md,.markdown,.txt';
+      input.multiple = true;
+      input.onchange = function (e) {
+        Array.from(e.target.files).forEach(function (file) {
+          var ext = file.name.substring(file.name.lastIndexOf('.')).toLowerCase();
+          if (!['.md', '.markdown', '.txt'].includes(ext)) return;
+          if (file.size > ML.MAX_FILE_SIZE) {
+            alert('"' + file.name + '" 过大（' + ML.formatBytes(file.size) + '），暂不支持超过 20MB 的文件');
+            return;
+          }
+          var reader = new FileReader();
+          reader.onload = function (ev) { ML.createNewTab(file.name, ev.target.result); };
+          reader.readAsText(file);
+        });
+      };
+      input.click();
+    }
+  };
+
+  ML.handleSave = async function () {
+    var tab = ML.getActiveTab();
+    if (!tab) return;
+    if (typeof window.electronAPI !== 'undefined') {
+      var result = await window.electronAPI.saveFile({ filePath: tab.filePath, content: ML.editor.value });
+      if (result.success) {
+        tab.filePath = result.filePath;
+        tab.content = ML.editor.value;
+        tab.isModified = false;
+        ML.renderTabBar();
+        ML.updateTitle();
+        ML.updateSidebarHighlight();
+        ML.statusText.textContent = '已保存';
+        setTimeout(function () { ML.updateTitle(); }, 2000);
+      }
+    } else {
+      var blob = new Blob([ML.editor.value], { type: 'text/markdown' });
+      var a = document.createElement('a');
+      a.href = URL.createObjectURL(blob);
+      a.download = tab.filePath || 'untitled.md';
+      a.click();
+      setTimeout(function () { URL.revokeObjectURL(a.href); }, 1000);
+      tab.isModified = false;
+      ML.renderTabBar();
+      ML.updateTitle();
+    }
+  };
+
+  ML.handleSaveAs = async function () {
+    var tab = ML.getActiveTab();
+    if (!tab) return;
+    if (typeof window.electronAPI !== 'undefined') {
+      var result = await window.electronAPI.saveFileAs({ content: ML.editor.value });
+      if (result.success) {
+        tab.filePath = result.filePath;
+        tab.content = ML.editor.value;
+        tab.isModified = false;
+        ML.renderTabBar();
+        ML.updateTitle();
+        ML.updateSidebarHighlight();
+        ML.statusText.textContent = '已保存';
+        setTimeout(function () { ML.updateTitle(); }, 2000);
+      }
+    } else {
+      ML.handleSave();
+    }
+  };
+
+  // ===== View Mode =====
+  ML.setViewMode = function (mode) {
+    ML.viewMode = mode;
+    var app = document.getElementById('app');
+    app.classList.remove('mode-editor', 'mode-preview');
+    ML.btnSplit.classList.remove('active');
+    ML.btnEditor.classList.remove('active');
+    ML.btnPreview.classList.remove('active');
+    switch (mode) {
+      case 'split': ML.btnSplit.classList.add('active'); break;
+      case 'editor': ML.btnEditor.classList.add('active'); app.classList.add('mode-editor'); break;
+      case 'preview': ML.btnPreview.classList.add('active'); app.classList.add('mode-preview'); ML.renderMarkdown(ML.editor.value); break;
+    }
+    ML.saveSetting('viewMode', mode);
+  };
+
+  // ===== Resizer =====
+  ML.initResizer = function () {
+    var settings = ML.loadSettings();
+    if (settings.splitRatio) {
+      ML.editorPanel.style.flex = '0 0 ' + settings.splitRatio + '%';
+      ML.previewPanel.style.flex = '0 0 ' + (100 - settings.splitRatio) + '%';
+    }
+    var isResizing = false;
+    ML.resizer.addEventListener('mousedown', function (e) {
+      isResizing = true;
+      ML.resizer.classList.add('active');
+      document.body.style.cursor = 'col-resize';
+      document.body.style.userSelect = 'none';
+      e.preventDefault();
+    });
+    document.addEventListener('mousemove', function (e) {
+      if (!isResizing) return;
+      var rect = ML.contentWrapper.getBoundingClientRect();
+      var pct = Math.max(20, Math.min(80, ((e.clientX - rect.left) / rect.width) * 100));
+      ML.editorPanel.style.flex = '0 0 ' + pct + '%';
+      ML.previewPanel.style.flex = '0 0 ' + (100 - pct) + '%';
+      ML.saveSetting('splitRatio', pct);
+    });
+    document.addEventListener('mouseup', function () {
+      if (isResizing) {
+        isResizing = false;
+        ML.resizer.classList.remove('active');
+        document.body.style.cursor = '';
+        document.body.style.userSelect = '';
+      }
+    });
+  };
+
+  // ===== Drag & Drop =====
+  ML.initDragDrop = function () {
+    var dragCounter = 0;
+    var allowedExts = ['.md', '.markdown', '.txt'];
+    document.addEventListener('dragenter', function (e) { e.preventDefault(); e.stopPropagation(); dragCounter++; ML.dropOverlay.classList.remove('hidden'); });
+    document.addEventListener('dragleave', function (e) { e.preventDefault(); e.stopPropagation(); dragCounter--; if (dragCounter === 0) ML.dropOverlay.classList.add('hidden'); });
+    document.addEventListener('dragover', function (e) { e.preventDefault(); e.stopPropagation(); });
+    document.addEventListener('drop', async function (e) {
+      e.preventDefault(); e.stopPropagation(); dragCounter = 0; ML.dropOverlay.classList.add('hidden');
+      var files = e.dataTransfer.files;
+      var rejected = 0;
+      for (var _i = 0; _i < files.length; _i++) {
+        var file = files[_i];
+        var filePath = file.path;
+        var ext = filePath ? filePath.substring(filePath.lastIndexOf('.')).toLowerCase() : '';
+        if (!allowedExts.includes(ext)) { rejected++; continue; }
+        if (file.size > ML.MAX_FILE_SIZE) { ML.showToast('"' + file.name + '" 过大（' + ML.formatBytes(file.size) + '），暂不支持超过 20MB 的文件'); continue; }
+        if (filePath && typeof window.electronAPI !== 'undefined') {
+          var result = await window.electronAPI.readFile(filePath);
+          if (result.success) ML.createNewTab(filePath, result.content);
+        } else {
+          var reader = new FileReader();
+          reader.onload = function (ev) { ML.createNewTab(file.name, ev.target.result); };
+          reader.readAsText(file);
+        }
+      }
+      if (rejected > 0) ML.showToast('仅支持 .md / .markdown / .txt 文件，已忽略 ' + rejected + ' 个文件');
+    });
+  };
+
+  // ===== Keyboard Shortcuts =====
+  ML.initKeyboard = function () {
+    document.addEventListener('keydown', function (e) {
+      if (e.ctrlKey && e.key === 'o') { e.preventDefault(); ML.handleOpenFile(); }
+      if (e.ctrlKey && e.key === 's' && !e.shiftKey) { e.preventDefault(); ML.handleSave(); }
+      if (e.ctrlKey && e.shiftKey && e.key === 'S') { e.preventDefault(); ML.handleSaveAs(); }
+      if (e.ctrlKey && e.key === '1') { e.preventDefault(); ML.setViewMode('split'); }
+      if (e.ctrlKey && e.key === '2') { e.preventDefault(); ML.setViewMode('editor'); }
+      if (e.ctrlKey && e.key === '3') { e.preventDefault(); ML.setViewMode('preview'); }
+      if (e.ctrlKey && e.key === 't') { e.preventDefault(); ML.createNewTab(null, ''); }
+      if (e.ctrlKey && e.key === 'w') { e.preventDefault(); if (ML.activeTabId) ML.closeTab(ML.activeTabId); }
+      if (e.ctrlKey && e.key === 'Tab') {
+        e.preventDefault();
+        if (ML.tabs.length > 1) {
+          if (e.shiftKey) {
+            if (ML.mruTabStack.length > 0) {
+              var targetId = ML.mruTabStack.shift();
+              if (ML.tabs.find(function (t) { return t.id === targetId; })) ML.switchToTab(targetId);
+            }
+          } else {
+            var idx = ML.getTabIndex(ML.activeTabId);
+            var next = (idx + 1) % ML.tabs.length;
+            ML.switchToTab(ML.tabs[next].id);
+          }
+        }
+      }
+      if (e.ctrlKey && e.key === 'f') { e.preventDefault(); ML.openSearch(false); }
+      if (e.ctrlKey && e.key === 'h') { e.preventDefault(); ML.openSearch(true); }
+      if (e.key === 'Escape' && !ML.searchBar.classList.contains('hidden')) { e.preventDefault(); ML.closeSearch(); }
+      if (e.key === 'Enter' && document.activeElement === ML.searchInput) { e.preventDefault(); e.shiftKey ? ML.findPrev() : ML.findNext(); }
+      if (e.altKey && e.key === 'c') { e.preventDefault(); ML.toggleSearchOption('case'); }
+      if (e.altKey && e.key === 'r') { e.preventDefault(); ML.toggleSearchOption('regex'); }
+      if (e.ctrlKey && e.shiftKey && e.key === 'H') { e.preventDefault(); ML.replaceAll(); }
+      if (e.ctrlKey && e.shiftKey && e.key === 'G') { e.preventDefault(); ML.replaceCurrent(); }
+    });
+  };
+
+  // ===== Tab Key Support =====
+  ML.initEditorTab = function () {
+    ML.editor.addEventListener('keydown', function (e) {
+      if (e.key === 'Tab') {
+        e.preventDefault();
+        var start = ML.editor.selectionStart;
+        var end = ML.editor.selectionEnd;
+        if (start !== end) {
+          var lines = ML.editor.value.substring(start, end).split('\n');
+          var indented = lines.map(function (line) { return '    ' + line; }).join('\n');
+          ML.editor.setRangeText(indented, start, end, 'end');
+        } else {
+          ML.editor.setRangeText('    ', start, end, 'end');
+        }
+        ML.scheduleUpdate();
+      }
+    });
+  };
+
+  // ===== External File Modification =====
+  ML.initFileWatch = function () {
+    if (typeof window.electronAPI === 'undefined') return;
+    window.electronAPI.onExternalModification(function (filePath) {
+      var tab = ML.getActiveTab();
+      if (tab && tab.filePath === filePath) ML.modifiedBanner.classList.remove('hidden');
+    });
+    ML.btnReload.addEventListener('click', async function () {
+      var tab = ML.getActiveTab();
+      if (!tab || !tab.filePath) return;
+      var result = await window.electronAPI.reloadFile();
+      if (result.success) {
+        ML.editor.value = result.content;
+        tab.content = result.content;
+        tab.isModified = false;
+        ML.lineCountCache = 0;
+        ML.updateLineNumbers();
+        ML.renderMarkdown(result.content);
+        ML.updateCursorPosition();
+        ML.updateFileSize();
+        ML.cachePreviewPositions();
+        ML.renderTabBar();
+        ML.updateTitle();
+      }
+      ML.modifiedBanner.classList.add('hidden');
+    });
+    ML.btnDismiss.addEventListener('click', function () { ML.modifiedBanner.classList.add('hidden'); });
+  };
+
+  // ===== Unsaved Changes Warning =====
+  ML.initUnsavedWarning = function () {
+    var hasUnsaved = function () { return ML.tabs.some(function (t) { return t.isModified; }); };
+    if (typeof window.electronAPI === 'undefined') {
+      window.addEventListener('beforeunload', function (e) { if (hasUnsaved()) { e.preventDefault(); e.returnValue = ''; } });
+      return;
+    }
+    window.electronAPI.onConfirmClose(function () {
+      if (!hasUnsaved()) { window.electronAPI.forceClose(); return; }
+      var shouldClose = confirm('有文件尚未保存，确定要关闭吗？');
+      if (shouldClose) window.electronAPI.forceClose();
+      else window.electronAPI.cancelClose();
+    });
+  };
+
+  // ===== Event Listeners =====
+  ML.initEventListeners = function () {
+    ML.editor.addEventListener('input', function () {
+      var tab = ML.getActiveTab();
+      if (tab) { tab.isModified = true; tab.content = ML.editor.value; ML.setModified(true); }
+      ML.scheduleUpdate();
+    });
+    ML.editor.addEventListener('scroll', function () {
+      ML.syncScroll();
+      ML.lineNumbers.scrollTop = ML.editor.scrollTop;
+      if (ML.lineCountCache > 2000) ML.renderVirtualLineNumbers(ML.lineCountCache);
+    });
+    ML.editor.addEventListener('click', ML.updateCursorPosition);
+    ML.editor.addEventListener('keyup', ML.updateCursorPosition);
+    ML.editor.addEventListener('select', ML.updateCursorPosition);
+
+    ML.btnOpen.addEventListener('click', ML.handleOpenFile);
+    ML.btnSave.addEventListener('click', ML.handleSave);
+    ML.btnSplit.addEventListener('click', function () { ML.setViewMode('split'); });
+    ML.btnEditor.addEventListener('click', function () { ML.setViewMode('editor'); });
+    ML.btnPreview.addEventListener('click', function () { ML.setViewMode('preview'); });
+    ML.btnNewTab.addEventListener('click', function () { ML.createNewTab(null, ''); });
+    ML.btnWelcomeOpen.addEventListener('click', ML.handleOpenFile);
+    ML.btnWelcomeNew.addEventListener('click', function () { ML.createNewTab(null, ''); });
+
+    if (typeof window.electronAPI !== 'undefined') {
+      window.electronAPI.removeAllListeners('file:openInTab');
+      window.electronAPI.removeAllListeners('menu:save');
+      window.electronAPI.removeAllListeners('menu:saveAs');
+      window.electronAPI.removeAllListeners('menu:viewMode');
+      window.electronAPI.onFileOpenInTab(function (data) { ML.createNewTab(data.filePath, data.content); });
+      window.electronAPI.onMenuSave(function () { ML.handleSave(); });
+      window.electronAPI.onMenuSaveAs(function () { ML.handleSaveAs(); });
+      window.electronAPI.onViewModeChange(function (mode) { ML.setViewMode(mode); });
+    }
+  };
+
+  // ===== Init =====
+  ML.init = function () {
+    ML.initMarked();
+    ML.initDarkMode();
+    ML.initResizer();
+    ML.initDragDrop();
+    ML.initKeyboard();
+    ML.initEditorTab();
+    ML.initPreviewLinks();
+    ML.initEventListeners();
+    ML.initFileWatch();
+    ML.initUnsavedWarning();
+    ML.initSidebar();
+    ML.initSearchBar();
+    var settings = ML.loadSettings();
+    ML.setViewMode(settings.viewMode || 'split');
+  };
+
+  if (document.readyState === 'loading') {
+    document.addEventListener('DOMContentLoaded', ML.init);
+  } else {
+    ML.init();
+  }
+})();
diff --git a/renderer/editor.js b/renderer/editor.js
new file mode 100644
index 0000000..fd3fa37
--- /dev/null
+++ b/renderer/editor.js
@@ -0,0 +1,147 @@
+// MarkLite — Editor Module: line numbers, cursor, file size, scroll sync
+(function () {
+  'use strict';
+  var ML = window.MarkLite;
+
+  // ===== Line Numbers =====
+  function countNewlines(text) {
+    var count = 1;
+    for (var i = 0, len = text.length; i < len; i++) {
+      if (text.charCodeAt(i) === 10) count++;
+    }
+    return count;
+  }
+
+  ML.updateLineNumbers = function () {
+    var count = countNewlines(ML.editor.value);
+    if (count === ML.lineCountCache) return;
+    ML.lineCountCache = count;
+    if (count > 2000) {
+      ML.renderVirtualLineNumbers(count);
+    } else {
+      var arr = new Array(count);
+      for (var i = 0; i < count; i++) arr[i] = '<div class="line-num">' + (i + 1) + '</div>';
+      ML.lineNumbers.innerHTML = arr.join('');
+    }
+  };
+
+  ML.renderVirtualLineNumbers = function (totalLines) {
+    var lineHeight = 20.8;
+    var scrollTop = ML.editor.scrollTop;
+    var viewportHeight = ML.editor.clientHeight;
+    var buffer = 20;
+    var startLine = Math.max(0, Math.floor(scrollTop / lineHeight) - buffer);
+    var endLine = Math.min(totalLines, Math.ceil((scrollTop + viewportHeight) / lineHeight) + buffer);
+    var visibleCount = endLine - startLine;
+    var topPadding = startLine * lineHeight;
+    var bottomPadding = (totalLines - endLine) * lineHeight;
+    var arr = new Array(visibleCount + 2);
+    arr[0] = '<div style="height:' + topPadding + 'px"></div>';
+    for (var i = 0; i < visibleCount; i++) arr[i + 1] = '<div class="line-num">' + (startLine + i + 1) + '</div>';
+    arr[visibleCount + 1] = '<div style="height:' + bottomPadding + 'px"></div>';
+    ML.lineNumbers.innerHTML = arr.join('');
+  };
+
+  // ===== Cursor Position =====
+  ML.updateCursorPosition = function () {
+    var text = ML.editor.value;
+    var pos = ML.editor.selectionStart;
+    var textBefore = text.substring(0, pos);
+    var lines = textBefore.split('\n');
+    ML.statusCursor.textContent = '行 ' + lines.length + ', 列 ' + (lines[lines.length - 1].length + 1);
+  };
+
+  // ===== File Size =====
+  ML.updateFileSize = function () {
+    var bytes = new Blob([ML.editor.value]).size;
+    ML.statusSize.textContent = ML.formatBytes(bytes);
+    ML.statusSizeDivider.classList.add('visible');
+  };
+
+  // ===== Scroll Sync =====
+  var previewPositions = null;
+  var lineToPreviewMap = null;
+
+  ML.cachePreviewPositions = function () {
+    previewPositions = [];
+    for (var i = 0; i < ML.preview.children.length; i++) previewPositions.push(ML.preview.children[i].offsetTop);
+    buildLineToPreviewMap();
+  };
+
+  function buildLineToPreviewMap() {
+    if (!previewPositions || previewPositions.length === 0) { lineToPreviewMap = null; return; }
+    var text = ML.editor.value;
+    var lines = text.split('\n');
+    var totalLines = lines.length;
+    var blockStartLines = [];
+    var inCodeBlock = false;
+    for (var i = 0; i < totalLines; i++) {
+      var trimmed = lines[i].trimStart();
+      if (trimmed.startsWith('```')) {
+        if (!inCodeBlock) { blockStartLines.push(i); inCodeBlock = true; }
+        else inCodeBlock = false;
+        continue;
+      }
+      if (inCodeBlock) continue;
+      if (trimmed.startsWith('#') || trimmed.startsWith('- ') || trimmed.startsWith('* ') || trimmed.startsWith('+ ') ||
+          /^\d+\.\s/.test(trimmed) || trimmed.startsWith('> ') || trimmed.startsWith('|') ||
+          trimmed.startsWith('---') || trimmed.startsWith('***') || trimmed.startsWith('___') ||
+          (trimmed === '' && i > 0 && lines[i - 1].trim() === '')) {
+        blockStartLines.push(i);
+      }
+    }
+    var uniqueStartsArr = [].concat(_toConsumableArray(new Set(blockStartLines))).sort(function (a, b) { return a - b; });
+    var uniqueStartsSet = new Set(uniqueStartsArr);
+    lineToPreviewMap = new Float32Array(totalLines);
+    if (uniqueStartsArr.length === 0) {
+      for (var _i = 0; _i < totalLines; _i++) lineToPreviewMap[_i] = (_i / Math.max(1, totalLines - 1)) * previewPositions[previewPositions.length - 1];
+      return;
+    }
+    var domCount = previewPositions.length;
+    for (var _i2 = 0; _i2 < uniqueStartsArr.length; _i2++) {
+      var lineIdx = uniqueStartsArr[_i2];
+      var domIdx = Math.min(Math.floor((_i2 / uniqueStartsArr.length) * domCount), domCount - 1);
+      lineToPreviewMap[lineIdx] = previewPositions[domIdx];
+    }
+    for (var _i3 = 0; _i3 < totalLines; _i3++) {
+      if (lineToPreviewMap[_i3] !== 0 && uniqueStartsSet.has(_i3)) continue;
+      var prevLine = -1, nextLine = -1;
+      for (var j = _i3 - 1; j >= 0; j--) { if (lineToPreviewMap[j] !== 0 || uniqueStartsSet.has(j)) { prevLine = j; break; } }
+      for (var _j = _i3 + 1; _j < totalLines; _j++) { if (lineToPreviewMap[_j] !== 0 || uniqueStartsSet.has(_j)) { nextLine = _j; break; } }
+      if (prevLine === -1 && nextLine === -1) lineToPreviewMap[_i3] = 0;
+      else if (prevLine === -1) lineToPreviewMap[_i3] = lineToPreviewMap[nextLine];
+      else if (nextLine === -1) lineToPreviewMap[_i3] = lineToPreviewMap[prevLine];
+      else { var ratio = (_i3 - prevLine) / (nextLine - prevLine); lineToPreviewMap[_i3] = lineToPreviewMap[prevLine] + ratio * (lineToPreviewMap[nextLine] - lineToPreviewMap[prevLine]); }
+    }
+  }
+
+  function _toConsumableArray(arr) { if (Array.isArray(arr)) { for (var i = 0, arr2 = new Array(arr.length); i < arr.length; i++) arr2[i] = arr[i]; return arr2; } return Array.from(arr); }
+
+  ML.syncScroll = function () {
+    if (ML.viewMode !== 'split') return;
+    var lineHeight = parseFloat(getComputedStyle(ML.editor).lineHeight) || 20.8;
+    var scrollTop = ML.editor.scrollTop;
+    var topLine = Math.floor(scrollTop / lineHeight);
+    if (!previewPositions || previewPositions.length === 0) ML.cachePreviewPositions();
+    if (!previewPositions || previewPositions.length === 0) return;
+    if (lineToPreviewMap && topLine >= 0 && topLine < lineToPreviewMap.length) {
+      ML.previewPanel.scrollTop = lineToPreviewMap[topLine];
+    } else {
+      var totalLines = ML.editor.value.split('\n').length;
+      var ratio = totalLines > 1 ? topLine / (totalLines - 1) : 0;
+      var targetIndex = Math.min(Math.floor(ratio * previewPositions.length), previewPositions.length - 1);
+      if (targetIndex >= 0 && previewPositions[targetIndex] !== undefined) ML.previewPanel.scrollTop = previewPositions[targetIndex];
+    }
+  };
+
+  // ===== Schedule Update =====
+  ML.scheduleUpdate = function () {
+    if (ML.updateTimer) clearTimeout(ML.updateTimer);
+    ML.updateTimer = setTimeout(function () {
+      ML.renderMarkdown(ML.editor.value);
+      ML.updateLineNumbers();
+      ML.updateFileSize();
+      ML.cachePreviewPositions();
+    }, 150);
+  };
+})();
diff --git a/renderer/index.html b/renderer/index.html
index 9913871..fc63807 100644
--- a/renderer/index.html
+++ b/renderer/index.html
@@ -210,6 +210,11 @@
 
   <script src="../lib/marked.min.js"></script>
   <script src="../lib/highlight.min.js"></script>
-  <script src="renderer.js"></script>
+  <script src="markdown.js"></script>
+  <script src="editor.js"></script>
+  <script src="tabs.js"></script>
+  <script src="search.js"></script>
+  <script src="sidebar.js"></script>
+  <script src="core.js"></script>
 </body>
 </html>
diff --git a/renderer/markdown.js b/renderer/markdown.js
new file mode 100644
index 0000000..7fd95e6
--- /dev/null
+++ b/renderer/markdown.js
@@ -0,0 +1,103 @@
+// MarkLite — Markdown Module: marked.js init, sanitizer, rendering, preview links
+(function () {
+  'use strict';
+  var ML = window.MarkLite;
+
+  // ===== HTML Sanitizer =====
+  var DANGEROUS_TAGS = new Set(['script', 'iframe', 'object', 'embed', 'applet', 'form', 'base', 'meta', 'link', 'style']);
+  var DANGEROUS_ATTRS = new Set([
+    'onabort', 'onanimationend', 'onanimationiteration', 'onanimationstart', 'onauxclick', 'onbeforecopy', 'onbeforecut',
+    'onbeforepaste', 'onblur', 'oncancel', 'oncanplay', 'oncanplaythrough', 'onchange', 'onclick', 'onclose', 'oncontextmenu',
+    'oncopy', 'oncuechange', 'oncut', 'ondblclick', 'ondrag', 'ondragend', 'ondragenter', 'ondragleave', 'ondragover',
+    'ondragstart', 'ondrop', 'ondurationchange', 'onemptied', 'onended', 'onerror', 'onfocus', 'onfocusin', 'onfocusout',
+    'onfullscreenchange', 'onfullscreenerror', 'ongotpointercapture', 'oninput', 'oninvalid', 'onkeydown', 'onkeypress',
+    'onkeyup', 'onload', 'onloadeddata', 'onloadedmetadata', 'onloadstart', 'onlostpointercapture', 'onmousedown',
+    'onmouseenter', 'onmouseleave', 'onmousemove', 'onmouseout', 'onmouseover', 'onmouseup', 'onmousewheel', 'onpaste',
+    'onpause', 'onplay', 'onplaying', 'onpointercancel', 'onpointerdown', 'onpointerenter', 'onpointerleave', 'onpointermove',
+    'onpointerout', 'onpointerover', 'onpointerup', 'onprogress', 'onratechange', 'onreset', 'onresize', 'onscroll',
+    'onsearch', 'onseeked', 'onseeking', 'onselect', 'onselectionchange', 'onselectstart', 'onshow', 'onstalled', 'onsubmit',
+    'onsuspend', 'ontimeupdate', 'ontoggle', 'ontouchcancel', 'ontouchend', 'ontouchmove', 'ontouchstart', 'ontransitionend',
+    'onvolumechange', 'onwaiting', 'onwheel', 'onanimationend', 'oncontentvisibilityautostatechange', 'onscrollend',
+    'onscrollsnapchange', 'onscrollsnapchanging'
+  ]);
+
+  function sanitizeHTML(html) {
+    var doc = new DOMParser().parseFromString(html, 'text/html');
+    var walker = document.createTreeWalker(doc.body, NodeFilter.SHOW_ELEMENT);
+    var toRemove = [];
+    while (walker.nextNode()) {
+      var el = walker.currentNode;
+      var tag = el.tagName.toLowerCase();
+      if (DANGEROUS_TAGS.has(tag)) { toRemove.push(el); continue; }
+      var attrs = Array.from(el.attributes);
+      for (var i = 0; i < attrs.length; i++) {
+        var name = attrs[i].name.toLowerCase();
+        if (DANGEROUS_ATTRS.has(name) || name.startsWith('on')) el.removeAttribute(attrs[i].name);
+        else if ((name === 'href' || name === 'action' || name === 'formaction' || name === 'xlink:href') && /^\s*javascript:/i.test(attrs[i].value)) el.removeAttribute(attrs[i].name);
+        else if (name === 'style' && /expression\s*\(|url\s*\(\s*['"]?\s*javascript:/i.test(attrs[i].value)) el.removeAttribute(attrs[i].name);
+      }
+    }
+    for (var _i = 0; _i < toRemove.length; _i++) toRemove[_i].parentNode.removeChild(toRemove[_i]);
+    return doc.body.innerHTML;
+  }
+
+  // ===== Rendering =====
+  ML.renderMarkdown = function (text) {
+    if (typeof marked === 'undefined') { ML.preview.textContent = '错误: Markdown 解析库未加载'; ML.preview.style.color = 'red'; return; }
+    try {
+      var raw = marked.parse(text);
+      ML.preview.innerHTML = sanitizeHTML(raw);
+      ML.preview.style.color = '';
+    } catch (e) { ML.preview.textContent = '渲染错误: ' + e.message; ML.preview.style.color = 'red'; }
+  };
+
+  // ===== Init marked.js =====
+  ML.initMarked = function () {
+    if (typeof marked === 'undefined') return;
+    var renderer = new marked.Renderer();
+    renderer.code = function (codeOrToken, legacyLang) {
+      var text = (typeof codeOrToken === 'object' && codeOrToken !== null) ? codeOrToken.text : codeOrToken;
+      var lang = (typeof codeOrToken === 'object' && codeOrToken !== null) ? codeOrToken.lang : legacyLang;
+      var highlighted = text;
+      if (typeof hljs !== 'undefined') {
+        if (lang && hljs.getLanguage(lang)) { try { highlighted = hljs.highlight(text, { language: lang }).value; } catch (e) { /* */ } }
+        else { try { highlighted = hljs.highlightAuto(text).value; } catch (e) { /* */ } }
+      }
+      var langClass = lang ? ' language-' + lang : '';
+      return '<pre><code class="hljs' + langClass + '">' + highlighted + '</code></pre>';
+    };
+    renderer.image = function (hrefOrToken, title, text) {
+      var href = (typeof hrefOrToken === 'object' && hrefOrToken !== null) ? hrefOrToken.href : hrefOrToken;
+      var alt = (typeof hrefOrToken === 'object' && hrefOrToken !== null) ? hrefOrToken.text : text;
+      var titleAttr = (typeof hrefOrToken === 'object' && hrefOrToken !== null) ? hrefOrToken.title : title;
+      var src = href;
+      if (src && !src.startsWith('http://') && !src.startsWith('https://') && !src.startsWith('data:') && !src.startsWith('file://')) {
+        var tab = ML.getActiveTab();
+        if (tab && tab.filePath) {
+          var dir = tab.filePath.replace(/[/\\][^/\\]+$/, '');
+          var sep = dir.includes('\\') ? '\\' : '/';
+          src = 'file://' + (dir + sep + src).replace(/\\/g, '/');
+        }
+      }
+      var titleStr = titleAttr ? ' title="' + titleAttr + '"' : '';
+      return '<img src="' + src + '" alt="' + alt + '"' + titleStr + '>';
+    };
+    marked.setOptions({ gfm: true, breaks: true, pedantic: false });
+    marked.use({ renderer: renderer });
+  };
+
+  // ===== Preview Links =====
+  ML.initPreviewLinks = function () {
+    ML.preview.addEventListener('click', function (e) {
+      var link = e.target.closest('a');
+      if (!link) return;
+      e.preventDefault();
+      var href = link.getAttribute('href');
+      if (!href) return;
+      if (href.startsWith('#')) { var target = ML.preview.querySelector(href); if (target) target.scrollIntoView({ behavior: 'smooth' }); return; }
+      try { var url = new URL(href); if (url.protocol !== 'http:' && url.protocol !== 'https:') return; } catch (err) { return; }
+      if (typeof window.electronAPI !== 'undefined' && window.electronAPI.openExternal) window.electronAPI.openExternal(href);
+      else window.open(href, '_blank', 'noopener');
+    });
+  };
+})();
diff --git a/renderer/renderer.js b/renderer/renderer.js
deleted file mode 100644
index b5e0590..0000000
--- a/renderer/renderer.js
+++ /dev/null
@@ -1,1663 +0,0 @@
-// MarkLite Renderer Process
-(function () {
-  'use strict';
-
-  // ===== DOM Elements =====
-  const editor = document.getElementById('editor');
-  const preview = document.getElementById('preview');
-  const lineNumbers = document.getElementById('line-numbers');
-  const welcomeScreen = document.getElementById('welcome-screen');
-  const dropOverlay = document.getElementById('drop-overlay');
-  const modifiedBanner = document.getElementById('modified-banner');
-  const statusText = document.getElementById('status-text');
-  const statusCursor = document.getElementById('status-cursor');
-  const statusSize = document.getElementById('status-size');
-  const statusSizeDivider = document.querySelector('.status-size-divider');
-  const resizer = document.getElementById('resizer');
-  const editorPanel = document.getElementById('editor-panel');
-  const previewPanel = document.getElementById('preview-panel');
-  const mainContent = document.getElementById('main-content');
-  const contentWrapper = document.getElementById('content-wrapper');
-  const tabList = document.getElementById('tab-list');
-
-  // Sidebar
-  const sidebar = document.getElementById('sidebar');
-  const sidebarTree = document.getElementById('sidebar-tree');
-  const btnOpenFolder = document.getElementById('btn-open-folder');
-
-  // Search
-  const searchBar = document.getElementById('search-bar');
-  const searchInput = document.getElementById('search-input');
-  const replaceInput = document.getElementById('replace-input');
-  const searchCount = document.getElementById('search-count');
-  const replaceRow = document.getElementById('replace-row');
-  const btnCase = document.getElementById('btn-case');
-  const btnRegex = document.getElementById('btn-regex');
-  const btnNext = document.getElementById('btn-next');
-  const btnPrev = document.getElementById('btn-prev');
-  const btnSearchClose = document.getElementById('btn-search-close');
-  const btnReplace = document.getElementById('btn-replace');
-  const btnReplaceAll = document.getElementById('btn-replace-all');
-
-  // Buttons
-  const btnOpen = document.getElementById('btn-open');
-  const btnSave = document.getElementById('btn-save');
-  const btnSplit = document.getElementById('btn-split');
-  const btnEditor = document.getElementById('btn-editor');
-  const btnPreview = document.getElementById('btn-preview');
-  const btnWelcomeOpen = document.getElementById('btn-welcome-open');
-  const btnWelcomeNew = document.getElementById('btn-welcome-new');
-  const btnDark = document.getElementById('btn-dark');
-  const btnReload = document.getElementById('btn-reload');
-  const btnDismiss = document.getElementById('btn-dismiss');
-  const btnNewTab = document.getElementById('btn-new-tab');
-
-  // ===== Tab State =====
-  let tabs = [];       // Array of tab objects
-  let activeTabId = null;
-  let tabIdCounter = 0;
-  let mruTabStack = []; // Most-recently-used tab IDs for Ctrl+Tab
-
-  // ===== Other State =====
-  let viewMode = 'split';
-  let updateTimer = null;
-  let lineCountCache = 0;
-  let currentRootPath = null;
-
-  // Search state
-  let searchMatches = [];
-  let searchIndex = -1;
-  let searchCaseSensitive = false;
-  let searchUseRegex = false;
-
-  // ===== Character Width Measurement (#1) =====
-  const _charWidthCanvas = document.createElement('canvas');
-  const _charWidthCtx = _charWidthCanvas.getContext('2d');
-  let _cachedCharWidth = null;
-  function getCharWidth() {
-    if (_cachedCharWidth !== null) return _cachedCharWidth;
-    const style = getComputedStyle(editor);
-    _charWidthCtx.font = `${style.fontSize} ${style.fontFamily}`;
-    _cachedCharWidth = _charWidthCtx.measureText('M').width;
-    return _cachedCharWidth;
-  }
-  // Recalculate on font/theme change
-  new MutationObserver(() => { _cachedCharWidth = null; }).observe(document.documentElement, { attributes: true, attributeFilter: ['class'] });
-
-  // ===== Toast Notification (#5) =====
-  function showToast(message, duration) {
-    duration = duration || 3000;
-    let toast = document.getElementById('toast-notification');
-    if (!toast) {
-      toast = document.createElement('div');
-      toast.id = 'toast-notification';
-      document.getElementById('app').appendChild(toast);
-    }
-    toast.textContent = message;
-    toast.classList.add('show');
-    clearTimeout(toast._timer);
-    toast._timer = setTimeout(() => toast.classList.remove('show'), duration);
-  }
-
-  // ===== Tab Object =====
-  function createTab(filePath, content) {
-    const id = ++tabIdCounter;
-    return {
-      id,
-      filePath: filePath || null,
-      content: content || '',
-      isModified: false,
-      scrollTop: 0,
-      scrollLeft: 0,
-      selectionStart: 0,
-      selectionEnd: 0,
-      previewScrollTop: 0
-    };
-  }
-
-  // ===== localStorage Helpers =====
-  function loadSettings() {
-    try {
-      return JSON.parse(localStorage.getItem('marklite-settings') || '{}');
-    } catch { return {}; }
-  }
-
-  function saveSetting(key, value) {
-    try {
-      const s = loadSettings();
-      s[key] = value;
-      localStorage.setItem('marklite-settings', JSON.stringify(s));
-    } catch { /* ignore */ }
-  }
-
-  // ===== Dark Mode =====
-  function initDarkMode() {
-    const settings = loadSettings();
-    const iconDark = document.getElementById('icon-dark');
-    const iconLight = document.getElementById('icon-light');
-
-    function apply(isDark) {
-      document.documentElement.classList.toggle('dark', isDark);
-      iconDark.style.display = isDark ? 'none' : '';
-      iconLight.style.display = isDark ? '' : 'none';
-    }
-
-    // Respect system preference if no saved setting
-    const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
-    apply(settings.darkMode !== undefined ? !!settings.darkMode : prefersDark);
-
-    btnDark.addEventListener('click', () => {
-      const isDark = !document.documentElement.classList.contains('dark');
-      apply(isDark);
-      saveSetting('darkMode', isDark);
-    });
-  }
-
-  // ===== Initialize marked.js =====
-  function initMarked() {
-    if (typeof marked !== 'undefined') {
-      const renderer = new marked.Renderer();
-      // 兼容 marked v4（positional args）和 v9+（token object）
-      renderer.code = function (codeOrToken, legacyLang) {
-        const text = (typeof codeOrToken === 'object' && codeOrToken !== null)
-          ? codeOrToken.text
-          : codeOrToken;
-        const lang = (typeof codeOrToken === 'object' && codeOrToken !== null)
-          ? codeOrToken.lang
-          : legacyLang;
-        let highlighted = text;
-        if (typeof hljs !== 'undefined') {
-          if (lang && hljs.getLanguage(lang)) {
-            try { highlighted = hljs.highlight(text, { language: lang }).value; } catch (e) { /* fallback */ }
-          } else {
-            try { highlighted = hljs.highlightAuto(text).value; } catch (e) { /* fallback */ }
-          }
-        }
-        const langClass = lang ? ` language-${lang}` : '';
-        return `<pre><code class="hljs${langClass}">${highlighted}</code></pre>`;
-      };
-      // 处理相对路径图片 → file:// URL
-      renderer.image = function (hrefOrToken, title, text) {
-        const href = (typeof hrefOrToken === 'object' && hrefOrToken !== null)
-          ? hrefOrToken.href
-          : hrefOrToken;
-        const alt = (typeof hrefOrToken === 'object' && hrefOrToken !== null)
-          ? hrefOrToken.text
-          : text;
-        const titleAttr = (typeof hrefOrToken === 'object' && hrefOrToken !== null)
-          ? hrefOrToken.title
-          : title;
-        let src = href;
-        // 相对路径转绝对路径
-        if (src && !src.startsWith('http://') && !src.startsWith('https://') && !src.startsWith('data:') && !src.startsWith('file://')) {
-          const tab = getActiveTab();
-          if (tab && tab.filePath) {
-            const dir = tab.filePath.replace(/[/\\][^/\\]+$/, '');
-            // 简单路径拼接（不依赖 require('path')）
-            const sep = dir.includes('\\') ? '\\' : '/';
-            src = 'file://' + (dir + sep + src).replace(/\\/g, '/');
-          }
-        }
-        const titleStr = titleAttr ? ` title="${titleAttr}"` : '';
-        return `<img src="${src}" alt="${alt}"${titleStr}>`;
-      };
-      marked.setOptions({ gfm: true, breaks: true, pedantic: false });
-      marked.use({ renderer });
-    }
-  }
-
-  // ===== HTML Sanitizer =====
-  // 移除事件处理器、危险元素和 javascript: 协议，防止 XSS
-  const DANGEROUS_TAGS = new Set([
-    'script', 'iframe', 'object', 'embed', 'applet', 'form',
-    'base', 'meta', 'link', 'style'
-  ]);
-  const DANGEROUS_ATTRS = new Set([
-    'onabort', 'onanimationend', 'onanimationiteration', 'onanimationstart',
-    'onauxclick', 'onbeforecopy', 'onbeforecut', 'onbeforepaste', 'onblur',
-    'oncancel', 'oncanplay', 'oncanplaythrough', 'onchange', 'onclick',
-    'onclose', 'oncontextmenu', 'oncopy', 'oncuechange', 'oncut',
-    'ondblclick', 'ondrag', 'ondragend', 'ondragenter', 'ondragleave',
-    'ondragover', 'ondragstart', 'ondrop', 'ondurationchange', 'onemptied',
-    'onended', 'onerror', 'onfocus', 'onfocusin', 'onfocusout',
-    'onfullscreenchange', 'onfullscreenerror', 'ongotpointercapture',
-    'oninput', 'oninvalid', 'onkeydown', 'onkeypress', 'onkeyup',
-    'onload', 'onloadeddata', 'onloadedmetadata', 'onloadstart',
-    'onlostpointercapture', 'onmousedown', 'onmouseenter', 'onmouseleave',
-    'onmousemove', 'onmouseout', 'onmouseover', 'onmouseup', 'onmousewheel',
-    'onpaste', 'onpause', 'onplay', 'onplaying', 'onpointercancel',
-    'onpointerdown', 'onpointerenter', 'onpointerleave', 'onpointermove',
-    'onpointerout', 'onpointerover', 'onpointerup', 'onprogress',
-    'onratechange', 'onreset', 'onresize', 'onscroll', 'onsearch',
-    'onseeked', 'onseeking', 'onselect', 'onselectionchange',
-    'onselectstart', 'onshow', 'onstalled', 'onsubmit', 'onsuspend',
-    'ontimeupdate', 'ontoggle', 'ontouchcancel', 'ontouchend',
-    'ontouchmove', 'ontouchstart', 'ontransitionend', 'onvolumechange',
-    'onwaiting', 'onwheel', 'onanimationend', 'oncontentvisibilityautostatechange',
-    'onscrollend', 'onscrollsnapchange', 'onscrollsnapchanging'
-  ]);
-
-  function sanitizeHTML(html) {
-    // 用 DOMParser 解析（不会执行脚本）
-    const doc = new DOMParser().parseFromString(html, 'text/html');
-    const walker = document.createTreeWalker(doc.body, NodeFilter.SHOW_ELEMENT);
-    const toRemove = [];
-
-    while (walker.nextNode()) {
-      const el = walker.currentNode;
-      const tag = el.tagName.toLowerCase();
-
-      // 移除危险元素
-      if (DANGEROUS_TAGS.has(tag)) {
-        toRemove.push(el);
-        continue;
-      }
-
-      // 移除危险属性（on* 事件处理器 + javascript: 协议）
-      for (const attr of Array.from(el.attributes)) {
-        const name = attr.name.toLowerCase();
-        if (DANGEROUS_ATTRS.has(name) || name.startsWith('on')) {
-          el.removeAttribute(attr.name);
-        } else if (
-          (name === 'href' || name === 'action' || name === 'formaction' || name === 'xlink:href') &&
-          /^\s*javascript:/i.test(attr.value)
-        ) {
-          el.removeAttribute(attr.name);
-        } else if (name === 'style' && /expression\s*\(|url\s*\(\s*['"]?\s*javascript:/i.test(attr.value)) {
-          el.removeAttribute(attr.name);
-        }
-      }
-    }
-
-    // 批量移除危险元素
-    for (const el of toRemove) {
-      el.parentNode.removeChild(el);
-    }
-
-    return doc.body.innerHTML;
-  }
-
-  // ===== Markdown Rendering =====
-  function renderMarkdown(text) {
-    if (typeof marked === 'undefined') {
-      preview.textContent = '错误: Markdown 解析库未加载';
-      preview.style.color = 'red';
-      return;
-    }
-    try {
-      const raw = marked.parse(text);
-      preview.innerHTML = sanitizeHTML(raw);
-      preview.style.color = '';
-    } catch (e) {
-      preview.textContent = '渲染错误: ' + e.message;
-      preview.style.color = 'red';
-    }
-  }
-
-  // Intercept link clicks in preview — open in system browser
-  function initPreviewLinks() {
-    preview.addEventListener('click', (e) => {
-      const link = e.target.closest('a');
-      if (!link) return;
-      e.preventDefault();
-      const href = link.getAttribute('href');
-      if (!href) return;
-      // Anchor links: scroll within preview
-      if (href.startsWith('#')) {
-        const target = preview.querySelector(href);
-        if (target) target.scrollIntoView({ behavior: 'smooth' });
-        return;
-      }
-      // Only allow http/https protocols
-      try {
-        const url = new URL(href);
-        if (url.protocol !== 'http:' && url.protocol !== 'https:') return;
-      } catch {
-        // Relative URLs fail new URL(), but we already handled anchors above
-        return;
-      }
-      // External links: open in system browser
-      if (typeof window.electronAPI !== 'undefined' && window.electronAPI.openExternal) {
-        window.electronAPI.openExternal(href);
-      } else {
-        window.open(href, '_blank', 'noopener');
-      }
-    });
-  }
-
-  // ===== Line Numbers =====
-  // 快速计算换行符数量，避免 split 产生大数组
-  function countNewlines(text) {
-    let count = 1;
-    for (let i = 0, len = text.length; i < len; i++) {
-      if (text.charCodeAt(i) === 10) count++; // '\n' = 0x0A
-    }
-    return count;
-  }
-
-  function updateLineNumbers() {
-    const count = countNewlines(editor.value);
-    if (count === lineCountCache) return;
-    lineCountCache = count;
-
-    // 大文件（>2000 行）时用虚拟化：只渲染可视区域的行号
-    const LARGE_FILE_THRESHOLD = 2000;
-    if (count > LARGE_FILE_THRESHOLD) {
-      renderVirtualLineNumbers(count);
-    } else {
-      // 小文件：一次性生成全部行号（使用数组 join 比字符串拼接快）
-      const arr = new Array(count);
-      for (let i = 0; i < count; i++) {
-        arr[i] = '<div class="line-num">' + (i + 1) + '</div>';
-      }
-      lineNumbers.innerHTML = arr.join('');
-    }
-  }
-
-  // 虚拟化行号：只渲染当前可视区域附近的行号
-  function renderVirtualLineNumbers(totalLines) {
-    const lineHeight = 20.8; // 与 CSS line-height 一致
-    const scrollTop = editor.scrollTop;
-    const viewportHeight = editor.clientHeight;
-    const buffer = 20; // 上下缓冲行数
-
-    const startLine = Math.max(0, Math.floor(scrollTop / lineHeight) - buffer);
-    const endLine = Math.min(totalLines, Math.ceil((scrollTop + viewportHeight) / lineHeight) + buffer);
-    const visibleCount = endLine - startLine;
-
-    // 顶部占位
-    const topPadding = startLine * lineHeight;
-    // 底部占位
-    const bottomPadding = (totalLines - endLine) * lineHeight;
-
-    const arr = new Array(visibleCount + 2);
-    arr[0] = '<div style="height:' + topPadding + 'px"></div>';
-    for (let i = 0; i < visibleCount; i++) {
-      arr[i + 1] = '<div class="line-num">' + (startLine + i + 1) + '</div>';
-    }
-    arr[visibleCount + 1] = '<div style="height:' + bottomPadding + 'px"></div>';
-    lineNumbers.innerHTML = arr.join('');
-  }
-
-  // ===== Cursor Position =====
-  function updateCursorPosition() {
-    const text = editor.value;
-    const pos = editor.selectionStart;
-    const textBefore = text.substring(0, pos);
-    const lines = textBefore.split('\n');
-    statusCursor.textContent = `行 ${lines.length}, 列 ${lines[lines.length - 1].length + 1}`;
-  }
-
-  // ===== File Size =====
-  function formatBytes(bytes) {
-    if (bytes < 1024) return bytes + ' B';
-    if (bytes < 1024 * 1024) return (bytes / 1024).toFixed(1) + ' KB';
-    return (bytes / (1024 * 1024)).toFixed(1) + ' MB';
-  }
-
-  function updateFileSize() {
-    const bytes = new Blob([editor.value]).size;
-    statusSize.textContent = formatBytes(bytes);
-    statusSizeDivider.classList.add('visible');
-  }
-
-  // ===== Scroll Sync =====
-  let previewPositions = null;
-  let lineToPreviewMap = null; // 行号 → 预览像素位置的映射
-
-  function cachePreviewPositions() {
-    previewPositions = [];
-    for (let i = 0; i < preview.children.length; i++) {
-      previewPositions.push(preview.children[i].offsetTop);
-    }
-    // 构建行号→预览位置的映射表
-    buildLineToPreviewMap();
-  }
-
-  // 通过分析原始 Markdown 文本，建立编辑器行号到预览 DOM 位置的映射
-  function buildLineToPreviewMap() {
-    if (!previewPositions || previewPositions.length === 0) {
-      lineToPreviewMap = null;
-      return;
-    }
-
-    const text = editor.value;
-    const lines = text.split('\n');
-    const totalLines = lines.length;
-
-    // 找出每个"块级元素"在编辑器中的起始行
-    // 块级元素：标题、段落、代码块、列表、引用、表格、水平线
-    const blockStartLines = [];
-    let inCodeBlock = false;
-
-    for (let i = 0; i < totalLines; i++) {
-      const line = lines[i];
-      const trimmed = line.trimStart();
-
-      // 围栏代码块边界
-      if (trimmed.startsWith('```')) {
-        if (!inCodeBlock) {
-          blockStartLines.push(i);
-          inCodeBlock = true;
-        } else {
-          inCodeBlock = false;
-        }
-        continue;
-      }
-
-      if (inCodeBlock) continue;
-
-      // 块级元素起始行
-      if (
-        trimmed.startsWith('#') ||           // 标题
-        trimmed.startsWith('- ') ||           // 无序列表
-        trimmed.startsWith('* ') ||           // 无序列表
-        trimmed.startsWith('+ ') ||           // 无序列表
-        /^\d+\.\s/.test(trimmed) ||           // 有序列表
-        trimmed.startsWith('> ') ||           // 引用
-        trimmed.startsWith('|') ||            // 表格
-        trimmed.startsWith('---') ||          // 水平线
-        trimmed.startsWith('***') ||          // 水平线
-        trimmed.startsWith('___') ||          // 水平线
-        (trimmed === '' && i > 0 && lines[i - 1].trim() === '') // 连续空行=段落分隔
-      ) {
-        blockStartLines.push(i);
-      }
-    }
-
-    // 去重并排序
-    const uniqueStartsArr = [...new Set(blockStartLines)].sort((a, b) => a - b);
-    const uniqueStartsSet = new Set(uniqueStartsArr);
-
-    // 将编辑器行号映射到预览 DOM 位置
-    // 每个块的起始行对应一个预览元素，用线性插值填充中间行
-    lineToPreviewMap = new Float32Array(totalLines);
-
-    if (uniqueStartsArr.length === 0) {
-      // 没有找到块边界，回退到线性映射
-      for (let i = 0; i < totalLines; i++) {
-        lineToPreviewMap[i] = (i / Math.max(1, totalLines - 1)) * previewPositions[previewPositions.length - 1];
-      }
-      return;
-    }
-
-    // 将块起始行映射到预览 DOM 索引
-    const domCount = previewPositions.length;
-    for (let i = 0; i < uniqueStartsArr.length; i++) {
-      const lineIdx = uniqueStartsArr[i];
-      const domIdx = Math.min(Math.floor((i / uniqueStartsArr.length) * domCount), domCount - 1);
-      lineToPreviewMap[lineIdx] = previewPositions[domIdx];
-    }
-
-    // 线性插值填充所有行
-    for (let i = 0; i < totalLines; i++) {
-      if (lineToPreviewMap[i] !== 0 && uniqueStartsSet.has(i)) continue;
-
-      // 找到前后最近的已映射行
-      let prevLine = -1, nextLine = -1;
-      for (let j = i - 1; j >= 0; j--) {
-        if (lineToPreviewMap[j] !== 0 || uniqueStartsSet.has(j)) { prevLine = j; break; }
-      }
-      for (let j = i + 1; j < totalLines; j++) {
-        if (lineToPreviewMap[j] !== 0 || uniqueStartsSet.has(j)) { nextLine = j; break; }
-      }
-
-      if (prevLine === -1 && nextLine === -1) {
-        lineToPreviewMap[i] = 0;
-      } else if (prevLine === -1) {
-        lineToPreviewMap[i] = lineToPreviewMap[nextLine];
-      } else if (nextLine === -1) {
-        lineToPreviewMap[i] = lineToPreviewMap[prevLine];
-      } else {
-        // 线性插值
-        const ratio = (i - prevLine) / (nextLine - prevLine);
-        lineToPreviewMap[i] = lineToPreviewMap[prevLine] + ratio * (lineToPreviewMap[nextLine] - lineToPreviewMap[prevLine]);
-      }
-    }
-  }
-
-  function syncScroll() {
-    if (viewMode !== 'split') return;
-    const lineHeight = parseFloat(getComputedStyle(editor).lineHeight) || 20.8;
-    const scrollTop = editor.scrollTop;
-    const topLine = Math.floor(scrollTop / lineHeight);
-
-    if (!previewPositions || previewPositions.length === 0) cachePreviewPositions();
-    if (!previewPositions || previewPositions.length === 0) return;
-
-    // 使用行号→预览位置映射表
-    if (lineToPreviewMap && topLine >= 0 && topLine < lineToPreviewMap.length) {
-      previewPanel.scrollTop = lineToPreviewMap[topLine];
-    } else {
-      // fallback: 线性比例映射
-      const totalLines = editor.value.split('\n').length;
-      const ratio = totalLines > 1 ? topLine / (totalLines - 1) : 0;
-      const targetIndex = Math.min(Math.floor(ratio * previewPositions.length), previewPositions.length - 1);
-      if (targetIndex >= 0 && previewPositions[targetIndex] !== undefined) {
-        previewPanel.scrollTop = previewPositions[targetIndex];
-      }
-    }
-  }
-
-  // ===== Schedule Update =====
-  function scheduleUpdate() {
-    if (updateTimer) clearTimeout(updateTimer);
-    updateTimer = setTimeout(() => {
-      renderMarkdown(editor.value);
-      updateLineNumbers();
-      updateFileSize();
-      cachePreviewPositions();
-    }, 150);
-  }
-
-  // ===== Helper =====
-  function getFileName(filePath) {
-    return filePath.split(/[/\\]/).pop();
-  }
-
-  // ===== Tab UI =====
-  function renderTabBar() {
-    tabList.innerHTML = '';
-    for (const tab of tabs) {
-      const el = document.createElement('div');
-      el.className = 'tab-item' + (tab.id === activeTabId ? ' active' : '') + (tab.isModified ? ' modified' : '');
-      el.dataset.tabId = tab.id;
-
-      const name = document.createElement('span');
-      name.className = 'tab-name';
-      name.textContent = tab.filePath ? getFileName(tab.filePath) : '未命名';
-      el.appendChild(name);
-
-      const close = document.createElement('button');
-      close.className = 'tab-close';
-      close.innerHTML = '<svg width="10" height="10" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="18" y1="6" x2="6" y2="18"></line><line x1="6" y1="6" x2="18" y2="18"></line></svg>';
-      close.addEventListener('click', (e) => {
-        e.stopPropagation();
-        closeTab(tab.id);
-      });
-      el.appendChild(close);
-
-      el.addEventListener('click', () => switchToTab(tab.id));
-      tabList.appendChild(el);
-    }
-  }
-
-  function updateTitle() {
-    const tab = getActiveTab();
-    if (tab) {
-      const name = tab.filePath ? getFileName(tab.filePath) : '未命名';
-      const mod = tab.isModified ? ' *' : '';
-      document.title = `MarkLite - ${name}${mod}`;
-      statusText.textContent = name;
-    } else {
-      document.title = 'MarkLite';
-      statusText.textContent = '就绪';
-    }
-  }
-
-  // ===== Sidebar Highlight =====
-  // Update sidebar active highlight without re-rendering the entire tree
-  function updateSidebarHighlight() {
-    const tab = getActiveTab();
-    const activePath = tab ? tab.filePath : null;
-
-    // No folder open: manage independent files section
-    if (!currentRootPath) {
-      sidebarTree.innerHTML = '';
-      const indepSection = renderIndependentFiles();
-      if (indepSection) sidebarTree.appendChild(indepSection);
-      return;
-    }
-
-    // Folder is open: re-render independent files section (files may have been added/removed)
-    const oldSection = sidebarTree.querySelector('.independent-files-section');
-    const newSection = renderIndependentFiles();
-    if (oldSection) oldSection.remove();
-    if (newSection) sidebarTree.insertBefore(newSection, sidebarTree.firstChild);
-
-    // Update folder tree items
-    const treeItems = sidebarTree.querySelectorAll('.tree-item:not(.independent-file-item)');
-    treeItems.forEach(item => {
-      const itemPath = item.dataset.path;
-      if (itemPath) {
-        item.classList.toggle('active', itemPath === activePath);
-      }
-    });
-  }
-
-  // ===== Tab Operations =====
-  function getActiveTab() {
-    return tabs.find(t => t.id === activeTabId) || null;
-  }
-
-  function getTabIndex(tabId) {
-    return tabs.findIndex(t => t.id === tabId);
-  }
-
-  // Save current editor state into the active tab
-  function saveCurrentTabState() {
-    const tab = getActiveTab();
-    if (!tab) return;
-    tab.content = editor.value;
-    tab.scrollTop = editor.scrollTop;
-    tab.scrollLeft = editor.scrollLeft;
-    tab.selectionStart = editor.selectionStart;
-    tab.selectionEnd = editor.selectionEnd;
-    tab.previewScrollTop = previewPanel.scrollTop;
-  }
-
-  // Load a tab's state into the editor
-  function loadTabState(tab) {
-    // 使用 execCommand('insertText') 替换内容，保留 undo/redo 历史
-    // setRangeText 会清空 undo 栈，所以此处必须用 execCommand
-    editor.focus();
-    editor.select();
-    const inserted = document.execCommand('insertText', false, tab.content);
-    if (!inserted) {
-      // execCommand 被禁用时的 fallback（会丢失 undo 历史）
-      editor.value = tab.content;
-    }
-    lineCountCache = 0;
-    updateLineNumbers();
-    renderMarkdown(tab.content);
-    updateFileSize();
-    cachePreviewPositions();
-
-    // Restore scroll/selection on next frame
-    requestAnimationFrame(() => {
-      editor.scrollTop = tab.scrollTop;
-      editor.scrollLeft = tab.scrollLeft;
-      lineNumbers.scrollTop = tab.scrollTop;
-      editor.setSelectionRange(tab.selectionStart, tab.selectionEnd);
-      previewPanel.scrollTop = tab.previewScrollTop;
-      updateCursorPosition();
-    });
-
-    // Update modified state
-    setModified(tab.isModified);
-
-    // Notify main process about active file
-    if (typeof window.electronAPI !== 'undefined') {
-      window.electronAPI.tabSwitched(tab.filePath);
-    }
-  }
-
-  function setModified(modified) {
-    const tab = getActiveTab();
-    if (tab) {
-      tab.isModified = modified;
-      // Toggle class directly instead of rebuilding entire tab bar
-      const tabEl = tabList.querySelector(`.tab-item[data-tab-id="${tab.id}"]`);
-      if (tabEl) tabEl.classList.toggle('modified', modified);
-    }
-    updateTitle();
-  }
-
-  // Create a new tab and switch to it
-  function createNewTab(filePath, content) {
-    // Check if file is already open
-    if (filePath) {
-      const existing = tabs.find(t => t.filePath === filePath);
-      if (existing) {
-        switchToTab(existing.id);
-        return existing;
-      }
-    }
-
-    const tab = createTab(filePath, content);
-    tabs.push(tab);
-    switchToTab(tab.id);
-    return tab;
-  }
-
-  // Switch to a specific tab
-  function switchToTab(tabId) {
-    if (tabId === activeTabId) return;
-
-    // Save current state
-    saveCurrentTabState();
-
-    // MRU: record previous tab before switching
-    if (activeTabId) {
-      mruTabStack = mruTabStack.filter(id => id !== activeTabId);
-      mruTabStack.unshift(activeTabId);
-    }
-
-    // Switch
-    activeTabId = tabId;
-    const tab = getActiveTab();
-    if (!tab) return;
-
-    loadTabState(tab);
-    renderTabBar();
-    updateTitle();
-    updateSidebarHighlight();
-    welcomeScreen.classList.add('hidden');
-  }
-
-  // Close a tab
-  function closeTab(tabId) {
-    const index = getTabIndex(tabId);
-    if (index === -1) return;
-
-    const tab = tabs[index];
-
-    // If modified, confirm
-    if (tab.isModified) {
-      const name = tab.filePath ? getFileName(tab.filePath) : '未命名';
-      if (!confirm(`"${name}" 尚未保存，确定要关闭吗？`)) return;
-    }
-
-    // Remove tab
-    tabs.splice(index, 1);
-    // Clean MRU stack
-    mruTabStack = mruTabStack.filter(id => id !== tabId);
-
-    // If we closed the active tab, switch to another
-    if (tabId === activeTabId) {
-      if (tabs.length === 0) {
-        // No tabs left - show welcome screen
-        activeTabId = null;
-        editor.value = '';
-        preview.innerHTML = '';
-        lineNumbers.innerHTML = '';
-        lineCountCache = 0;
-        statusSize.textContent = '';
-        statusSizeDivider.classList.remove('visible');
-        welcomeScreen.classList.remove('hidden');
-        document.title = 'MarkLite';
-        statusText.textContent = '就绪';
-        if (typeof window.electronAPI !== 'undefined') {
-          window.electronAPI.tabSwitched(null);
-        }
-      } else {
-        // Switch to nearest tab
-        const newIndex = Math.min(index, tabs.length - 1);
-        activeTabId = tabs[newIndex].id;
-        loadTabState(tabs[newIndex]);
-      }
-    }
-
-    renderTabBar();
-    updateTitle();
-    updateSidebarHighlight();
-  }
-
-  // ===== File Size Limit =====
-  const MAX_FILE_SIZE = 20 * 1024 * 1024; // 20MB
-
-  // ===== File Operations =====
-  async function handleOpenFile() {
-    if (typeof window.electronAPI !== 'undefined') {
-      const result = await window.electronAPI.openFile();
-      if (result && !result.error) {
-        createNewTab(result.filePath, result.content);
-      }
-    } else {
-      const input = document.createElement('input');
-      input.type = 'file';
-      input.accept = '.md,.markdown,.txt';
-      input.multiple = true;
-      input.onchange = (e) => {
-        Array.from(e.target.files).forEach(file => {
-          const ext = file.name.substring(file.name.lastIndexOf('.')).toLowerCase();
-          if (!['.md', '.markdown', '.txt'].includes(ext)) return;
-          if (file.size > MAX_FILE_SIZE) {
-            alert(`"${file.name}" 过大（${formatBytes(file.size)}），暂不支持超过 20MB 的文件`);
-            return;
-          }
-          const reader = new FileReader();
-          reader.onload = (ev) => {
-            createNewTab(file.name, ev.target.result);
-          };
-          reader.readAsText(file);
-        });
-      };
-      input.click();
-    }
-  }
-
-  async function handleSave() {
-    const tab = getActiveTab();
-    if (!tab) return;
-
-    if (typeof window.electronAPI !== 'undefined') {
-      const result = await window.electronAPI.saveFile({
-        filePath: tab.filePath,
-        content: editor.value
-      });
-      if (result.success) {
-        tab.filePath = result.filePath;
-        tab.content = editor.value;
-        tab.isModified = false;
-        renderTabBar();
-        updateTitle();
-        updateSidebarHighlight();
-        statusText.textContent = '已保存';
-        setTimeout(() => updateTitle(), 2000);
-      }
-    } else {
-      const blob = new Blob([editor.value], { type: 'text/markdown' });
-      const a = document.createElement('a');
-      a.href = URL.createObjectURL(blob);
-      a.download = tab.filePath || 'untitled.md';
-      a.click();
-      setTimeout(() => URL.revokeObjectURL(a.href), 1000);
-      tab.isModified = false;
-      renderTabBar();
-      updateTitle();
-    }
-  }
-
-  async function handleSaveAs() {
-    const tab = getActiveTab();
-    if (!tab) return;
-
-    if (typeof window.electronAPI !== 'undefined') {
-      const result = await window.electronAPI.saveFileAs({ content: editor.value });
-      if (result.success) {
-        tab.filePath = result.filePath;
-        tab.content = editor.value;
-        tab.isModified = false;
-        renderTabBar();
-        updateTitle();
-        updateSidebarHighlight();
-        statusText.textContent = '已保存';
-        setTimeout(() => updateTitle(), 2000);
-      }
-    } else {
-      handleSave();
-    }
-  }
-
-  // ===== View Mode =====
-  function setViewMode(mode) {
-    viewMode = mode;
-    const app = document.getElementById('app');
-    app.classList.remove('mode-editor', 'mode-preview');
-    btnSplit.classList.remove('active');
-    btnEditor.classList.remove('active');
-    btnPreview.classList.remove('active');
-
-    switch (mode) {
-      case 'split':
-        btnSplit.classList.add('active');
-        break;
-      case 'editor':
-        btnEditor.classList.add('active');
-        app.classList.add('mode-editor');
-        break;
-      case 'preview':
-        btnPreview.classList.add('active');
-        app.classList.add('mode-preview');
-        renderMarkdown(editor.value);
-        break;
-    }
-    saveSetting('viewMode', mode);
-  }
-
-  // ===== Resizer =====
-  let isResizing = false;
-
-  function initResizer() {
-    const settings = loadSettings();
-    if (settings.splitRatio) {
-      editorPanel.style.flex = `0 0 ${settings.splitRatio}%`;
-      previewPanel.style.flex = `0 0 ${100 - settings.splitRatio}%`;
-    }
-
-    resizer.addEventListener('mousedown', (e) => {
-      isResizing = true;
-      resizer.classList.add('active');
-      document.body.style.cursor = 'col-resize';
-      document.body.style.userSelect = 'none';
-      e.preventDefault();
-    });
-
-    document.addEventListener('mousemove', (e) => {
-      if (!isResizing) return;
-      const rect = contentWrapper.getBoundingClientRect();
-      const pct = Math.max(20, Math.min(80, ((e.clientX - rect.left) / rect.width) * 100));
-      editorPanel.style.flex = `0 0 ${pct}%`;
-      previewPanel.style.flex = `0 0 ${100 - pct}%`;
-      saveSetting('splitRatio', pct);
-    });
-
-    document.addEventListener('mouseup', () => {
-      if (isResizing) {
-        isResizing = false;
-        resizer.classList.remove('active');
-        document.body.style.cursor = '';
-        document.body.style.userSelect = '';
-      }
-    });
-  }
-
-  // ===== Drag & Drop =====
-  function initDragDrop() {
-    let dragCounter = 0;
-
-    document.addEventListener('dragenter', (e) => {
-      e.preventDefault();
-      e.stopPropagation();
-      dragCounter++;
-      dropOverlay.classList.remove('hidden');
-    });
-
-    document.addEventListener('dragleave', (e) => {
-      e.preventDefault();
-      e.stopPropagation();
-      dragCounter--;
-      if (dragCounter === 0) dropOverlay.classList.add('hidden');
-    });
-
-    document.addEventListener('dragover', (e) => {
-      e.preventDefault();
-      e.stopPropagation();
-    });
-
-    document.addEventListener('drop', async (e) => {
-      e.preventDefault();
-      e.stopPropagation();
-      dragCounter = 0;
-      dropOverlay.classList.add('hidden');
-
-      const files = e.dataTransfer.files;
-      const allowedExts = ['.md', '.markdown', '.txt'];
-      let rejected = 0;
-      for (const file of files) {
-        const filePath = file.path;
-        const ext = filePath ? filePath.substring(filePath.lastIndexOf('.')).toLowerCase() : '';
-        if (!allowedExts.includes(ext)) { rejected++; continue; }
-        // Electron 主进程已有文件大小检查，此处为浏览器模式兜底
-        if (file.size > MAX_FILE_SIZE) {
-          showToast(`"${file.name}" 过大（${formatBytes(file.size)}），暂不支持超过 20MB 的文件`);
-          continue;
-        }
-        if (filePath && typeof window.electronAPI !== 'undefined') {
-          const result = await window.electronAPI.readFile(filePath);
-          if (result.success) {
-            createNewTab(filePath, result.content);
-          }
-        } else {
-          const reader = new FileReader();
-          reader.onload = (ev) => createNewTab(file.name, ev.target.result);
-          reader.readAsText(file);
-        }
-      }
-      if (rejected > 0) {
-        showToast(`仅支持 .md / .markdown / .txt 文件，已忽略 ${rejected} 个文件`);
-      }
-    });
-  }
-
-  // ===== Keyboard Shortcuts =====
-  function initKeyboard() {
-    document.addEventListener('keydown', (e) => {
-      if (e.ctrlKey && e.key === 'o') { e.preventDefault(); handleOpenFile(); }
-      if (e.ctrlKey && e.key === 's' && !e.shiftKey) { e.preventDefault(); handleSave(); }
-      if (e.ctrlKey && e.shiftKey && e.key === 'S') { e.preventDefault(); handleSaveAs(); }
-      if (e.ctrlKey && e.key === '1') { e.preventDefault(); setViewMode('split'); }
-      if (e.ctrlKey && e.key === '2') { e.preventDefault(); setViewMode('editor'); }
-      if (e.ctrlKey && e.key === '3') { e.preventDefault(); setViewMode('preview'); }
-      if (e.ctrlKey && e.key === 't') { e.preventDefault(); createNewTab(null, ''); }
-      if (e.ctrlKey && e.key === 'w') { e.preventDefault(); if (activeTabId) closeTab(activeTabId); }
-      // Ctrl+Tab / Ctrl+Shift+Tab to cycle tabs (MRU order)
-      if (e.ctrlKey && e.key === 'Tab') {
-        e.preventDefault();
-        if (tabs.length > 1) {
-          if (e.shiftKey) {
-            // Ctrl+Shift+Tab: go back in MRU history
-            if (mruTabStack.length > 0) {
-              const targetId = mruTabStack.shift();
-              // Verify target still exists
-              if (tabs.find(t => t.id === targetId)) {
-                switchToTab(targetId);
-              }
-            }
-          } else {
-            // Ctrl+Tab: forward in MRU (just switch to next in array as fallback)
-            const idx = getTabIndex(activeTabId);
-            const next = (idx + 1) % tabs.length;
-            switchToTab(tabs[next].id);
-          }
-        }
-      }
-      // Search & Replace
-      if (e.ctrlKey && e.key === 'f') { e.preventDefault(); openSearch(false); }
-      if (e.ctrlKey && e.key === 'h') { e.preventDefault(); openSearch(true); }
-      if (e.key === 'Escape' && !searchBar.classList.contains('hidden')) { e.preventDefault(); closeSearch(); }
-      if (e.key === 'Enter' && document.activeElement === searchInput) {
-        e.preventDefault();
-        e.shiftKey ? findPrev() : findNext();
-      }
-      if (e.altKey && e.key === 'c') { e.preventDefault(); toggleSearchOption('case'); }
-      if (e.altKey && e.key === 'r') { e.preventDefault(); toggleSearchOption('regex'); }
-      if (e.ctrlKey && e.shiftKey && e.key === 'H') { e.preventDefault(); replaceAll(); }
-      if (e.ctrlKey && e.shiftKey && e.key === 'G') { e.preventDefault(); replaceCurrent(); }
-    });
-  }
-
-  // ===== Tab key support =====
-  function initEditorTab() {
-    editor.addEventListener('keydown', (e) => {
-      if (e.key === 'Tab') {
-        e.preventDefault();
-        // setRangeText 是标准 API，execCommand 已废弃但能保留 undo 历史
-        const start = editor.selectionStart;
-        const end = editor.selectionEnd;
-        if (start !== end) {
-          // 多行选区：批量缩进
-          const lines = editor.value.substring(start, end).split('\n');
-          const indented = lines.map(line => '    ' + line).join('\n');
-          editor.setRangeText(indented, start, end, 'end');
-        } else {
-          // 单光标：插入 4 空格
-          editor.setRangeText('    ', start, end, 'end');
-        }
-        scheduleUpdate();
-      }
-    });
-  }
-
-  // ===== External File Modification =====
-  function initFileWatch() {
-    if (typeof window.electronAPI === 'undefined') return;
-
-    window.electronAPI.onExternalModification((filePath) => {
-      // Only show banner if the modified file is the active tab
-      const tab = getActiveTab();
-      if (tab && tab.filePath === filePath) {
-        modifiedBanner.classList.remove('hidden');
-      }
-    });
-
-    btnReload.addEventListener('click', async () => {
-      const tab = getActiveTab();
-      if (!tab || !tab.filePath) return;
-      const result = await window.electronAPI.reloadFile();
-      if (result.success) {
-        editor.value = result.content;
-        tab.content = result.content;
-        tab.isModified = false;
-        lineCountCache = 0;
-        updateLineNumbers();
-        renderMarkdown(result.content);
-        updateCursorPosition();
-        updateFileSize();
-        cachePreviewPositions();
-        renderTabBar();
-        updateTitle();
-      }
-      modifiedBanner.classList.add('hidden');
-    });
-
-    btnDismiss.addEventListener('click', () => {
-      modifiedBanner.classList.add('hidden');
-    });
-  }
-
-  // ===== Unsaved Changes Warning =====
-  function initUnsavedWarning() {
-    const hasUnsaved = () => tabs.some(t => t.isModified);
-
-    if (typeof window.electronAPI === 'undefined') {
-      window.addEventListener('beforeunload', (e) => {
-        if (hasUnsaved()) { e.preventDefault(); e.returnValue = ''; }
-      });
-      return;
-    }
-
-    window.electronAPI.onConfirmClose(() => {
-      if (!hasUnsaved()) {
-        window.electronAPI.forceClose();
-        return;
-      }
-      const shouldClose = confirm('有文件尚未保存，确定要关闭吗？');
-      if (shouldClose) {
-        window.electronAPI.forceClose();
-      } else {
-        window.electronAPI.cancelClose();
-      }
-    });
-  }
-
-  // ===== Event Listeners =====
-  function initEventListeners() {
-    editor.addEventListener('input', () => {
-      const tab = getActiveTab();
-      if (tab) {
-        tab.isModified = true;
-        tab.content = editor.value;
-        setModified(true);
-      }
-      scheduleUpdate();
-    });
-
-    editor.addEventListener('scroll', () => {
-      syncScroll();
-      // 行号跟随编辑器滚动
-      lineNumbers.scrollTop = editor.scrollTop;
-      // 大文件滚动时重新渲染虚拟行号
-      if (lineCountCache > 2000) {
-        renderVirtualLineNumbers(lineCountCache);
-      }
-    });
-    editor.addEventListener('click', updateCursorPosition);
-    editor.addEventListener('keyup', updateCursorPosition);
-    editor.addEventListener('select', updateCursorPosition);
-
-    btnOpen.addEventListener('click', handleOpenFile);
-    btnSave.addEventListener('click', handleSave);
-    btnSplit.addEventListener('click', () => setViewMode('split'));
-    btnEditor.addEventListener('click', () => setViewMode('editor'));
-    btnPreview.addEventListener('click', () => setViewMode('preview'));
-    btnNewTab.addEventListener('click', () => createNewTab(null, ''));
-
-    btnWelcomeOpen.addEventListener('click', handleOpenFile);
-    btnWelcomeNew.addEventListener('click', () => createNewTab(null, ''));
-
-    if (typeof window.electronAPI !== 'undefined') {
-      // Remove old listeners first to prevent stacking
-      window.electronAPI.removeAllListeners('file:openInTab');
-      window.electronAPI.removeAllListeners('menu:save');
-      window.electronAPI.removeAllListeners('menu:saveAs');
-      window.electronAPI.removeAllListeners('menu:viewMode');
-
-      // Main process sends file to open in a new tab
-      window.electronAPI.onFileOpenInTab((data) => {
-        createNewTab(data.filePath, data.content);
-      });
-
-      window.electronAPI.onMenuSave(() => handleSave());
-      window.electronAPI.onMenuSaveAs(() => handleSaveAs());
-      window.electronAPI.onViewModeChange((mode) => setViewMode(mode));
-    }
-  }
-
-  // ===== Search & Replace =====
-  function openSearch(showReplace) {
-    searchBar.classList.remove('hidden');
-    replaceRow.classList.toggle('hidden', !showReplace);
-    searchInput.focus();
-    // Pre-fill with selected text
-    const selected = editor.value.substring(editor.selectionStart, editor.selectionEnd);
-    if (selected && !selected.includes('\n')) {
-      searchInput.value = selected;
-    }
-    doSearch();
-  }
-
-  function closeSearch() {
-    searchBar.classList.add('hidden');
-    clearHighlights();
-    searchMatches = [];
-    searchIndex = -1;
-    searchCount.textContent = '';
-    editor.focus();
-  }
-
-  function toggleSearchOption(type) {
-    if (type === 'case') {
-      searchCaseSensitive = !searchCaseSensitive;
-      btnCase.classList.toggle('active', searchCaseSensitive);
-    } else {
-      searchUseRegex = !searchUseRegex;
-      btnRegex.classList.toggle('active', searchUseRegex);
-    }
-    doSearch();
-  }
-
-  function doSearch() {
-    clearHighlights();
-    const text = searchInput.value;
-    if (!text) {
-      searchMatches = [];
-      searchIndex = -1;
-      searchCount.textContent = '';
-      return;
-    }
-    searchMatches = findMatches(text);
-    if (searchMatches.length > 0) {
-      // Find the match closest to cursor
-      const cursor = editor.selectionStart;
-      searchIndex = searchMatches.findIndex(m => m.start >= cursor);
-      if (searchIndex === -1) searchIndex = 0;
-      scrollToMatch(searchIndex);
-    } else {
-      searchIndex = -1;
-    }
-    searchCount.textContent = searchMatches.length > 0
-      ? `${searchIndex + 1}/${searchMatches.length}`
-      : '无结果';
-    highlightMatches();
-  }
-
-  function findMatches(text) {
-    const content = editor.value;
-    const matches = [];
-    if (searchUseRegex) {
-      try {
-        const flags = searchCaseSensitive ? 'g' : 'gi';
-        const regex = new RegExp(text, flags);
-        let m;
-        while ((m = regex.exec(content)) !== null) {
-          matches.push({ start: m.index, end: m.index + m[0].length });
-          if (m[0].length === 0) regex.lastIndex++;
-        }
-      } catch { /* invalid regex */ }
-    } else {
-      const haystack = searchCaseSensitive ? content : content.toLowerCase();
-      const needle = searchCaseSensitive ? text : text.toLowerCase();
-      let idx = 0;
-      while ((idx = haystack.indexOf(needle, idx)) !== -1) {
-        matches.push({ start: idx, end: idx + needle.length });
-        idx += needle.length;
-      }
-    }
-    return matches;
-  }
-
-  function highlightMatches() {
-    clearHighlights();
-    if (searchMatches.length === 0) return;
-
-    const content = editor.value;
-    const lineHeight = parseFloat(getComputedStyle(editor).lineHeight) || 20.8;
-    const editorStyle = getComputedStyle(editor);
-    const paddingTop = parseFloat(editorStyle.paddingTop);
-    const paddingLeft = parseFloat(editorStyle.paddingLeft);
-
-    // Compute line starts for fast lookup
-    const lineStarts = [0];
-    for (let i = 0; i < content.length; i++) {
-      if (content.charCodeAt(i) === 10) lineStarts.push(i + 1);
-    }
-
-    function posToXY(pos) {
-      let line = 0;
-      for (let i = 0; i < lineStarts.length; i++) {
-        if (lineStarts[i] > pos) break;
-        line = i;
-      }
-      const col = pos - lineStarts[line];
-      return {
-        top: line * lineHeight + paddingTop,
-        left: col * getCharWidth() + paddingLeft
-      };
-    }
-
-    const overlay = document.createElement('div');
-    overlay.id = 'search-highlights';
-    overlay.style.cssText = 'position:absolute;top:0;left:0;right:0;bottom:0;pointer-events:none;overflow:hidden;z-index:1;';
-    const wrapper = document.getElementById('editor-wrapper');
-    wrapper.style.position = 'relative';
-    wrapper.appendChild(overlay);
-
-    for (let i = 0; i < searchMatches.length; i++) {
-      const m = searchMatches[i];
-      const startPos = posToXY(m.start);
-      const endPos = posToXY(m.end);
-      const isCurrent = i === searchIndex;
-      const div = document.createElement('div');
-      div.className = 'search-hl' + (isCurrent ? ' current' : '');
-      div.style.cssText = `position:absolute;top:${startPos.top}px;left:${startPos.left}px;height:${lineHeight}px;width:${Math.max(endPos.left - startPos.left, 8)}px;`;
-      overlay.appendChild(div);
-    }
-  }
-
-  function clearHighlights() {
-    const old = document.getElementById('search-highlights');
-    if (old) old.remove();
-  }
-
-  function scrollToMatch(index) {
-    if (index < 0 || index >= searchMatches.length) return;
-    searchIndex = index;
-    const m = searchMatches[index];
-    editor.setSelectionRange(m.start, m.end);
-    // Scroll the match into view
-    const lineHeight = parseFloat(getComputedStyle(editor).lineHeight) || 20.8;
-    const content = editor.value;
-    let line = 0;
-    for (let i = 0; i < m.start; i++) {
-      if (content.charCodeAt(i) === 10) line++;
-    }
-    const matchTop = line * lineHeight;
-    const viewTop = editor.scrollTop;
-    const viewBottom = viewTop + editor.clientHeight;
-    if (matchTop < viewTop + 40 || matchTop > viewBottom - 40) {
-      editor.scrollTop = matchTop - editor.clientHeight / 2;
-    }
-    searchCount.textContent = `${index + 1}/${searchMatches.length}`;
-    highlightMatches();
-  }
-
-  function findNext() {
-    if (searchMatches.length === 0) return;
-    scrollToMatch((searchIndex + 1) % searchMatches.length);
-  }
-
-  function findPrev() {
-    if (searchMatches.length === 0) return;
-    scrollToMatch((searchIndex - 1 + searchMatches.length) % searchMatches.length);
-  }
-
-  function replaceCurrent() {
-    if (searchMatches.length === 0 || searchIndex < 0) return;
-    const m = searchMatches[searchIndex];
-    const replacement = replaceInput.value;
-    // Use execCommand to preserve undo history
-    editor.setSelectionRange(m.start, m.end);
-    document.execCommand('insertText', false, replacement);
-    // Re-run search
-    doSearch();
-  }
-
-  function replaceAll() {
-    if (searchMatches.length === 0) return;
-    const replacement = replaceInput.value;
-    // Replace from end to start to preserve positions
-    for (let i = searchMatches.length - 1; i >= 0; i--) {
-      const m = searchMatches[i];
-      editor.setSelectionRange(m.start, m.end);
-      document.execCommand('insertText', false, replacement);
-    }
-    doSearch();
-  }
-
-  // ===== Sidebar (File Tree) =====
-  function initSidebar() {
-    const settings = loadSettings();
-    if (settings.sidebarCollapsed) sidebar.classList.add('collapsed');
-    if (settings.sidebarWidth) {
-      sidebar.style.width = settings.sidebarWidth + 'px';
-    }
-
-    // Sidebar resize handle (#10)
-    const handle = document.createElement('div');
-    handle.className = 'sidebar-resize-handle';
-    sidebar.appendChild(handle);
-    let isSidebarResizing = false;
-    handle.addEventListener('mousedown', (e) => {
-      isSidebarResizing = true;
-      document.body.style.cursor = 'col-resize';
-      document.body.style.userSelect = 'none';
-      e.preventDefault();
-    });
-    document.addEventListener('mousemove', (e) => {
-      if (!isSidebarResizing) return;
-      const newWidth = Math.max(180, Math.min(500, e.clientX));
-      sidebar.style.width = newWidth + 'px';
-      saveSetting('sidebarWidth', newWidth);
-    });
-    document.addEventListener('mouseup', () => {
-      if (isSidebarResizing) {
-        isSidebarResizing = false;
-        document.body.style.cursor = '';
-        document.body.style.userSelect = '';
-      }
-    });
-
-    btnOpenFolder.addEventListener('click', openFolder);
-    if (typeof window.electronAPI !== 'undefined') {
-      let dirRefreshTimer = null;
-      window.electronAPI.onDirChanged(() => {
-        if (!currentRootPath) return;
-        if (dirRefreshTimer) clearTimeout(dirRefreshTimer);
-        dirRefreshTimer = setTimeout(() => refreshTree(), 300);
-      });
-    }
-  }
-
-  async function openFolder() {
-    if (typeof window.electronAPI === 'undefined') return;
-    openFolderDialog();
-  }
-
-  async function openFolderDialog() {
-    if (typeof window.electronAPI !== 'undefined' && window.electronAPI.openFolderDialog) {
-      const result = await window.electronAPI.openFolderDialog();
-      if (result) {
-        loadFolder(result);
-      }
-    }
-  }
-
-  async function loadFolder(dirPath) {
-    if (typeof window.electronAPI === 'undefined') return;
-    currentRootPath = dirPath;
-    const result = await window.electronAPI.readDirTree(dirPath);
-    if (result.success) {
-      renderTree(result.tree, dirPath);
-      sidebar.classList.remove('collapsed');
-      window.electronAPI.watchDir(dirPath);
-    }
-  }
-
-  async function refreshTree() {
-    if (!currentRootPath) return;
-    const result = await window.electronAPI.readDirTree(currentRootPath);
-    if (result.success) {
-      renderTree(result.tree, currentRootPath);
-    }
-  }
-
-  // Track expanded state
-  const expandedDirs = new Set();
-
-  function renderTree(tree, rootPath) {
-    sidebarTree.innerHTML = '';
-    const rootNode = { name: getFileName(rootPath) || rootPath, path: rootPath, type: 'dir', children: tree };
-    expandedDirs.add(rootPath);
-    const fragment = document.createDocumentFragment();
-    buildTreeDOM(fragment, rootNode, 0);
-    sidebarTree.appendChild(fragment);
-  }
-
-  function buildTreeDOM(parent, node, depth) {
-    const item = document.createElement('div');
-    item.className = 'tree-item';
-    item.style.paddingLeft = (8 + depth * 16) + 'px';
-
-    if (node.type === 'dir') {
-      const isExpanded = expandedDirs.has(node.path);
-      const arrow = document.createElement('span');
-      arrow.className = 'tree-arrow' + (isExpanded ? ' expanded' : '');
-      arrow.innerHTML = '<svg width="10" height="10" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5"><polyline points="9 18 15 12 9 6"></polyline></svg>';
-      item.appendChild(arrow);
-
-      const icon = document.createElement('span');
-      icon.className = 'tree-icon';
-      icon.innerHTML = '<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M22 19a2 2 0 0 1-2 2H4a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h5l2 3h9a2 2 0 0 1 2 2z"></path></svg>';
-      item.appendChild(icon);
-
-      const name = document.createElement('span');
-      name.className = 'tree-name';
-      name.textContent = node.name;
-      item.appendChild(name);
-
-      parent.appendChild(item);
-
-      if (isExpanded && node.children) {
-        for (const child of node.children) {
-          buildTreeDOM(parent, child, depth + 1);
-        }
-      }
-
-      item.addEventListener('click', (e) => {
-        e.stopPropagation();
-        if (expandedDirs.has(node.path)) {
-          expandedDirs.delete(node.path);
-        } else {
-          expandedDirs.add(node.path);
-        }
-        renderTree(getTreeData(), currentRootPath);
-      });
-    } else {
-      // Spacer for alignment (no arrow)
-      const spacer = document.createElement('span');
-      spacer.style.width = '16px';
-      spacer.style.flexShrink = '0';
-      item.appendChild(spacer);
-
-      const icon = document.createElement('span');
-      icon.className = 'tree-icon';
-      icon.innerHTML = '<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"></path><polyline points="14 2 14 8 20 8"></polyline></svg>';
-      item.appendChild(icon);
-
-      const name = document.createElement('span');
-      name.className = 'tree-name';
-      name.textContent = node.name;
-      item.appendChild(name);
-
-      // Highlight if this file is open in active tab
-      const tab = getActiveTab();
-      if (tab && tab.filePath === node.path) {
-        item.classList.add('active');
-      }
-      item.dataset.path = node.path;
-
-      parent.appendChild(item);
-
-      item.addEventListener('click', async (e) => {
-        e.stopPropagation();
-        // Check if already open
-        const existing = tabs.find(t => t.filePath === node.path);
-        if (existing) {
-          switchToTab(existing.id);
-        } else {
-          if (typeof window.electronAPI !== 'undefined') {
-            const result = await window.electronAPI.readFile(node.path);
-            if (result.success) {
-              createNewTab(node.path, result.content);
-            }
-          }
-        }
-      });
-    }
-  }
-
-  // Cache the last tree data for re-render
-  let lastTreeData = null;
-
-  function getTreeData() {
-    return lastTreeData || [];
-  }
-
-  // Build list of open files that are NOT inside currentRootPath
-  function getIndependentFiles() {
-    if (!tabs.length) return [];
-    return tabs.filter(t => {
-      if (!t.filePath) return false; // skip unnamed tabs
-      if (!currentRootPath) return true; // no folder open → all files are "independent"
-      // Check if file is inside the current root path
-      return !t.filePath.startsWith(currentRootPath);
-    });
-  }
-
-  function renderIndependentFiles() {
-    const files = getIndependentFiles();
-    if (files.length === 0) return null;
-
-    const section = document.createElement('div');
-    section.className = 'independent-files-section';
-
-    const header = document.createElement('div');
-    header.className = 'independent-files-header';
-    header.textContent = '已打开的文件';
-    section.appendChild(header);
-
-    for (const tab of files) {
-      const item = document.createElement('div');
-      item.className = 'tree-item independent-file-item';
-      item.style.paddingLeft = '8px';
-      item.dataset.path = tab.filePath;
-
-      const icon = document.createElement('span');
-      icon.className = 'tree-icon';
-      icon.innerHTML = '<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"></path><polyline points="14 2 14 8 20 8"></polyline></svg>';
-      item.appendChild(icon);
-
-      const name = document.createElement('span');
-      name.className = 'tree-name';
-      name.textContent = getFileName(tab.filePath);
-      item.appendChild(name);
-
-      // Mark as modified
-      if (tab.isModified) {
-        const dot = document.createElement('span');
-        dot.className = 'independent-modified-dot';
-        dot.textContent = ' •';
-        item.appendChild(dot);
-      }
-
-      // Highlight if active
-      if (tab.id === activeTabId) {
-        item.classList.add('active');
-      }
-
-      item.addEventListener('click', (e) => {
-        e.stopPropagation();
-        switchToTab(tab.id);
-      });
-
-      section.appendChild(item);
-    }
-    return section;
-  }
-
-  // Override renderTree to cache data, add header, and prepend independent files
-  const _originalRenderTree = renderTree;
-  renderTree = function(tree, rootPath) {
-    lastTreeData = tree;
-    _originalRenderTree(tree, rootPath);
-    // Add folder tree header
-    const folderHeader = document.createElement('div');
-    folderHeader.className = 'sidebar-section-header';
-    folderHeader.textContent = '文件夹目录树';
-    sidebarTree.insertBefore(folderHeader, sidebarTree.firstChild);
-    // Prepend independent files section
-    const indepSection = renderIndependentFiles();
-    if (indepSection) {
-      sidebarTree.insertBefore(indepSection, sidebarTree.firstChild);
-    }
-  };
-
-  // ===== Search Bar Init =====
-  function initSearchBar() {
-    searchInput.addEventListener('input', doSearch);
-    btnCase.addEventListener('click', () => toggleSearchOption('case'));
-    btnRegex.addEventListener('click', () => toggleSearchOption('regex'));
-    btnNext.addEventListener('click', findNext);
-    btnPrev.addEventListener('click', findPrev);
-    btnSearchClose.addEventListener('click', closeSearch);
-    btnReplace.addEventListener('click', replaceCurrent);
-    btnReplaceAll.addEventListener('click', replaceAll);
-  }
-
-  // ===== Initialize =====
-  function init() {
-    initMarked();
-    initDarkMode();
-    initResizer();
-    initDragDrop();
-    initKeyboard();
-    initEditorTab();
-    initPreviewLinks();
-    initEventListeners();
-    initFileWatch();
-    initUnsavedWarning();
-    initSidebar();
-    initSearchBar();
-
-    const settings = loadSettings();
-    setViewMode(settings.viewMode || 'split');
-  }
-
-  if (document.readyState === 'loading') {
-    document.addEventListener('DOMContentLoaded', init);
-  } else {
-    init();
-  }
-})();
diff --git a/renderer/search.js b/renderer/search.js
new file mode 100644
index 0000000..385365f
--- /dev/null
+++ b/renderer/search.js
@@ -0,0 +1,158 @@
+// MarkLite — Search & Replace Module
+(function () {
+  'use strict';
+  var ML = window.MarkLite;
+
+  var searchMatches = [];
+  var searchIndex = -1;
+  var searchCaseSensitive = false;
+  var searchUseRegex = false;
+
+  ML.openSearch = function (showReplace) {
+    ML.searchBar.classList.remove('hidden');
+    ML.replaceRow.classList.toggle('hidden', !showReplace);
+    ML.searchInput.focus();
+    var selected = ML.editor.value.substring(ML.editor.selectionStart, ML.editor.selectionEnd);
+    if (selected && !selected.includes('\n')) ML.searchInput.value = selected;
+    doSearch();
+  };
+
+  ML.closeSearch = function () {
+    ML.searchBar.classList.add('hidden');
+    clearHighlights();
+    searchMatches = []; searchIndex = -1;
+    ML.searchCount.textContent = '';
+    ML.editor.focus();
+  };
+
+  ML.toggleSearchOption = function (type) {
+    if (type === 'case') { searchCaseSensitive = !searchCaseSensitive; ML.btnCase.classList.toggle('active', searchCaseSensitive); }
+    else { searchUseRegex = !searchUseRegex; ML.btnRegex.classList.toggle('active', searchUseRegex); }
+    doSearch();
+  };
+
+  function doSearch() {
+    clearHighlights();
+    var text = ML.searchInput.value;
+    if (!text) { searchMatches = []; searchIndex = -1; ML.searchCount.textContent = ''; return; }
+    searchMatches = findMatches(text);
+    if (searchMatches.length > 0) {
+      var cursor = ML.editor.selectionStart;
+      searchIndex = searchMatches.findIndex(function (m) { return m.start >= cursor; });
+      if (searchIndex === -1) searchIndex = 0;
+      scrollToMatch(searchIndex);
+    } else { searchIndex = -1; }
+    ML.searchCount.textContent = searchMatches.length > 0 ? (searchIndex + 1) + '/' + searchMatches.length : '无结果';
+    highlightMatches();
+  }
+
+  function findMatches(text) {
+    var content = ML.editor.value;
+    var matches = [];
+    if (searchUseRegex) {
+      try {
+        var flags = searchCaseSensitive ? 'g' : 'gi';
+        var regex = new RegExp(text, flags);
+        var m;
+        while ((m = regex.exec(content)) !== null) {
+          matches.push({ start: m.index, end: m.index + m[0].length });
+          if (m[0].length === 0) regex.lastIndex++;
+        }
+      } catch (e) { /* invalid regex */ }
+    } else {
+      var haystack = searchCaseSensitive ? content : content.toLowerCase();
+      var needle = searchCaseSensitive ? text : text.toLowerCase();
+      var idx = 0;
+      while ((idx = haystack.indexOf(needle, idx)) !== -1) {
+        matches.push({ start: idx, end: idx + needle.length });
+        idx += needle.length;
+      }
+    }
+    return matches;
+  }
+
+  function highlightMatches() {
+    clearHighlights();
+    if (searchMatches.length === 0) return;
+    var content = ML.editor.value;
+    var lineHeight = parseFloat(getComputedStyle(ML.editor).lineHeight) || 20.8;
+    var editorStyle = getComputedStyle(ML.editor);
+    var paddingTop = parseFloat(editorStyle.paddingTop);
+    var paddingLeft = parseFloat(editorStyle.paddingLeft);
+    var lineStarts = [0];
+    for (var i = 0; i < content.length; i++) { if (content.charCodeAt(i) === 10) lineStarts.push(i + 1); }
+    function posToXY(pos) {
+      var line = 0;
+      for (var _i = 0; _i < lineStarts.length; _i++) { if (lineStarts[_i] > pos) break; line = _i; }
+      return { top: line * lineHeight + paddingTop, left: (pos - lineStarts[line]) * ML.getCharWidth() + paddingLeft };
+    }
+    var overlay = document.createElement('div');
+    overlay.id = 'search-highlights';
+    overlay.style.cssText = 'position:absolute;top:0;left:0;right:0;bottom:0;pointer-events:none;overflow:hidden;z-index:1;';
+    var wrapper = document.getElementById('editor-wrapper');
+    wrapper.style.position = 'relative';
+    wrapper.appendChild(overlay);
+    for (var _i2 = 0; _i2 < searchMatches.length; _i2++) {
+      var m = searchMatches[_i2];
+      var startPos = posToXY(m.start);
+      var endPos = posToXY(m.end);
+      var isCurrent = _i2 === searchIndex;
+      var div = document.createElement('div');
+      div.className = 'search-hl' + (isCurrent ? ' current' : '');
+      div.style.cssText = 'position:absolute;top:' + startPos.top + 'px;left:' + startPos.left + 'px;height:' + lineHeight + 'px;width:' + Math.max(endPos.left - startPos.left, 8) + 'px;';
+      overlay.appendChild(div);
+    }
+  }
+
+  function clearHighlights() { var old = document.getElementById('search-highlights'); if (old) old.remove(); }
+
+  function scrollToMatch(index) {
+    if (index < 0 || index >= searchMatches.length) return;
+    searchIndex = index;
+    var m = searchMatches[index];
+    ML.editor.setSelectionRange(m.start, m.end);
+    var lineHeight = parseFloat(getComputedStyle(ML.editor).lineHeight) || 20.8;
+    var content = ML.editor.value;
+    var line = 0;
+    for (var i = 0; i < m.start; i++) { if (content.charCodeAt(i) === 10) line++; }
+    var matchTop = line * lineHeight;
+    var viewTop = ML.editor.scrollTop;
+    var viewBottom = viewTop + ML.editor.clientHeight;
+    if (matchTop < viewTop + 40 || matchTop > viewBottom - 40) ML.editor.scrollTop = matchTop - ML.editor.clientHeight / 2;
+    ML.searchCount.textContent = (index + 1) + '/' + searchMatches.length;
+    highlightMatches();
+  }
+
+  ML.findNext = function () { if (searchMatches.length === 0) return; scrollToMatch((searchIndex + 1) % searchMatches.length); };
+  ML.findPrev = function () { if (searchMatches.length === 0) return; scrollToMatch((searchIndex - 1 + searchMatches.length) % searchMatches.length); };
+
+  ML.replaceCurrent = function () {
+    if (searchMatches.length === 0 || searchIndex < 0) return;
+    var m = searchMatches[searchIndex];
+    ML.editor.setSelectionRange(m.start, m.end);
+    document.execCommand('insertText', false, ML.replaceInput.value);
+    doSearch();
+  };
+
+  ML.replaceAll = function () {
+    if (searchMatches.length === 0) return;
+    var replacement = ML.replaceInput.value;
+    for (var i = searchMatches.length - 1; i >= 0; i--) {
+      var m = searchMatches[i];
+      ML.editor.setSelectionRange(m.start, m.end);
+      document.execCommand('insertText', false, replacement);
+    }
+    doSearch();
+  };
+
+  ML.initSearchBar = function () {
+    ML.searchInput.addEventListener('input', doSearch);
+    ML.btnCase.addEventListener('click', function () { ML.toggleSearchOption('case'); });
+    ML.btnRegex.addEventListener('click', function () { ML.toggleSearchOption('regex'); });
+    ML.btnNext.addEventListener('click', ML.findNext);
+    ML.btnPrev.addEventListener('click', ML.findPrev);
+    ML.btnSearchClose.addEventListener('click', ML.closeSearch);
+    ML.btnReplace.addEventListener('click', ML.replaceCurrent);
+    ML.btnReplaceAll.addEventListener('click', ML.replaceAll);
+  };
+})();
diff --git a/renderer/sidebar.js b/renderer/sidebar.js
new file mode 100644
index 0000000..4600043
--- /dev/null
+++ b/renderer/sidebar.js
@@ -0,0 +1,208 @@
+// MarkLite — Sidebar Module: file tree, independent files, resize handle
+(function () {
+  'use strict';
+  var ML = window.MarkLite;
+
+  var expandedDirs = new Set();
+  var lastTreeData = null;
+
+  // ===== Sidebar Highlight =====
+  ML.updateSidebarHighlight = function () {
+    var tab = ML.getActiveTab();
+    var activePath = tab ? tab.filePath : null;
+    if (!ML.currentRootPath) {
+      ML.sidebarTree.innerHTML = '';
+      var indep = renderIndependentFiles();
+      if (indep) ML.sidebarTree.appendChild(indep);
+      return;
+    }
+    var oldSection = ML.sidebarTree.querySelector('.independent-files-section');
+    var newSection = renderIndependentFiles();
+    if (oldSection) oldSection.remove();
+    if (newSection) ML.sidebarTree.insertBefore(newSection, ML.sidebarTree.firstChild);
+    var treeItems = ML.sidebarTree.querySelectorAll('.tree-item:not(.independent-file-item)');
+    treeItems.forEach(function (item) {
+      var itemPath = item.dataset.path;
+      if (itemPath) item.classList.toggle('active', itemPath === activePath);
+    });
+  };
+
+  // ===== Independent Files =====
+  function getIndependentFiles() {
+    if (!ML.tabs.length) return [];
+    return ML.tabs.filter(function (t) {
+      if (!t.filePath) return false;
+      if (!ML.currentRootPath) return true;
+      return !t.filePath.startsWith(ML.currentRootPath);
+    });
+  }
+
+  function renderIndependentFiles() {
+    var files = getIndependentFiles();
+    if (files.length === 0) return null;
+    var section = document.createElement('div');
+    section.className = 'independent-files-section';
+    var header = document.createElement('div');
+    header.className = 'independent-files-header';
+    header.textContent = '已打开的文件';
+    section.appendChild(header);
+    files.forEach(function (tab) {
+      var item = document.createElement('div');
+      item.className = 'tree-item independent-file-item';
+      item.style.paddingLeft = '8px';
+      item.dataset.path = tab.filePath;
+      var icon = document.createElement('span');
+      icon.className = 'tree-icon';
+      icon.innerHTML = '<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"></path><polyline points="14 2 14 8 20 8"></polyline></svg>';
+      item.appendChild(icon);
+      var name = document.createElement('span');
+      name.className = 'tree-name';
+      name.textContent = ML.getFileName(tab.filePath);
+      item.appendChild(name);
+      if (tab.isModified) {
+        var dot = document.createElement('span');
+        dot.className = 'independent-modified-dot';
+        dot.textContent = ' •';
+        item.appendChild(dot);
+      }
+      if (tab.id === ML.activeTabId) item.classList.add('active');
+      item.addEventListener('click', function (e) { e.stopPropagation(); ML.switchToTab(tab.id); });
+      section.appendChild(item);
+    });
+    return section;
+  }
+
+  // ===== Folder Operations =====
+  async function openFolderDialog() {
+    if (typeof window.electronAPI !== 'undefined' && window.electronAPI.openFolderDialog) {
+      var result = await window.electronAPI.openFolderDialog();
+      if (result) loadFolder(result);
+    }
+  }
+
+  async function loadFolder(dirPath) {
+    if (typeof window.electronAPI === 'undefined') return;
+    ML.currentRootPath = dirPath;
+    var result = await window.electronAPI.readDirTree(dirPath);
+    if (result.success) {
+      renderTree(result.tree, dirPath);
+      ML.sidebar.classList.remove('collapsed');
+      window.electronAPI.watchDir(dirPath);
+    }
+  }
+
+  async function refreshTree() {
+    if (!ML.currentRootPath) return;
+    var result = await window.electronAPI.readDirTree(ML.currentRootPath);
+    if (result.success) renderTree(result.tree, ML.currentRootPath);
+  }
+
+  // ===== Tree Rendering =====
+  function renderTreeOriginal(tree, rootPath) {
+    ML.sidebarTree.innerHTML = '';
+    var rootNode = { name: ML.getFileName(rootPath) || rootPath, path: rootPath, type: 'dir', children: tree };
+    expandedDirs.add(rootPath);
+    var fragment = document.createDocumentFragment();
+    buildTreeDOM(fragment, rootNode, 0);
+    ML.sidebarTree.appendChild(fragment);
+  }
+
+  function renderTree(tree, rootPath) {
+    lastTreeData = tree;
+    renderTreeOriginal(tree, rootPath);
+    var folderHeader = document.createElement('div');
+    folderHeader.className = 'sidebar-section-header';
+    folderHeader.textContent = '文件夹目录树';
+    ML.sidebarTree.insertBefore(folderHeader, ML.sidebarTree.firstChild);
+    var indepSection = renderIndependentFiles();
+    if (indepSection) ML.sidebarTree.insertBefore(indepSection, ML.sidebarTree.firstChild);
+  }
+
+  function buildTreeDOM(parent, node, depth) {
+    var item = document.createElement('div');
+    item.className = 'tree-item';
+    item.style.paddingLeft = (8 + depth * 16) + 'px';
+    if (node.type === 'dir') {
+      var isExpanded = expandedDirs.has(node.path);
+      var arrow = document.createElement('span');
+      arrow.className = 'tree-arrow' + (isExpanded ? ' expanded' : '');
+      arrow.innerHTML = '<svg width="10" height="10" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5"><polyline points="9 18 15 12 9 6"></polyline></svg>';
+      item.appendChild(arrow);
+      var icon = document.createElement('span');
+      icon.className = 'tree-icon';
+      icon.innerHTML = '<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M22 19a2 2 0 0 1-2 2H4a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h5l2 3h9a2 2 0 0 1 2 2z"></path></svg>';
+      item.appendChild(icon);
+      var name = document.createElement('span');
+      name.className = 'tree-name';
+      name.textContent = node.name;
+      item.appendChild(name);
+      parent.appendChild(item);
+      if (isExpanded && node.children) {
+        node.children.forEach(function (child) { buildTreeDOM(parent, child, depth + 1); });
+      }
+      item.addEventListener('click', function (e) {
+        e.stopPropagation();
+        if (expandedDirs.has(node.path)) expandedDirs.delete(node.path);
+        else expandedDirs.add(node.path);
+        renderTree(lastTreeData || [], ML.currentRootPath);
+      });
+    } else {
+      var spacer = document.createElement('span');
+      spacer.style.width = '16px';
+      spacer.style.flexShrink = '0';
+      item.appendChild(spacer);
+      var fileIcon = document.createElement('span');
+      fileIcon.className = 'tree-icon';
+      fileIcon.innerHTML = '<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"></path><polyline points="14 2 14 8 20 8"></polyline></svg>';
+      item.appendChild(fileIcon);
+      var fileName = document.createElement('span');
+      fileName.className = 'tree-name';
+      fileName.textContent = node.name;
+      item.appendChild(fileName);
+      var tab = ML.getActiveTab();
+      if (tab && tab.filePath === node.path) item.classList.add('active');
+      item.dataset.path = node.path;
+      parent.appendChild(item);
+      item.addEventListener('click', async function (e) {
+        e.stopPropagation();
+        var existing = ML.tabs.find(function (t) { return t.filePath === node.path; });
+        if (existing) { ML.switchToTab(existing.id); }
+        else if (typeof window.electronAPI !== 'undefined') {
+          var result = await window.electronAPI.readFile(node.path);
+          if (result.success) ML.createNewTab(node.path, result.content);
+        }
+      });
+    }
+  }
+
+  // ===== Init =====
+  ML.initSidebar = function () {
+    var settings = ML.loadSettings();
+    if (settings.sidebarCollapsed) ML.sidebar.classList.add('collapsed');
+    if (settings.sidebarWidth) ML.sidebar.style.width = settings.sidebarWidth + 'px';
+
+    // Resize handle
+    var handle = document.createElement('div');
+    handle.className = 'sidebar-resize-handle';
+    ML.sidebar.appendChild(handle);
+    var isResizing = false;
+    handle.addEventListener('mousedown', function (e) { isResizing = true; document.body.style.cursor = 'col-resize'; document.body.style.userSelect = 'none'; e.preventDefault(); });
+    document.addEventListener('mousemove', function (e) {
+      if (!isResizing) return;
+      var newWidth = Math.max(180, Math.min(500, e.clientX));
+      ML.sidebar.style.width = newWidth + 'px';
+      ML.saveSetting('sidebarWidth', newWidth);
+    });
+    document.addEventListener('mouseup', function () { if (isResizing) { isResizing = false; document.body.style.cursor = ''; document.body.style.userSelect = ''; } });
+
+    ML.btnOpenFolder.addEventListener('click', function () { if (typeof window.electronAPI !== 'undefined') openFolderDialog(); });
+    if (typeof window.electronAPI !== 'undefined') {
+      var dirRefreshTimer = null;
+      window.electronAPI.onDirChanged(function () {
+        if (!ML.currentRootPath) return;
+        if (dirRefreshTimer) clearTimeout(dirRefreshTimer);
+        dirRefreshTimer = setTimeout(function () { refreshTree(); }, 300);
+      });
+    }
+  };
+})();
diff --git a/renderer/tabs.js b/renderer/tabs.js
new file mode 100644
index 0000000..b75201b
--- /dev/null
+++ b/renderer/tabs.js
@@ -0,0 +1,156 @@
+// MarkLite — Tabs Module
+(function () {
+  'use strict';
+  var ML = window.MarkLite;
+
+  // ===== Tab State =====
+  ML.tabs = [];
+  ML.activeTabId = null;
+  var tabIdCounter = 0;
+  ML.mruTabStack = [];
+
+  ML.createTab = function (filePath, content) {
+    var id = ++tabIdCounter;
+    return { id: id, filePath: filePath || null, content: content || '', isModified: false, scrollTop: 0, scrollLeft: 0, selectionStart: 0, selectionEnd: 0, previewScrollTop: 0 };
+  };
+
+  ML.getActiveTab = function () { return ML.tabs.find(function (t) { return t.id === ML.activeTabId; }) || null; };
+  ML.getTabIndex = function (tabId) { return ML.tabs.findIndex(function (t) { return t.id === tabId; }); };
+
+  ML.saveCurrentTabState = function () {
+    var tab = ML.getActiveTab();
+    if (!tab) return;
+    tab.content = ML.editor.value;
+    tab.scrollTop = ML.editor.scrollTop;
+    tab.scrollLeft = ML.editor.scrollLeft;
+    tab.selectionStart = ML.editor.selectionStart;
+    tab.selectionEnd = ML.editor.selectionEnd;
+    tab.previewScrollTop = ML.previewPanel.scrollTop;
+  };
+
+  ML.loadTabState = function (tab) {
+    ML.editor.focus(); ML.editor.select();
+    var inserted = document.execCommand('insertText', false, tab.content);
+    if (!inserted) ML.editor.value = tab.content;
+    ML.lineCountCache = 0;
+    ML.updateLineNumbers();
+    ML.renderMarkdown(tab.content);
+    ML.updateFileSize();
+    ML.cachePreviewPositions();
+    requestAnimationFrame(function () {
+      ML.editor.scrollTop = tab.scrollTop;
+      ML.editor.scrollLeft = tab.scrollLeft;
+      ML.lineNumbers.scrollTop = tab.scrollTop;
+      ML.editor.setSelectionRange(tab.selectionStart, tab.selectionEnd);
+      ML.previewPanel.scrollTop = tab.previewScrollTop;
+      ML.updateCursorPosition();
+    });
+    ML.setModified(tab.isModified);
+    if (typeof window.electronAPI !== 'undefined') window.electronAPI.tabSwitched(tab.filePath);
+  };
+
+  ML.setModified = function (modified) {
+    var tab = ML.getActiveTab();
+    if (tab) {
+      tab.isModified = modified;
+      var tabEl = ML.tabList.querySelector('.tab-item[data-tab-id="' + tab.id + '"]');
+      if (tabEl) tabEl.classList.toggle('modified', modified);
+    }
+    ML.updateTitle();
+  };
+
+  ML.createNewTab = function (filePath, content) {
+    if (filePath) {
+      var existing = ML.tabs.find(function (t) { return t.filePath === filePath; });
+      if (existing) { ML.switchToTab(existing.id); return existing; }
+    }
+    var tab = ML.createTab(filePath, content);
+    ML.tabs.push(tab);
+    ML.switchToTab(tab.id);
+    return tab;
+  };
+
+  ML.switchToTab = function (tabId) {
+    if (tabId === ML.activeTabId) return;
+    ML.saveCurrentTabState();
+    if (ML.activeTabId) {
+      ML.mruTabStack = ML.mruTabStack.filter(function (id) { return id !== ML.activeTabId; });
+      ML.mruTabStack.unshift(ML.activeTabId);
+    }
+    ML.activeTabId = tabId;
+    var tab = ML.getActiveTab();
+    if (!tab) return;
+    ML.loadTabState(tab);
+    ML.renderTabBar();
+    ML.updateTitle();
+    ML.updateSidebarHighlight();
+    ML.welcomeScreen.classList.add('hidden');
+  };
+
+  ML.closeTab = function (tabId) {
+    var index = ML.getTabIndex(tabId);
+    if (index === -1) return;
+    var tab = ML.tabs[index];
+    if (tab.isModified) {
+      var name = tab.filePath ? ML.getFileName(tab.filePath) : '未命名';
+      if (!confirm('"' + name + '" 尚未保存，确定要关闭吗？')) return;
+    }
+    ML.tabs.splice(index, 1);
+    ML.mruTabStack = ML.mruTabStack.filter(function (id) { return id !== tabId; });
+    if (tabId === ML.activeTabId) {
+      if (ML.tabs.length === 0) {
+        ML.activeTabId = null;
+        ML.editor.value = '';
+        ML.preview.innerHTML = '';
+        ML.lineNumbers.innerHTML = '';
+        ML.lineCountCache = 0;
+        ML.statusSize.textContent = '';
+        ML.statusSizeDivider.classList.remove('visible');
+        ML.welcomeScreen.classList.remove('hidden');
+        document.title = 'MarkLite';
+        ML.statusText.textContent = '就绪';
+        if (typeof window.electronAPI !== 'undefined') window.electronAPI.tabSwitched(null);
+      } else {
+        var newIndex = Math.min(index, ML.tabs.length - 1);
+        ML.activeTabId = ML.tabs[newIndex].id;
+        ML.loadTabState(ML.tabs[newIndex]);
+      }
+    }
+    ML.renderTabBar();
+    ML.updateTitle();
+    ML.updateSidebarHighlight();
+  };
+
+  ML.renderTabBar = function () {
+    ML.tabList.innerHTML = '';
+    ML.tabs.forEach(function (tab) {
+      var el = document.createElement('div');
+      el.className = 'tab-item' + (tab.id === ML.activeTabId ? ' active' : '') + (tab.isModified ? ' modified' : '');
+      el.dataset.tabId = tab.id;
+      var name = document.createElement('span');
+      name.className = 'tab-name';
+      name.textContent = tab.filePath ? ML.getFileName(tab.filePath) : '未命名';
+      el.appendChild(name);
+      var close = document.createElement('button');
+      close.className = 'tab-close';
+      close.innerHTML = '<svg width="10" height="10" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="18" y1="6" x2="6" y2="18"></line><line x1="6" y1="6" x2="18" y2="18"></line></svg>';
+      close.addEventListener('click', function (e) { e.stopPropagation(); ML.closeTab(tab.id); });
+      el.appendChild(close);
+      el.addEventListener('click', function () { ML.switchToTab(tab.id); });
+      ML.tabList.appendChild(el);
+    });
+  };
+
+  ML.updateTitle = function () {
+    var tab = ML.getActiveTab();
+    if (tab) {
+      var name = tab.filePath ? ML.getFileName(tab.filePath) : '未命名';
+      var mod = tab.isModified ? ' *' : '';
+      document.title = 'MarkLite - ' + name + mod;
+      ML.statusText.textContent = name;
+    } else {
+      document.title = 'MarkLite';
+      ML.statusText.textContent = '就绪';
+    }
+  };
+})();