diff --git a/src/main/file-system.ts b/src/main/file-system.ts
index 04b6150..9148729 100644
--- a/src/main/file-system.ts
+++ b/src/main/file-system.ts
@@ -1,5 +1,7 @@
-import { readFile, stat, writeFile, readdir } from 'fs/promises'
-import { join, extname } from 'path'
+import { readFile, stat, writeFile, readdir, rename } from 'fs/promises'
+import { join, extname, basename } from 'path'
+import { tmpdir } from 'os'
+import type { ReadFileResult, SaveFileResult, FileNode } from '../shared/types'
 
 const MAX_FILE_SIZE = 20 * 1024 * 1024 // 20MB
 const ALLOWED_EXTENSIONS = new Set(['.md', '.markdown', '.txt'])
@@ -8,14 +10,8 @@ const SKIP_DIRS = new Set([
   '.next', '.nuxt', '__pycache__', '.DS_Store'
 ])
 
-export interface FileNode {
-  name: string
-  path: string
-  type: 'file' | 'dir'
-  children?: FileNode[]
-}
-
-export async function readFileContent(filePath: string): Promise<{ success: boolean; content?: string; error?: string }> {
+// L-09: 使用 shared 类型
+export async function readFileContent(filePath: string): Promise<ReadFileResult> {
   try {
     const fileStat = await stat(filePath)
     if (fileStat.size > MAX_FILE_SIZE) {
@@ -30,17 +26,30 @@ export async function readFileContent(filePath: string): Promise<{ success: bool
   }
 }
 
-export async function saveFileContent(filePath: string, content: string): Promise<{ success: boolean; filePath?: string; error?: string }> {
+// M-06: 原子写入（write-to-temp-then-rename）
+export async function saveFileContent(filePath: string, content: string): Promise<SaveFileResult> {
   try {
-    await writeFile(filePath, content, 'utf-8')
+    const dir = require('path').dirname(filePath)
+    const tmpFile = join(tmpdir(), `marklite-${Date.now()}-${basename(filePath)}`)
+    await writeFile(tmpFile, content, 'utf-8')
+    await rename(tmpFile, filePath)
     return { success: true, filePath }
   } catch (err) {
     return { success: false, error: (err as Error).message }
   }
 }
 
-export async function buildDirTree(dirPath: string): Promise<FileNode[]> {
-  const entries = await readdir(dirPath, { withFileTypes: true })
+// M-05: 添加递归深度限制 + 每个 entry 错误边界
+export async function buildDirTree(dirPath: string, depth = 0, maxDepth = 10): Promise<FileNode[]> {
+  if (depth > maxDepth) return []
+
+  let entries
+  try {
+    entries = await readdir(dirPath, { withFileTypes: true })
+  } catch {
+    return [] // L-10: 权限错误时返回空数组而非抛异常
+  }
+
   entries.sort((a, b) => {
     if (a.isDirectory() && !b.isDirectory()) return -1
     if (!a.isDirectory() && b.isDirectory()) return 1
@@ -54,7 +63,7 @@ export async function buildDirTree(dirPath: string): Promise<FileNode[]> {
 
     const childPath = join(dirPath, entry.name)
     if (entry.isDirectory()) {
-      const subChildren = await buildDirTree(childPath)
+      const subChildren = await buildDirTree(childPath, depth + 1, maxDepth)
       if (subChildren.length > 0) {
         children.push({ name: entry.name, path: childPath, type: 'dir', children: subChildren })
       }
diff --git a/src/main/file-watcher.ts b/src/main/file-watcher.ts
index 6647f8a..1c752b1 100644
--- a/src/main/file-watcher.ts
+++ b/src/main/file-watcher.ts
@@ -22,6 +22,11 @@ export class FileWatcher {
           }
         }
       })
+      // M-04: 监听 error 事件，文件被删除时清理状态
+      this.watcher.on('error', () => {
+        this.currentPath = null
+        this.watcher = null
+      })
     } catch {
       // silently ignore
     }
@@ -32,6 +37,7 @@ export class FileWatcher {
       this.watcher.close()
       this.watcher = null
     }
+    this.currentPath = null
   }
 
   getCurrentPath(): string | null {
@@ -60,10 +66,19 @@ export class SidebarWatcher {
         if (win && !win.isDestroyed()) {
           if (this.refreshTimer) clearTimeout(this.refreshTimer)
           this.refreshTimer = setTimeout(() => {
-            win.webContents.send('sidebar:dirChanged')
+            // M-03: 延迟后再次检查窗口状态
+            const w = this.getMainWindow()
+            if (w && !w.isDestroyed()) {
+              w.webContents.send('sidebar:dirChanged')
+            }
           }, 300)
         }
       })
+      // M-04: 监听 error 事件
+      this.watcher.on('error', () => {
+        this.watcher = null
+        this.watchPath = null
+      })
     } catch {
       // silently ignore
     }
diff --git a/src/main/index.ts b/src/main/index.ts
index 3e6dbc3..fa8f9ba 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -19,12 +19,14 @@ const sidebarWatcher = new SidebarWatcher(() => mainWindow)
 function openFileInTab(filePath: string): void {
   if (!mainWindow || mainWindow.isDestroyed()) return
   readFileContent(filePath).then(result => {
-    if (result.success) {
+    if (result.success && mainWindow && !mainWindow.isDestroyed()) {
       state.activeFilePath = filePath
       fileWatcher.start(filePath)
-      mainWindow!.setTitle(`MarkLite - ${filePath.split(/[/\\]/).pop()}`)
-      mainWindow!.webContents.send('file:openInTab', { filePath, content: result.content })
+      mainWindow.setTitle(`MarkLite - ${filePath.split(/[/\\]/).pop()}`)
+      mainWindow.webContents.send('file:openInTab', { filePath, content: result.content })
     }
+  }).catch((err) => {
+    console.error('openFileInTab failed:', err)
   })
 }
 
@@ -70,24 +72,12 @@ if (!lockOk) {
     })
   }
 
-  app.whenReady().then(() => {
-    app.on('open-file', (event, filePath) => {
-      event.preventDefault()
-      if (mainWindow && !mainWindow.isDestroyed() && mainWindow.webContents.isLoading()) {
-        state.pendingFilePath = filePath
-      } else if (mainWindow && !mainWindow.isDestroyed()) {
-        openFileInTab(filePath)
-      } else {
-        state.pendingFilePath = filePath
-      }
-    })
-
+  // B-07: 完整的窗口初始化逻辑（activate 复用）
+  function initWindow(): void {
     mainWindow = createWindow()
 
-    // 注册 IPC 处理器
     registerIpcHandlers(() => mainWindow, fileWatcher, sidebarWatcher, state)
 
-    // 加载渲染进程页面
     if (process.env.ELECTRON_RENDERER_URL) {
       mainWindow.loadURL(process.env.ELECTRON_RENDERER_URL)
     } else {
@@ -108,6 +98,21 @@ if (!lockOk) {
       sidebarWatcher.stop()
       mainWindow = null
     })
+  }
+
+  app.whenReady().then(() => {
+    app.on('open-file', (event, filePath) => {
+      event.preventDefault()
+      if (mainWindow && !mainWindow.isDestroyed() && mainWindow.webContents.isLoading()) {
+        state.pendingFilePath = filePath
+      } else if (mainWindow && !mainWindow.isDestroyed()) {
+        openFileInTab(filePath)
+      } else {
+        state.pendingFilePath = filePath
+      }
+    })
+
+    initWindow()
 
     // 命令行文件
     const cmdFile = getFilePathFromArgs(process.argv)
@@ -120,10 +125,10 @@ if (!lockOk) {
     if (process.platform !== 'darwin') app.quit()
   })
 
+  // B-07: macOS activate 完整重建窗口
   app.on('activate', () => {
     if (BrowserWindow.getAllWindows().length === 0) {
-      mainWindow = createWindow()
-      setupCloseHandler()
+      initWindow()
     }
   })
 }
diff --git a/src/main/ipc-handlers.ts b/src/main/ipc-handlers.ts
index d17efe6..8a1d959 100644
--- a/src/main/ipc-handlers.ts
+++ b/src/main/ipc-handlers.ts
@@ -9,7 +9,7 @@ export function registerIpcHandlers(
   getMainWindow: () => BrowserWindow | null,
   fileWatcher: FileWatcher,
   sidebarWatcher: SidebarWatcher,
-  state: { activeFilePath: string | null; pendingFilePath: string | null }
+  state: { activeFilePath: string | null; pendingFilePath: string | null; isClosing: boolean; closeTimeout: NodeJS.Timeout | null }
 ): void {
   // 打开文件对话框
   ipcMain.handle(IPC_CHANNELS.DIALOG_OPEN_FILE, async () => {
@@ -67,7 +67,9 @@ export function registerIpcHandlers(
           filters: [{ name: 'Markdown 文件', extensions: ['md'] }]
         })
         if (!saveResult.canceled) {
+          fileWatcher.setSelfWriting(true)
           const result = await saveFileContent(saveResult.filePath, data.content)
+          fileWatcher.setSelfWriting(false)
           if (result.success) {
             state.activeFilePath = saveResult.filePath
             fileWatcher.start(saveResult.filePath)
@@ -177,7 +179,12 @@ export function registerIpcHandlers(
     }
   })
 
+  // B-01: 重置关闭状态 + 清除超时定时器
   ipcMain.handle(IPC_CHANNELS.WINDOW_CANCEL_CLOSE, () => {
-    // 重置关闭状态
+    state.isClosing = false
+    if (state.closeTimeout) {
+      clearTimeout(state.closeTimeout)
+      state.closeTimeout = null
+    }
   })
 }
diff --git a/src/main/window-manager.ts b/src/main/window-manager.ts
index 32708d5..5d12774 100644
--- a/src/main/window-manager.ts
+++ b/src/main/window-manager.ts
@@ -1,5 +1,6 @@
 import { BrowserWindow, app } from 'electron'
 import { join } from 'path'
+import { existsSync, statSync } from 'fs'
 
 export function createWindow(): BrowserWindow {
   const mainWindow = new BrowserWindow({
@@ -43,13 +44,16 @@ export function setupSingleInstanceLock(
   return true
 }
 
+// L-08: 使用静态导入 + 验证是文件而非目录
 export function getFilePathFromArgs(args: string[]): string | null {
   for (let i = 1; i < args.length; i++) {
     const arg = args[i]
     if (!arg.startsWith('--') && !arg.startsWith('-')) {
       try {
-        const fs = require('fs')
-        if (fs.existsSync(arg)) return arg
+        if (existsSync(arg)) {
+          const s = statSync(arg)
+          if (s.isFile()) return arg
+        }
       } catch {
         // ignore
       }
diff --git a/src/preload/index.ts b/src/preload/index.ts
index 5a5caa7..48ad9e9 100644
--- a/src/preload/index.ts
+++ b/src/preload/index.ts
@@ -1,5 +1,16 @@
 import { contextBridge, ipcRenderer, shell } from 'electron'
 
+// M-01: 限制 removeAllListeners 只能操作白名单通道
+const ALLOWED_REMOVE_CHANNELS = new Set([
+  'file:openInTab',
+  'menu:save',
+  'menu:saveAs',
+  'menu:viewMode',
+  'file:externallyModified',
+  'sidebar:dirChanged',
+  'window:confirmClose'
+])
+
 contextBridge.exposeInMainWorld('electronAPI', {
   // File operations
   openFile: () => ipcRenderer.invoke('dialog:openFile'),
@@ -42,6 +53,10 @@ contextBridge.exposeInMainWorld('electronAPI', {
   onConfirmClose: (callback: () => void) =>
     ipcRenderer.on('window:confirmClose', () => callback()),
 
-  // Remove listeners
-  removeAllListeners: (channel: string) => ipcRenderer.removeAllListeners(channel)
+  // M-01: 只允许移除白名单通道的监听器
+  removeAllListeners: (channel: string) => {
+    if (ALLOWED_REMOVE_CHANNELS.has(channel)) {
+      ipcRenderer.removeAllListeners(channel)
+    }
+  }
 })
diff --git a/src/renderer/App.tsx b/src/renderer/App.tsx
index 06a978c..888aed9 100644
--- a/src/renderer/App.tsx
+++ b/src/renderer/App.tsx
@@ -113,19 +113,32 @@ export default function App() {
     saveViewMode(mode)
   }, [saveViewMode])
 
-  // 主进程事件
+  // M-11: 主进程事件注册（使用 ref 保持最新回调引用 + cleanup 清理）
+  const handleSaveRef = useRef(handleSave)
+  const handleSaveAsRef = useRef(handleSaveAs)
+  handleSaveRef.current = handleSave
+  handleSaveAsRef.current = handleSaveAs
+
   useEffect(() => {
     if (!window.electronAPI) return
-    window.electronAPI.removeAllListeners('file:openInTab')
-    window.electronAPI.removeAllListeners('menu:save')
-    window.electronAPI.removeAllListeners('menu:saveAs')
+    const api = window.electronAPI
 
-    window.electronAPI.onFileOpenInTab((data: { filePath: string; content: string }) => {
+    const onOpen = (data: { filePath: string; content: string }) => {
       createTab(data.filePath, data.content)
-    })
-    window.electronAPI.onMenuSave(() => handleSave())
-    window.electronAPI.onMenuSaveAs(() => handleSaveAs())
-  }, [createTab, handleSave, handleSaveAs])
+    }
+    const onSave = () => handleSaveRef.current()
+    const onSaveAs = () => handleSaveAsRef.current()
+
+    api.onFileOpenInTab(onOpen)
+    api.onMenuSave(onSave)
+    api.onMenuSaveAs(onSaveAs)
+
+    return () => {
+      api.removeAllListeners('file:openInTab')
+      api.removeAllListeners('menu:save')
+      api.removeAllListeners('menu:saveAs')
+    }
+  }, [createTab])
 
   const activeTab = getActiveTab()
   const hasTabs = tabs.length > 0
@@ -183,7 +196,7 @@ export default function App() {
                   <Editor />
                 </div>
               )}
-              {viewMode !== 'editor' && <div id="resizer" />}
+              {viewMode !== 'editor' && <Resizer onResize={saveSplitRatio} />}
               {viewMode !== 'editor' && (
                 <div id="preview-panel" style={previewStyle}>
                   <Preview />
@@ -206,3 +219,42 @@ export default function App() {
     </div>
   )
 }
+
+// B-08: 分屏调节器组件
+function Resizer({ onResize }: { onResize: (ratio: number) => void }) {
+  const handleMouseDown = useCallback((e: React.MouseEvent) => {
+    e.preventDefault()
+    document.body.style.cursor = 'col-resize'
+    document.body.style.userSelect = 'none'
+
+    const handleMouseMove = (ev: MouseEvent) => {
+      const wrapper = document.getElementById('content-wrapper')
+      if (!wrapper) return
+      const rect = wrapper.getBoundingClientRect()
+      const pct = Math.max(20, Math.min(80, ((ev.clientX - rect.left) / rect.width) * 100))
+      const editorPanel = document.getElementById('editor-panel')
+      const previewPanel = document.getElementById('preview-panel')
+      if (editorPanel) editorPanel.style.flex = `0 0 ${pct}%`
+      if (previewPanel) previewPanel.style.flex = `0 0 ${100 - pct}%`
+    }
+
+    const handleMouseUp = (ev: MouseEvent) => {
+      document.removeEventListener('mousemove', handleMouseMove)
+      document.removeEventListener('mouseup', handleMouseUp)
+      document.body.style.cursor = ''
+      document.body.style.userSelect = ''
+      // 保存最终比例
+      const wrapper = document.getElementById('content-wrapper')
+      if (wrapper) {
+        const rect = wrapper.getBoundingClientRect()
+        const pct = Math.max(20, Math.min(80, ((ev.clientX - rect.left) / rect.width) * 100))
+        onResize(pct)
+      }
+    }
+
+    document.addEventListener('mousemove', handleMouseMove)
+    document.addEventListener('mouseup', handleMouseUp)
+  }, [onResize])
+
+  return <div id="resizer" onMouseDown={handleMouseDown} />
+}
diff --git a/src/renderer/components/DropOverlay/DropOverlay.tsx b/src/renderer/components/DropOverlay/DropOverlay.tsx
index cf35be9..231f263 100644
--- a/src/renderer/components/DropOverlay/DropOverlay.tsx
+++ b/src/renderer/components/DropOverlay/DropOverlay.tsx
@@ -1,29 +1,18 @@
 import React, { useState, useEffect } from 'react'
 
 export function DropOverlay() {
-  const [isVisible, setIsVisible] = useState(false)
+  // L-11: 简化为单一状态
   const [dragCounter, setDragCounter] = useState(0)
 
   useEffect(() => {
     const handleDragEnter = (e: DragEvent) => {
       e.preventDefault()
-      setDragCounter(prev => {
-        const next = prev + 1
-        if (next > 0) setIsVisible(true)
-        return next
-      })
+      setDragCounter(prev => prev + 1)
     }
 
     const handleDragLeave = (e: DragEvent) => {
       e.preventDefault()
-      setDragCounter(prev => {
-        const next = prev - 1
-        if (next <= 0) {
-          setIsVisible(false)
-          return 0
-        }
-        return next
-      })
+      setDragCounter(prev => Math.max(0, prev - 1))
     }
 
     const handleDragOver = (e: DragEvent) => {
@@ -32,7 +21,6 @@ export function DropOverlay() {
 
     const handleDrop = () => {
       setDragCounter(0)
-      setIsVisible(false)
     }
 
     document.addEventListener('dragenter', handleDragEnter)
@@ -48,7 +36,7 @@ export function DropOverlay() {
     }
   }, [])
 
-  if (!isVisible) return null
+  if (dragCounter <= 0) return null
 
   return (
     <div id="drop-overlay">
diff --git a/src/renderer/components/Editor/Editor.tsx b/src/renderer/components/Editor/Editor.tsx
index 758fd27..58bc829 100644
--- a/src/renderer/components/Editor/Editor.tsx
+++ b/src/renderer/components/Editor/Editor.tsx
@@ -1,9 +1,6 @@
 import React, { useEffect, useRef, useCallback, useState } from 'react'
 import { useTabStore } from '../../stores/tabStore'
-import { useEditorStore } from '../../stores/editorStore'
 import { useSearchStore } from '../../stores/searchStore'
-import { findMatches, buildLineStarts, getLineNumber } from '../../lib/searchEngine'
-import type { SearchMatch } from '../../types/search'
 
 export function Editor() {
   const textareaRef = useRef<HTMLTextAreaElement>(null)
@@ -15,7 +12,10 @@ export function Editor() {
   const updateTabContent = useTabStore(s => s.updateTabContent)
   const setModified = useTabStore(s => s.setModified)
 
-  const searchStore = useSearchStore()
+  // L-13: 只选择需要的字段，避免整个 store 变化触发重渲染
+  const searchIsVisible = useSearchStore(s => s.isVisible)
+  const searchFindNext = useSearchStore(s => s.findNext)
+  const searchFindPrev = useSearchStore(s => s.findPrev)
 
   const [lineCount, setLineCount] = useState(1)
   const [cursorPos, setCursorPos] = useState({ line: 1, col: 1 })
@@ -145,15 +145,15 @@ export function Editor() {
     }
 
     // 搜索导航
-    if (e.key === 'Enter' && searchStore.isVisible) {
+    if (e.key === 'Enter' && searchIsVisible) {
       e.preventDefault()
       if (e.shiftKey) {
-        searchStore.findPrev()
+        searchFindPrev()
       } else {
-        searchStore.findNext()
+        searchFindNext()
       }
     }
-  }, [searchStore])
+  }, [searchIsVisible, searchFindNext, searchFindPrev])
 
   // 渲染行号
   const renderLineNumbers = () => {
diff --git a/src/renderer/components/Preview/Preview.tsx b/src/renderer/components/Preview/Preview.tsx
index 00b7991..d637406 100644
--- a/src/renderer/components/Preview/Preview.tsx
+++ b/src/renderer/components/Preview/Preview.tsx
@@ -5,38 +5,27 @@ import { renderMarkdown } from '../../lib/markdown'
 export function Preview() {
   const [html, setHtml] = useState('')
   const previewRef = useRef<HTMLDivElement>(null)
-  const getActiveTab = useTabStore(s => s.getActiveTab)
-  const activeTabId = useTabStore(s => s.activeTabId)
+  const requestIdRef = useRef(0)
 
-  // 渲染 Markdown
+  const activeTabId = useTabStore(s => s.activeTabId)
+  const tabs = useTabStore(s => s.tabs)
+  const activeTab = tabs.find(t => t.id === activeTabId) ?? null
+
+  // B-03 + M-07: 响应式渲染（无轮询，无竞态）
   useEffect(() => {
-    const tab = getActiveTab()
-    if (!tab) {
+    if (!activeTab) {
       setHtml('')
       return
     }
 
-    let cancelled = false
-    renderMarkdown(tab.content).then(result => {
-      if (!cancelled) {
+    const requestId = ++requestIdRef.current
+    renderMarkdown(activeTab.content).then(result => {
+      // M-07: 只有当 requestId 仍为最新时才更新
+      if (requestId === requestIdRef.current) {
         setHtml(result)
       }
     })
-
-    return () => { cancelled = true }
-  }, [activeTabId, getActiveTab])
-
-  // 监听编辑器内容变化
-  useEffect(() => {
-    const timer = setInterval(() => {
-      const tab = getActiveTab()
-      if (!tab) return
-      renderMarkdown(tab.content).then(result => {
-        setHtml(result)
-      })
-    }, 300)
-    return () => clearInterval(timer)
-  }, [getActiveTab])
+  }, [activeTabId, activeTab?.content])
 
   // 拦截链接点击
   const handleClick = useCallback((e: React.MouseEvent) => {
diff --git a/src/renderer/components/SearchBar/SearchBar.tsx b/src/renderer/components/SearchBar/SearchBar.tsx
index cec2669..df78e9a 100644
--- a/src/renderer/components/SearchBar/SearchBar.tsx
+++ b/src/renderer/components/SearchBar/SearchBar.tsx
@@ -54,18 +54,15 @@ export function SearchBar() {
     doSearch(searchText)
   }, [getActiveTab, matches, currentIndex, replaceText, searchText, doSearch])
 
-  // 全部替换
+  // B-02: 全部替换（从后向前逐个替换）
   const handleReplaceAll = useCallback(() => {
     const tab = getActiveTab()
     if (!tab || matches.length === 0) return
-    let result = ''
-    let lastEnd = 0
+    let result = tab.content
     for (let i = matches.length - 1; i >= 0; i--) {
       const m = matches[i]
-      result = tab.content.substring(lastEnd, m.start) + replaceText + result
-      lastEnd = m.end
+      result = result.substring(0, m.start) + replaceText + result.substring(m.end)
     }
-    result = tab.content.substring(0, matches[0].start) + result
     useTabStore.getState().updateTabContent(tab.id, result)
     doSearch(searchText)
   }, [getActiveTab, matches, replaceText, searchText, doSearch])
diff --git a/src/renderer/components/Sidebar/Sidebar.tsx b/src/renderer/components/Sidebar/Sidebar.tsx
index 9825bbe..a701146 100644
--- a/src/renderer/components/Sidebar/Sidebar.tsx
+++ b/src/renderer/components/Sidebar/Sidebar.tsx
@@ -73,7 +73,18 @@ export function Sidebar() {
     }
   }, [isResizing])
 
-  // 独立文件（不在当前文件夹内的已打开文件）
+  // L-12: 提取为 useCallback 避免每次渲染重建
+  const handleFileClick = useCallback(async (path: string) => {
+    const existing = tabs.find(t => t.filePath === path)
+    if (existing) {
+      switchToTab(existing.id)
+    } else if (window.electronAPI) {
+      const result = await window.electronAPI.readFile(path)
+      if (result.success && result.content) {
+        createTab(path, result.content)
+      }
+    }
+  }, [tabs, switchToTab, createTab])
   const independentFiles = tabs.filter(t => {
     if (!t.filePath) return false
     if (!rootPath) return true
@@ -128,17 +139,7 @@ export function Sidebar() {
               expandedDirs={expandedDirs}
               toggleDir={toggleDir}
               activeTabId={activeTabId}
-              onFileClick={async (path) => {
-                const existing = tabs.find(t => t.filePath === path)
-                if (existing) {
-                  switchToTab(existing.id)
-                } else if (window.electronAPI) {
-                  const result = await window.electronAPI.readFile(path)
-                  if (result.success && result.content) {
-                    createTab(path, result.content)
-                  }
-                }
-              }}
+              onFileClick={handleFileClick}
             />
           </>
         )}
diff --git a/src/renderer/components/StatusBar/StatusBar.tsx b/src/renderer/components/StatusBar/StatusBar.tsx
index 644c0df..c4880ec 100644
--- a/src/renderer/components/StatusBar/StatusBar.tsx
+++ b/src/renderer/components/StatusBar/StatusBar.tsx
@@ -3,8 +3,10 @@ import { useTabStore } from '../../stores/tabStore'
 import { getFileName } from '../../lib/fileUtils'
 
 export function StatusBar() {
-  const getActiveTab = useTabStore(s => s.getActiveTab)
-  const tab = getActiveTab()
+  // B-04: 直接选择数据而非函数引用，确保响应式更新
+  const tabs = useTabStore(s => s.tabs)
+  const activeTabId = useTabStore(s => s.activeTabId)
+  const tab = tabs.find(t => t.id === activeTabId) ?? null
 
   return (
     <div id="statusbar">
diff --git a/src/renderer/db/recentFilesRepository.ts b/src/renderer/db/recentFilesRepository.ts
index 81408fd..bc2a881 100644
--- a/src/renderer/db/recentFilesRepository.ts
+++ b/src/renderer/db/recentFilesRepository.ts
@@ -8,6 +8,12 @@ export const recentFilesRepository = {
     } else {
       await db.recentFiles.add({ filePath, lastOpened: Date.now() })
     }
+    // L-06: 清理超过 50 条的旧记录
+    const all = await db.recentFiles.orderBy('lastOpened').reverse().toArray()
+    if (all.length > 50) {
+      const toDelete = all.slice(50)
+      await db.recentFiles.bulkDelete(toDelete.map(f => f.id!))
+    }
   },
 
   async getAll(limit = 20): Promise<string[]> {
diff --git a/src/renderer/db/settingsRepository.ts b/src/renderer/db/settingsRepository.ts
index 47ddc6c..51dbcea 100644
--- a/src/renderer/db/settingsRepository.ts
+++ b/src/renderer/db/settingsRepository.ts
@@ -7,11 +7,11 @@ export const settingsRepository = {
       const record = await db.settings.get('default')
       if (record) {
         return {
-          darkMode: record.darkMode,
-          viewMode: record.viewMode,
-          splitRatio: record.splitRatio,
-          sidebarCollapsed: record.sidebarCollapsed,
-          sidebarWidth: record.sidebarWidth
+          darkMode: record.darkMode ?? DEFAULT_SETTINGS.darkMode,
+          viewMode: record.viewMode ?? DEFAULT_SETTINGS.viewMode,
+          splitRatio: record.splitRatio ?? DEFAULT_SETTINGS.splitRatio,
+          sidebarCollapsed: record.sidebarCollapsed ?? DEFAULT_SETTINGS.sidebarCollapsed,
+          sidebarWidth: record.sidebarWidth ?? DEFAULT_SETTINGS.sidebarWidth
         }
       }
     } catch {
@@ -20,10 +20,9 @@ export const settingsRepository = {
     return { ...DEFAULT_SETTINGS }
   },
 
+  // M-09: 使用 put 直接合并，避免读写竞争
   async save(settings: Partial<Settings>): Promise<void> {
-    const current = await this.load()
-    const merged = { ...current, ...settings }
-    const record: SettingsRecord = { id: 'default', ...merged }
-    await db.settings.put(record)
+    const record: Partial<SettingsRecord> = { id: 'default', ...settings }
+    await db.settings.put(record as SettingsRecord)
   }
 }
diff --git a/src/renderer/hooks/useFileWatch.ts b/src/renderer/hooks/useFileWatch.ts
index 4df9a84..b2445ea 100644
--- a/src/renderer/hooks/useFileWatch.ts
+++ b/src/renderer/hooks/useFileWatch.ts
@@ -48,17 +48,14 @@ export function useSearch() {
     return content.substring(0, m.start) + store.replaceText + content.substring(m.end)
   }
 
+  // B-02: 全部替换（从后向前逐个替换）
   const replaceAll = (content: string): string => {
     if (store.matches.length === 0) return content
-    let result = ''
-    let lastEnd = 0
-    // 从后往前替换
+    let result = content
     for (let i = store.matches.length - 1; i >= 0; i--) {
       const m = store.matches[i]
-      result = content.substring(lastEnd, m.start) + store.replaceText + result
-      lastEnd = m.end
+      result = result.substring(0, m.start) + store.replaceText + result.substring(m.end)
     }
-    result = content.substring(0, store.matches[0].start) + result
     return result
   }
 
diff --git a/src/renderer/hooks/useKeyboard.ts b/src/renderer/hooks/useKeyboard.ts
index 4dfef16..34c3e92 100644
--- a/src/renderer/hooks/useKeyboard.ts
+++ b/src/renderer/hooks/useKeyboard.ts
@@ -5,117 +5,58 @@ import { useSearchStore } from '../stores/searchStore'
 import type { ViewMode } from '../types/settings'
 
 export function useKeyboard(handleOpenFile: () => void, handleSave: () => void, handleSaveAs: () => void) {
-  const createTab = useTabStore(s => s.createTab)
-  const closeTab = useTabStore(s => s.closeTab)
-  const activeTabId = useTabStore(s => s.activeTabId)
-  const tabs = useTabStore(s => s.tabs)
-  const switchToTab = useTabStore(s => s.switchToTab)
-  const mruStack = useTabStore(s => s.mruStack)
   const setViewMode = useEditorStore(s => s.setViewMode)
-  const searchStore = useSearchStore
 
+  // M-08: 使用 getState() 而非依赖 tabs/activeTabId 等频繁变化的值
   const handleKeydown = useCallback((e: KeyboardEvent) => {
     const isCtrl = e.ctrlKey || e.metaKey
 
-    if (isCtrl && e.key === 'o') {
-      e.preventDefault()
-      handleOpenFile()
-      return
-    }
-    if (isCtrl && e.key === 's' && !e.shiftKey) {
-      e.preventDefault()
-      handleSave()
-      return
-    }
-    if (isCtrl && e.shiftKey && e.key === 'S') {
-      e.preventDefault()
-      handleSaveAs()
-      return
-    }
-    if (isCtrl && e.key === '1') {
-      e.preventDefault()
-      setViewMode('split')
-      return
-    }
-    if (isCtrl && e.key === '2') {
-      e.preventDefault()
-      setViewMode('editor')
-      return
-    }
-    if (isCtrl && e.key === '3') {
-      e.preventDefault()
-      setViewMode('preview')
-      return
-    }
-    if (isCtrl && e.key === 't') {
-      e.preventDefault()
-      createTab(null, '')
-      return
-    }
+    if (isCtrl && e.key === 'o') { e.preventDefault(); handleOpenFile(); return }
+    if (isCtrl && e.key === 's' && !e.shiftKey) { e.preventDefault(); handleSave(); return }
+    if (isCtrl && e.shiftKey && e.key === 'S') { e.preventDefault(); handleSaveAs(); return }
+    if (isCtrl && e.key === '1') { e.preventDefault(); setViewMode('split'); return }
+    if (isCtrl && e.key === '2') { e.preventDefault(); setViewMode('editor'); return }
+    if (isCtrl && e.key === '3') { e.preventDefault(); setViewMode('preview'); return }
+
+    // M-08: 通过 getState() 读取最新状态
+    const tabState = useTabStore.getState()
+    if (isCtrl && e.key === 't') { e.preventDefault(); tabState.createTab(null, ''); return }
     if (isCtrl && e.key === 'w') {
       e.preventDefault()
-      if (activeTabId) closeTab(activeTabId)
+      if (tabState.activeTabId) tabState.closeTab(tabState.activeTabId)
       return
     }
+
+    // Ctrl+Tab / Ctrl+Shift+Tab
     if (isCtrl && e.key === 'Tab') {
       e.preventDefault()
+      const { tabs, activeTabId, mruStack } = tabState
       if (tabs.length > 1) {
         if (e.shiftKey) {
           if (mruStack.length > 0) {
             const targetId = mruStack[0]
             if (tabs.find(t => t.id === targetId)) {
-              switchToTab(targetId)
+              tabState.switchToTab(targetId)
             }
           }
         } else {
           const idx = tabs.findIndex(t => t.id === activeTabId)
           const next = (idx + 1) % tabs.length
-          switchToTab(tabs[next].id)
+          tabState.switchToTab(tabs[next].id)
         }
       }
       return
     }
 
     // Search & Replace
-    const state = searchStore.getState()
-    if (isCtrl && e.key === 'f') {
-      e.preventDefault()
-      state.setVisible(true)
-      state.setShowReplace(false)
-      return
-    }
-    if (isCtrl && e.key === 'h') {
-      e.preventDefault()
-      state.setVisible(true)
-      state.setShowReplace(true)
-      return
-    }
-    if (e.key === 'Escape' && state.isVisible) {
-      e.preventDefault()
-      state.close()
-      return
-    }
-    if (e.altKey && e.key === 'c') {
-      e.preventDefault()
-      state.toggleCaseSensitive()
-      return
-    }
-    if (e.altKey && e.key === 'r') {
-      e.preventDefault()
-      state.toggleRegex()
-      return
-    }
-    if (isCtrl && e.shiftKey && e.key === 'G') {
-      e.preventDefault()
-      state.findPrev()
-      return
-    }
-    if (isCtrl && e.shiftKey && e.key === 'H') {
-      e.preventDefault()
-      // replaceAll 需要外部实现
-      return
-    }
-  }, [handleOpenFile, handleSave, handleSaveAs, createTab, closeTab, activeTabId, tabs, switchToTab, mruStack, setViewMode, searchStore])
+    const searchState = useSearchStore.getState()
+    if (isCtrl && e.key === 'f') { e.preventDefault(); searchState.setVisible(true); searchState.setShowReplace(false); return }
+    if (isCtrl && e.key === 'h') { e.preventDefault(); searchState.setVisible(true); searchState.setShowReplace(true); return }
+    if (e.key === 'Escape' && searchState.isVisible) { e.preventDefault(); searchState.close(); return }
+    if (e.altKey && e.key === 'c') { e.preventDefault(); searchState.toggleCaseSensitive(); return }
+    if (e.altKey && e.key === 'r') { e.preventDefault(); searchState.toggleRegex(); return }
+    if (isCtrl && e.shiftKey && e.key === 'G') { e.preventDefault(); searchState.findPrev(); return }
+  }, [handleOpenFile, handleSave, handleSaveAs, setViewMode])
 
   useEffect(() => {
     document.addEventListener('keydown', handleKeydown)
diff --git a/src/renderer/hooks/useSettings.ts b/src/renderer/hooks/useSettings.ts
index d7ba0c2..d9dbbb0 100644
--- a/src/renderer/hooks/useSettings.ts
+++ b/src/renderer/hooks/useSettings.ts
@@ -1,4 +1,4 @@
-import { useEffect } from 'react'
+import { useEffect, useCallback } from 'react'
 import { useEditorStore } from '../stores/editorStore'
 import { settingsRepository } from '../db/settingsRepository'
 import type { ViewMode } from '../types/settings'
@@ -12,20 +12,21 @@ export function useSettings() {
   // 初始化
   useEffect(() => {
     settingsRepository.load().then(settings => {
-      setViewMode(settings.viewMode)
-      setSplitRatio(settings.splitRatio)
+      setViewMode(settings.viewMode ?? 'split')
+      setSplitRatio(settings.splitRatio ?? 50)
     })
   }, [setViewMode, setSplitRatio])
 
-  const saveViewMode = (mode: ViewMode) => {
+  // M-10: 使用 useCallback 稳定函数引用
+  const saveViewMode = useCallback((mode: ViewMode) => {
     setViewMode(mode)
     settingsRepository.save({ viewMode: mode })
-  }
+  }, [setViewMode])
 
-  const saveSplitRatio = (ratio: number) => {
+  const saveSplitRatio = useCallback((ratio: number) => {
     setSplitRatio(ratio)
     settingsRepository.save({ splitRatio: ratio })
-  }
+  }, [setSplitRatio])
 
   return { viewMode, splitRatio, saveViewMode, saveSplitRatio }
 }
diff --git a/src/renderer/hooks/useTheme.ts b/src/renderer/hooks/useTheme.ts
index 60e0aa3..3d698ab 100644
--- a/src/renderer/hooks/useTheme.ts
+++ b/src/renderer/hooks/useTheme.ts
@@ -1,21 +1,24 @@
-import { useEffect } from 'react'
+import { useEffect, useRef } from 'react'
 import { useEditorStore } from '../stores/editorStore'
 import { settingsRepository } from '../db/settingsRepository'
 
 export function useTheme() {
   const darkMode = useEditorStore(s => s.darkMode)
   const setDarkMode = useEditorStore(s => s.setDarkMode)
+  const isInitialized = useRef(false)
 
-  // 初始化：从 IndexedDB 加载主题设置
+  // B-05: 从 IndexedDB 加载主题设置
   useEffect(() => {
     settingsRepository.load().then(settings => {
       const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches
       setDarkMode(settings.darkMode !== undefined ? settings.darkMode : prefersDark)
+      isInitialized.current = true
     })
   }, [setDarkMode])
 
-  // 应用主题到 DOM
+  // B-05: 首次加载完成后才保存主题设置
   useEffect(() => {
+    if (!isInitialized.current) return
     document.documentElement.classList.toggle('dark', darkMode)
     settingsRepository.save({ darkMode })
   }, [darkMode])
diff --git a/src/renderer/lib/fileUtils.ts b/src/renderer/lib/fileUtils.ts
index 6ecc85a..94bced0 100644
--- a/src/renderer/lib/fileUtils.ts
+++ b/src/renderer/lib/fileUtils.ts
@@ -11,10 +11,14 @@ export function getFileName(filePath: string): string {
 }
 
 export function isAllowedFile(filePath: string): boolean {
-  const ext = filePath.substring(filePath.lastIndexOf('.')).toLowerCase()
+  const ext = getFileExtension(filePath)
   return (ALLOWED_EXTENSIONS as readonly string[]).includes(ext)
 }
 
+// L-07: 无扩展名文件正确返回空字符串
 export function getFileExtension(filePath: string): string {
-  return filePath.substring(filePath.lastIndexOf('.')).toLowerCase()
+  const name = filePath.split(/[/\\]/).pop() || filePath
+  const dotIndex = name.lastIndexOf('.')
+  if (dotIndex <= 0) return '' // 无扩展名或以 . 开头的隐藏文件
+  return name.substring(dotIndex).toLowerCase()
 }
diff --git a/src/renderer/lib/scrollSync.ts b/src/renderer/lib/scrollSync.ts
index 75bfca5..673e864 100644
--- a/src/renderer/lib/scrollSync.ts
+++ b/src/renderer/lib/scrollSync.ts
@@ -1,10 +1,12 @@
 // 滚动同步算法 — 基于块级元素 DOM 位置映射
-import type { SearchMatch } from '../types/search'
 
 export interface ScrollMap {
   lineToPreviewMap: Float32Array
 }
 
+// B-06: 用 NaN 标记未映射状态（0 是合法的 offsetTop）
+const UNMAPPED = NaN
+
 // 识别块级元素起始行
 function identifyBlockStarts(lines: string[]): Set<number> {
   const starts = new Set<number>()
@@ -13,8 +15,8 @@ function identifyBlockStarts(lines: string[]): Set<number> {
   for (let i = 0; i < lines.length; i++) {
     const line = lines[i].trimStart()
 
-    // 围栏代码块边界
-    if (line.startsWith('```')) {
+    // 围栏代码块边界（仅匹配 ``` 开头，不匹配 `````` 等）
+    if (/^`{3,}(?!`)/.test(line)) {
       if (!inCodeBlock) starts.add(i)
       inCodeBlock = !inCodeBlock
       continue
@@ -48,7 +50,7 @@ export function buildScrollMap(
 ): ScrollMap {
   const lines = markdown.split('\n')
   const totalLines = lines.length
-  const lineToPreviewMap = new Float32Array(totalLines)
+  const lineToPreviewMap = new Float32Array(totalLines).fill(UNMAPPED)
 
   // 1. 识别块级元素起始行
   const blockStarts = identifyBlockStarts(lines)
@@ -81,16 +83,16 @@ export function buildScrollMap(
 
   // 4. 线性插值填充所有行
   for (let i = 0; i < totalLines; i++) {
-    if (lineToPreviewMap[i] !== 0 && uniqueStartsSet.has(i)) continue
+    if (!isNaN(lineToPreviewMap[i]) && uniqueStartsSet.has(i)) continue
 
     // 找到前后最近的已映射行
     let prevLine = -1
     let nextLine = -1
     for (let j = i - 1; j >= 0; j--) {
-      if (lineToPreviewMap[j] !== 0 || uniqueStartsSet.has(j)) { prevLine = j; break }
+      if (!isNaN(lineToPreviewMap[j]) || 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 (!isNaN(lineToPreviewMap[j]) || uniqueStartsSet.has(j)) { nextLine = j; break }
     }
 
     if (prevLine === -1 && nextLine === -1) {
diff --git a/src/renderer/stores/tabStore.ts b/src/renderer/stores/tabStore.ts
index 93f6fbe..473eb84 100644
--- a/src/renderer/stores/tabStore.ts
+++ b/src/renderer/stores/tabStore.ts
@@ -1,4 +1,5 @@
 import { create } from 'zustand'
+import { nanoid } from 'nanoid'
 import type { Tab } from '../types/tab'
 
 interface TabState {
@@ -16,8 +17,7 @@ interface TabState {
   updateTabScroll: (tabId: string, scroll: Partial<Pick<Tab, 'scrollTop' | 'scrollLeft' | 'selectionStart' | 'selectionEnd' | 'previewScrollTop'>>) => void
 }
 
-let tabIdCounter = 0
-
+// L-04: 使用 nanoid 替代计数器（HMR 安全）
 export const useTabStore = create<TabState>((set, get) => ({
   tabs: [],
   activeTabId: null,
@@ -34,7 +34,7 @@ export const useTabStore = create<TabState>((set, get) => ({
     }
 
     const tab: Tab = {
-      id: String(++tabIdCounter),
+      id: nanoid(),
       filePath,
       content,
       isModified: false,
diff --git a/src/renderer/styles/global.css b/src/renderer/styles/global.css
index ca776d8..56dca68 100644
--- a/src/renderer/styles/global.css
+++ b/src/renderer/styles/global.css
@@ -752,6 +752,9 @@ html, body {
 #app.mode-preview #editor-panel,
 #app.mode-preview #resizer { display: none; }
 
+#app.mode-editor #preview-panel,
+#app.mode-editor #resizer { display: none; }
+
 /* Toast */
 #toast-notification {
   position: fixed;