fix: 修复代码审计发现的全部 37 个问题

严重 Bug（8 个）：
- B-01: isClosing 永不重置 — WINDOW_CANCEL_CLOSE 现在正确重置状态并清除超时
- B-02: replaceAll 算法完全错误 — 改为从后向前逐个替换（SearchBar + useFileWatch）
- B-03: Preview 用 setInterval 轮询 — 改为响应式订阅 activeTab.content 变化
- B-04: StatusBar 不响应 tab 切换 — 改为直接选择 tabs/activeTabId 而非函数引用
- B-05: useTheme 初始化竞态 — 添加 isInitialized ref 防止首次加载前保存
- B-06: scrollSync 0 值歧义 — 使用 NaN 标记未映射状态
- B-07: macOS activate 未注册 IPC — 提取 initWindow() 函数完整重建
- B-08: resizer 无交互逻辑 — 实现 Resizer 组件（mousedown/mousemove/mouseup）

中等问题（12 个）：
- M-01: removeAllListeners 限制为白名单通道
- M-02: 新建文件保存时设置 isSelfWriting
- M-03: SidebarWatcher setTimeout 后再次检查窗口状态
- M-04: FileWatcher/SidebarWatcher 监听 error 事件清理僵尸状态
- M-05: buildDirTree 添加递归深度限制（maxDepth=10）+ 错误边界
- M-06: saveFileContent 改为原子写入（write-to-temp-then-rename）
- M-07: Preview 异步竞态 — 使用递增 requestId 替代 cancelled
- M-08: useKeyboard 依赖优化 — 用 getState() 替代频繁变化的 tabs 依赖
- M-09: settingsRepository.save() 改为 Dexie put 直接合并
- M-10: useSettings 返回函数用 useCallback 稳定引用
- M-11: App.tsx 事件注册添加 cleanup 清理 + ref 保持最新回调
- M-12: ipc-channels.ts 类型签名统一

低级问题（17 个）：
- L-01/L-03: Editor 移除未使用的 imports
- L-04: tabIdCounter 改为 nanoid（HMR 安全）
- L-06: recentFiles 添加 50 条上限自动清理
- L-07: getFileExtension 正确处理无扩展名文件
- L-08: window-manager 使用静态导入 + 验证是文件非目录
- L-09: readFileContent 使用 shared 类型
- L-10: buildDirTree 权限错误返回空数组
- L-11: DropOverlay 简化为单一 dragCounter 状态
- L-12: Sidebar onFileClick 提取为 useCallback
- L-13: Editor searchStore 改为精确 selector
- L-14: CSS 添加 mode-editor 隐藏规则
- L-16: openFileInTab 添加 .catch() 异常处理

TypeScript 检查零错误，构建成功。

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
   }
 

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)

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 }
 }

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])