diff --git a/src/main/file-system.ts b/src/main/file-system.ts
index 9148729..caf5c80 100644
--- a/src/main/file-system.ts
+++ b/src/main/file-system.ts
@@ -1,6 +1,5 @@
-import { readFile, stat, writeFile, readdir, rename } from 'fs/promises'
-import { join, extname, basename } from 'path'
-import { tmpdir } from 'os'
+import { readFile, stat, writeFile, rename, readdir, unlink } from 'fs/promises'
+import { join, extname, dirname, basename } from 'path'
 import type { ReadFileResult, SaveFileResult, FileNode } from '../shared/types'
 
 const MAX_FILE_SIZE = 20 * 1024 * 1024 // 20MB
@@ -10,7 +9,6 @@ const SKIP_DIRS = new Set([
   '.next', '.nuxt', '__pycache__', '.DS_Store'
 ])
 
-// L-09: 使用 shared 类型
 export async function readFileContent(filePath: string): Promise<ReadFileResult> {
   try {
     const fileStat = await stat(filePath)
@@ -18,7 +16,6 @@ export async function readFileContent(filePath: string): Promise<ReadFileResult>
       return { success: false, error: `文件过大（${(fileStat.size / 1024 / 1024).toFixed(1)} MB），暂不支持超过 20MB 的文件` }
     }
     let content = await readFile(filePath, 'utf-8')
-    // 剥离 UTF-8 BOM
     if (content.charCodeAt(0) === 0xFEFF) content = content.slice(1)
     return { success: true, content }
   } catch (err) {
@@ -26,20 +23,21 @@ export async function readFileContent(filePath: string): Promise<ReadFileResult>
   }
 }
 
-// M-06: 原子写入（write-to-temp-then-rename）
+// C-02: 临时文件写到与目标相同目录（避免跨盘 rename 失败）
 export async function saveFileContent(filePath: string, content: string): Promise<SaveFileResult> {
+  const tmpFile = join(dirname(filePath), `.marklite-tmp-${Date.now()}-${basename(filePath)}`)
   try {
-    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) {
+    // 清理残留临时文件
+    try { await unlink(tmpFile) } catch { /* ignore */ }
     return { success: false, error: (err as Error).message }
   }
 }
 
-// M-05: 添加递归深度限制 + 每个 entry 错误边界
+// M-05: 递归深度限制 + 错误边界
 export async function buildDirTree(dirPath: string, depth = 0, maxDepth = 10): Promise<FileNode[]> {
   if (depth > maxDepth) return []
 
@@ -47,7 +45,7 @@ export async function buildDirTree(dirPath: string, depth = 0, maxDepth = 10): P
   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
+    return []
   }
 
   entries.sort((a, b) => {
diff --git a/src/main/file-watcher.ts b/src/main/file-watcher.ts
index 1c752b1..392d843 100644
--- a/src/main/file-watcher.ts
+++ b/src/main/file-watcher.ts
@@ -22,10 +22,13 @@ export class FileWatcher {
           }
         }
       })
-      // M-04: 监听 error 事件，文件被删除时清理状态
+      // L-02: 监听 error 事件，文件被删除时显式关闭并清理状态
       this.watcher.on('error', () => {
+        if (this.watcher) {
+          this.watcher.close()
+          this.watcher = null
+        }
         this.currentPath = null
-        this.watcher = null
       })
     } catch {
       // silently ignore
@@ -74,9 +77,12 @@ export class SidebarWatcher {
           }, 300)
         }
       })
-      // M-04: 监听 error 事件
+      // L-02: 监听 error 事件，显式关闭
       this.watcher.on('error', () => {
-        this.watcher = null
+        if (this.watcher) {
+          this.watcher.close()
+          this.watcher = null
+        }
         this.watchPath = null
       })
     } catch {
diff --git a/src/main/index.ts b/src/main/index.ts
index fa8f9ba..ec94e21 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -30,7 +30,6 @@ function openFileInTab(filePath: string): void {
   })
 }
 
-// 单实例锁
 const lockOk = setupSingleInstanceLock((filePath) => {
   if (mainWindow && !mainWindow.isDestroyed()) {
     if (mainWindow.isMinimized()) mainWindow.restore()
@@ -72,11 +71,15 @@ if (!lockOk) {
     })
   }
 
-  // B-07: 完整的窗口初始化逻辑（activate 复用）
+  // C-05: 窗口重建时重置状态
   function initWindow(): void {
-    mainWindow = createWindow()
+    state.isClosing = false
+    if (state.closeTimeout) {
+      clearTimeout(state.closeTimeout)
+      state.closeTimeout = null
+    }
 
-    registerIpcHandlers(() => mainWindow, fileWatcher, sidebarWatcher, state)
+    mainWindow = createWindow()
 
     if (process.env.ELECTRON_RENDERER_URL) {
       mainWindow.loadURL(process.env.ELECTRON_RENDERER_URL)
@@ -112,9 +115,11 @@ if (!lockOk) {
       }
     })
 
+    // C-03: IPC 处理器只注册一次
+    registerIpcHandlers(() => mainWindow, fileWatcher, sidebarWatcher, state)
+
     initWindow()
 
-    // 命令行文件
     const cmdFile = getFilePathFromArgs(process.argv)
     if (cmdFile) {
       state.pendingFilePath = cmdFile
@@ -125,7 +130,7 @@ if (!lockOk) {
     if (process.platform !== 'darwin') app.quit()
   })
 
-  // B-07: macOS activate 完整重建窗口
+  // C-03: activate 只重建窗口，不重复注册 IPC
   app.on('activate', () => {
     if (BrowserWindow.getAllWindows().length === 0) {
       initWindow()
diff --git a/src/renderer/components/Sidebar/Sidebar.tsx b/src/renderer/components/Sidebar/Sidebar.tsx
index fae158c..57e3b3d 100644
--- a/src/renderer/components/Sidebar/Sidebar.tsx
+++ b/src/renderer/components/Sidebar/Sidebar.tsx
@@ -19,18 +19,25 @@ export function Sidebar() {
   const isVisible = useSidebarStore(s => s.isVisible)
   const expandDirs = useSidebarStore(s => s.expandDirs)
 
-  // 计算当前活动标签的文件路径（用于文件树高亮）
+  // M-01: 归一化路径分隔符（Windows 混合 \\ 和 /）
+  const norm = (p: string) => p.replace(/\\/g, '/')
   const activeFilePath = tabs.find(t => t.id === activeTabId)?.filePath ?? null
 
   // 自动展开到活动文件所在的目录
   useEffect(() => {
     if (!activeFilePath || !rootPath) return
-    if (!activeFilePath.startsWith(rootPath)) return
+    // M-01: 归一化后比较
+    const normActive = norm(activeFilePath)
+    const normRoot = norm(rootPath)
+    if (!normActive.startsWith(normRoot)) return
 
     // 提取文件的所有父目录路径
     const dirsToExpand: string[] = []
     let dir = activeFilePath.replace(/[/\\][^/\\]+$/, '') // 移除文件名
-    while (dir && dir.length >= rootPath.length && dir !== rootPath) {
+    // M-02: 添加 prev 防护无限循环
+    let prev = ''
+    while (dir && dir.length >= rootPath.length && dir !== rootPath && dir !== prev) {
+      prev = dir
       dirsToExpand.push(dir)
       dir = dir.replace(/[/\\][^/\\]+$/, '')
     }
@@ -107,10 +114,11 @@ export function Sidebar() {
       }
     }
   }, [tabs, switchToTab, createTab])
+  // M-01: 独立文件区（归一化路径比较）
   const independentFiles = tabs.filter(t => {
     if (!t.filePath) return false
     if (!rootPath) return true
-    return !t.filePath.startsWith(rootPath)
+    return !norm(t.filePath).startsWith(norm(rootPath))
   })
 
   if (!isVisible) return null
diff --git a/src/renderer/components/TabBar/TabBar.tsx b/src/renderer/components/TabBar/TabBar.tsx
index 75b3765..4bf2375 100644
--- a/src/renderer/components/TabBar/TabBar.tsx
+++ b/src/renderer/components/TabBar/TabBar.tsx
@@ -33,11 +33,15 @@ export function TabBar() {
     closeTab(tabId)
   }, [tabs, closeTab])
 
-  // 右键菜单
+  // C-06: 右键菜单（带边界修正）
   const handleContextMenu = useCallback((e: React.MouseEvent, tabId: string) => {
     e.preventDefault()
     e.stopPropagation()
-    setMenu({ visible: true, x: e.clientX, y: e.clientY, tabId })
+    const MENU_WIDTH = 170
+    const MENU_HEIGHT = 140
+    const x = Math.min(e.clientX, window.innerWidth - MENU_WIDTH)
+    const y = Math.min(e.clientY, window.innerHeight - MENU_HEIGHT)
+    setMenu({ visible: true, x: Math.max(0, x), y: Math.max(0, y), tabId })
   }, [])
 
   // 点击空白处关闭菜单
@@ -147,9 +151,12 @@ export function TabBar() {
           <div className="tab-context-item" onClick={handleMenuClose}>
             关闭
           </div>
-          <div className="tab-context-item" onClick={handleMenuCloseOthers}>
-            关闭其他标签
-          </div>
+          {/* M-03: 单标签时隐藏"关闭其他标签" */}
+          {tabs.length > 1 && (
+            <div className="tab-context-item" onClick={handleMenuCloseOthers}>
+              关闭其他标签
+            </div>
+          )}
           {hasRightTabs && (
             <div className="tab-context-item" onClick={handleMenuCloseRight}>
               关闭右侧标签
diff --git a/src/renderer/db/settingsRepository.ts b/src/renderer/db/settingsRepository.ts
index 51dbcea..c135e7c 100644
--- a/src/renderer/db/settingsRepository.ts
+++ b/src/renderer/db/settingsRepository.ts
@@ -20,9 +20,10 @@ 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 record: Partial<SettingsRecord> = { id: 'default', ...settings }
-    await db.settings.put(record as SettingsRecord)
+  // C-01: 先 load 再 merge 再 put，避免部分字段丢失
+  async save(partial: Partial<Settings>): Promise<void> {
+    const current = await this.load()
+    const merged: SettingsRecord = { id: 'default', ...current, ...partial }
+    await db.settings.put(merged)
   }
 }
diff --git a/src/renderer/hooks/useFileWatch.ts b/src/renderer/hooks/useFileWatch.ts
index b2445ea..093ea66 100644
--- a/src/renderer/hooks/useFileWatch.ts
+++ b/src/renderer/hooks/useFileWatch.ts
@@ -1,9 +1,5 @@
 import { useEffect } from 'react'
 import { useTabStore } from '../stores/tabStore'
-import { useSearchStore } from '../stores/searchStore'
-import { useEditorStore } from '../stores/editorStore'
-import { findMatches } from '../lib/searchEngine'
-import type { SearchMatch } from '../types/search'
 
 export function useFileWatch() {
   const getActiveTab = useTabStore(s => s.getActiveTab)
@@ -14,7 +10,6 @@ export function useFileWatch() {
     window.electronAPI.onExternalModification((filePath: string) => {
       const tab = getActiveTab()
       if (tab && tab.filePath === filePath) {
-        // 显示修改横幅（通过状态管理触发 UI 更新）
         window.dispatchEvent(new CustomEvent('file-externally-modified', { detail: filePath }))
       }
     })
@@ -24,40 +19,3 @@ export function useFileWatch() {
     }
   }, [getActiveTab])
 }
-
-// 搜索 Hook
-export function useSearch() {
-  const store = useSearchStore()
-
-  const doSearch = (content: string) => {
-    if (!store.searchText) {
-      store.setMatches([])
-      return
-    }
-    const matches = findMatches(content, store.searchText, store.options)
-    store.setMatches(matches)
-    if (matches.length > 0) {
-      // 找到离光标最近的匹配
-      store.setCurrentIndex(0)
-    }
-  }
-
-  const replaceCurrent = (content: string): string | null => {
-    if (store.matches.length === 0 || store.currentIndex < 0) return null
-    const m = store.matches[store.currentIndex]
-    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 = content
-    for (let i = store.matches.length - 1; i >= 0; i--) {
-      const m = store.matches[i]
-      result = result.substring(0, m.start) + store.replaceText + result.substring(m.end)
-    }
-    return result
-  }
-
-  return { ...store, doSearch, replaceCurrent, replaceAll }
-}
diff --git a/src/renderer/lib/markdown.ts b/src/renderer/lib/markdown.ts
index f80ec09..924f2ec 100644
--- a/src/renderer/lib/markdown.ts
+++ b/src/renderer/lib/markdown.ts
@@ -23,6 +23,8 @@ function rehypeFixImages(filePath: string | null): Plugin<[], Root> {
         if (child.type === 'element' && child.tagName === 'img') {
           const src = child.properties?.src as string | undefined
           if (src && !src.startsWith('http://') && !src.startsWith('https://') && !src.startsWith('data:') && !src.startsWith('file://')) {
+            // C-04: 拒绝路径遍历攻击
+            if (src.includes('..')) return
             // 相对路径转绝对路径
             child.properties = {
               ...child.properties,
diff --git a/src/renderer/stores/tabStore.ts b/src/renderer/stores/tabStore.ts
index 8db67d3..799ed39 100644
--- a/src/renderer/stores/tabStore.ts
+++ b/src/renderer/stores/tabStore.ts
@@ -69,8 +69,15 @@ export const useTabStore = create<TabState>((set, get) => ({
         if (newTabs.length === 0) {
           newActiveId = null
         } else {
-          const newIndex = Math.min(index, newTabs.length - 1)
-          newActiveId = newTabs[newIndex].id
+          // M-05: 优先从 MRU 栈取最近使用的标签
+          const mruCandidate = newMru.find(id => newTabs.some(t => t.id === id))
+          if (mruCandidate) {
+            newActiveId = mruCandidate
+            newMru.splice(newMru.indexOf(mruCandidate), 1)
+          } else {
+            const newIndex = Math.min(index, newTabs.length - 1)
+            newActiveId = newTabs[newIndex].id
+          }
         }
       }
 
diff --git a/src/renderer/styles/global.css b/src/renderer/styles/global.css
index e100eba..9a72ac1 100644
--- a/src/renderer/styles/global.css
+++ b/src/renderer/styles/global.css
@@ -269,7 +269,8 @@ html, body {
 }
 
 .tab-item:hover .tab-close,
-.tab-item.active .tab-close { opacity: 1; }
+.tab-item.active .tab-close,
+.tab-item.modified .tab-close { opacity: 1; }
 
 .tab-close:hover {
   background: var(--border);
@@ -371,6 +372,11 @@ html, body {
   color: #000;
 }
 
+:root.dark .banner-btn:hover {
+  background: #665500;
+  color: #ffd54f;
+}
+
 /* Status Bar */
 #statusbar {
   height: var(--statusbar-height);