perf(sidebar): fs.tree 22.8ms→3.8ms + 删除工作区路径检测（放开权限）+ 树展开状态按会话

用户实测反馈：

1) `/sidebar/api/fs.tree` 性能极差 —— 先测后改（10k 条目目录、热缓存、中位数）：
   - 冷调用 cap=1000：22.76ms → **3.77ms**；TTL 内重复：≈23ms → **0.000ms**
   - 改法：opendir for-await → readdir(withFileTypes) 一次取回；只为 cap 条建行
     （slice + 定长数组）；路径用字符串拼接而非 path.join；排序弃 localeCompare
     （14.6ms/10k → 0.35ms）改小写比较 + 原名码点兜底；新增 1.5s 目录级缓存
     （键 绝对路径\0cap，上限 512），由 fs.write/rename/remove/mkdir/upload 与
     fs-watch 的变更通知显式失效
   - 契约逐字不变；新增 tests/fs-tree.spec.ts 6 例 + fs-watch 失效用例（判别性验证）

2) 删除工作区路径检测（默认不检测、放开权限）：
   - path-security 变纯词法解析（realpath/包含性判定删除）、fs-operations 去 fence
     分支、所有 fs 路由不再读 fence、403 分支消失、config 删 workspaceFence 字段
     （schemastery 容忍未知键，旧 profile 不会加载失败）、settings 开关删除
   - ⚠️ 安全影响：插件 fs 路由（tree/read/write/rename/remove/mkdir/媒体/HTML/
     upload/archive）现在可读写宿主用户可访问的任意路径，只受 OS 权限约束；
     指南 §8.1 已加醒目声明
   - 死代码清理：FenceErrorNotice 组件 + EditorHost 分支 + 4 个词条（settingsFence*、
     fenceErrorReason、fenceDisableAction）+ isOutsideWorkspace* 助手 + TreePanel 的
     store prop + 相关 CSS 块

3) 批量列举路由 `fs.trees`（单层失败只在该层带 error）+ 客户端批量加载：
   挂载/刷新时的 N+1 请求变为 1 个（8 个展开目录：9 → 1，探针断言）
   refreshTick 不再先清缓存（旧行保留到新答案；失败保留旧行 + warn 提示）

4) 修复「关闭文件后返回文件树，展开状态被重置」：
   原生承载面的展开集合原来存在每个 tab 的记录里（drop 即丢），改为**每会话状态**
   的投影（ensure 从会话态读、toggleExpanded 写回会话态、registerNativeSurface 用
   attachStore 订阅）；同一会话多 tab 共享、不同会话隔离；revealed 保持 per-tab

验证：typecheck / lint / test（136 文件 / 1484 通过 / 9 跳过）/ build 全绿；
DSH_CMD='npx -y --package @deepseek-ai/dsh@0.1.7-rc.1 dsh' pnpm test:mount 7/7 通过；
版本镜像同步（dsh.plugin.json + SIDEBAR_SERVICE_VERSION）

tests/native-surface.spec.ts

@@ -11,7 +11,7 @@ import { act } from 'react-dom/test-utils'
 import { createNativeTabRecords, NativeTabBody, NativeTabTitle } from '../src/client/native/tab-adapter.tsx'
 import { registerNativeSurface } from '../src/client/native/index.ts'
 import { createBetterSidebarService, type SidebarSurface } from '../src/client/service.ts'
-import { createSidebarStore, type SidebarTab } from '../src/client/state.ts'
+import { createSidebarStore, toggleExpanded, type SidebarTab } from '../src/client/state.ts'
 
 const scope = { sessionId: 's1', cwd: '/work' }
 
@@ -45,17 +45,89 @@ describe('createNativeTabRecords', () => {
     expect(view.tab).toMatchObject({ id: 'tab-3', path: '/work/b.ts', title: 'renamed.ts' })
   })
 
-  it('tracks expansion per record and bumps its version', () => {
+  it('tracks expansion in the SESSION state and bumps the record version', () => {
+    const store = createSidebarStore()
+    store.setSession('s1')
     const records = createNativeTabRecords()
+    records.attachStore(store)
     records.ensure({ id: 'tab-4', kind: 'editor', title: 'Files', params: undefined, scope })
     const before = records.versionOf('tab-4')
     records.toggleExpanded('tab-4', '/work/src')
     expect(records.get('tab-4')?.expanded).toEqual(['/work/src'])
+    expect(store.getSessionStates().get('s1')?.expanded).toEqual(['/work/src'])
     expect(records.versionOf('tab-4')).toBeGreaterThan(before)
     records.toggleExpanded('tab-4', '/work/src')
     expect(records.get('tab-4')?.expanded).toEqual([])
   })
 
+  it('keeps the expansion after a tab record is DROPPED and rebuilt (the reported bug)', () => {
+    // The user's flow: open a file preview (the files tab unmounts and its
+    // native record is dropped), close it, return to the files page — a NEW
+    // record for the SAME session must show the set the user had.
+    const store = createSidebarStore()
+    store.setSession('s1')
+    const records = createNativeTabRecords()
+    records.attachStore(store)
+    records.ensure({ id: 'files-1', kind: 'files', title: 'Files', params: undefined, scope })
+    records.toggleExpanded('files-1', '/work/src')
+    records.toggleExpanded('files-1', '/work/src/components')
+    expect(records.get('files-1')?.expanded).toEqual(['/work/src', '/work/src/components'])
+
+    records.drop('files-1')
+    const rebuilt = records.ensure({ id: 'files-2', kind: 'files', title: 'Files', params: undefined, scope })
+    expect(rebuilt.expanded).toEqual(['/work/src', '/work/src/components'])
+  })
+
+  it('shares one expansion set between two native tabs of the same session', () => {
+    const store = createSidebarStore()
+    store.setSession('s1')
+    const records = createNativeTabRecords()
+    records.attachStore(store)
+    records.ensure({ id: 'files-a', kind: 'files', title: 'Files', params: undefined, scope })
+    records.ensure({ id: 'files-b', kind: 'files', title: 'Files', params: undefined, scope })
+
+    records.toggleExpanded('files-a', '/work/src')
+    expect(records.get('files-b')?.expanded).toEqual(['/work/src'])
+
+    // The WORKBENCH's own toggle (the per-session reducer) is the same state.
+    store.reduce(state => toggleExpanded(state, '/work/lib'))
+    expect(records.get('files-a')?.expanded).toEqual(['/work/src', '/work/lib'])
+    expect(records.get('files-b')?.expanded).toEqual(['/work/src', '/work/lib'])
+
+    // …and a toggle from the native side is visible to the workbench reducer's
+    // state (one authority, two surfaces).
+    records.toggleExpanded('files-b', '/work/src')
+    expect(store.getSessionStates().get('s1')?.expanded).toEqual(['/work/lib'])
+  })
+
+  it('keeps two sessions apart (a native tab in each)', () => {
+    const store = createSidebarStore()
+    store.setSession('s1')
+    const records = createNativeTabRecords()
+    records.attachStore(store)
+    records.ensure({ id: 's1-files', kind: 'files', title: 'Files', params: undefined, scope })
+    records.ensure({ id: 's2-files', kind: 'files', title: 'Files', params: undefined, scope: { sessionId: 's2', cwd: '/other' } })
+
+    // The ACTIVE session goes through `reduce`; the background one through
+    // `reduceFor` — both must land in their own session only.
+    records.toggleExpanded('s1-files', '/work/src')
+    records.toggleExpanded('s2-files', '/other/lib')
+    expect(records.get('s1-files')?.expanded).toEqual(['/work/src'])
+    expect(records.get('s2-files')?.expanded).toEqual(['/other/lib'])
+    expect(store.getSessionStates().get('s1')?.expanded).toEqual(['/work/src'])
+    expect(store.getSessionStates().get('s2')?.expanded).toEqual(['/other/lib'])
+  })
+
+  it('reflects a store change made while no view is subscribed yet', () => {
+    const store = createSidebarStore()
+    store.setSession('s1')
+    store.reduce(state => toggleExpanded(state, '/work/src'))
+    const records = createNativeTabRecords()
+    records.attachStore(store)
+    const view = records.ensure({ id: 'late', kind: 'files', title: 'Files', params: undefined, scope })
+    expect(view.expanded).toEqual(['/work/src'])
+  })
+
   it('notifies subscribers and forgets a dropped record', () => {
     const records = createNativeTabRecords()
     records.ensure({ id: 'tab-5', kind: 'terminal', title: 'Terminal', params: undefined, scope })