refactor(i18n): 覆盖只在 DSH active=en 时生效（借用英文槽位）

better-locale 的覆盖本质上是借用 DSH 的英文槽位来渲染第三语言：
- store.getOverride(dshActive, ns, key) 改为只在 dshActive === 'en'
  时返回覆盖文本；DSH 在 zh 下覆盖完全惰性（保持原生 zh）
- 新增 store.isOverrideActive(dshActive)：返回 active !== undefined
  && dshActive === 'en'，供 better-sidebar 的 isZh() 判断
- isZh() 改用 isOverrideActive(dshActive) 判断（仅在 DSH=en 且有
  override 时返回 false），zh 下返回 true
- LanguageSwitcher 接收 dshActive prop，选了非 native 且 DSH 非 en
  时显示「请将 DSH 切换到英文以查看 [语言名]」提示
- 新增 switchToEnHint copy key（zh + en）
- 测试：better-locale +3 store tests（en-only / inert on zh /
  isOverrideActive），+1 patch test（inert on zh）；better-sidebar
  +1 locales test（override inert while DSH on zh），FakeBetterLocale
  加 isOverrideActive 方法

AGENTS.md

@@ -595,7 +595,7 @@ interface OpenTabSeed {
 | **id 冲突** | `registerTab` / `registerFileViewer` 对重复 id 抛错；建议用包前缀（`my-plugin:xxx`） |
 | **家族右面板互斥（v0.13.0+）** | 读取 `aionui-panel` 设置命名空间的 `rightPanel`：解析为 `'aionui-panel'` 时整个侧边栏不挂载（`settings.get` 路由返回 `externalDisable: true`，客户端挂载门 + 各类接管一并停用；`settings/document-updated` 推送实时生效，无 `remote` 服务的部署回退为启动时判定）。未安装 aionui 或提供方为其他值时不受影响 |
 | **i18n 跟随** | 侧边栏界面文案跟随 DSH 的 `ctx.locale`（`@deepseek-ai/dsh-client-locale`）：词典注册在 `betterSidebar` 命名空间，语言偏好（Host-backed `locale.preference`）与浏览器语言不一致时以 DSH 为准并实时切换；locale 服务缺失时回退浏览器语言。插件自身的 `t()`（`src/client/locales.ts`）由 `apply()` 挂接服务；消费插件**不要**依赖此内部函数——标题等字段传字符串或 `() => string` 即可（i18n 友好）。⚠️ 渲染 DSH 的 `MarkdownText` 时必须传 `codeLabels={{ copyLabel: t('copy'), copiedLabel: t('copied') }}`——该组件 cordis-free，漏传则代码块复制按钮回退硬编码中文 |
-| **第三语言覆盖（ja 等）** | 可选 peer `@huanlin/dsh-plugin-better-locale`（`peerDependenciesMeta.optional: true`）提供 ja/ko/... 等第三语言覆盖。安装后 `apply()` 调 `ctx.get('betterLocale')` 取得 override store 并经 `attachBetterLocale()` 注入 `t()`：`t()` 先查 `store.getOverride(active, 'betterSidebar', key)`，命中则返回覆盖文本（如 ja），否则走原 zh/en 链。Sidebar root 另订阅 store 的 `subscribe()`（uSES on `store.active`），覆盖切换时全树重渲染（DSH locale 的 `active` 字段不变，所以既有 `localeRevision` uSES 不会触发）。本插件同时把 ja 词典 `register('betterSidebar', { ja })` 进 better-locale 的 store，让外部 `ctx.locale.lookup('betterSidebar', key)` 调用者也能拿到 ja 文本。未安装 better-locale 时 `ctx.get` 返回 undefined，整段为 no-op，zh/en 行为不变。新增 zh key 时**必须**同步加 ja 翻译（`src/client/locales-ja.ts`），否则该 key 在 ja 覆盖下回退到 en |
+| **第三语言覆盖（ja 等）** | 可选 peer `@huanlin/dsh-plugin-better-locale`（`peerDependenciesMeta.optional: true`）提供 ja/ko/... 等第三语言覆盖。覆盖**借用 DSH 的英文槽位**：`store.getOverride(dshActive, ns, key)` 只在 `dshActive === 'en'` 时返回覆盖文本，DSH 在 zh 下覆盖完全惰性（保持原生 zh）。安装后 `apply()` 调 `ctx.get('betterLocale')` 取得 override store 并经 `attachBetterLocale()` 注入 `t()`：`t()` 先查 `store.getOverride(active, 'betterSidebar', key)`，命中则返回覆盖文本（如 ja），否则走原 zh/en 链；`isZh()` 改用 `store.isOverrideActive(active)` 判断（仅在 DSH=en 且有 override 时返回 false）。Sidebar root 另订阅 store 的 `subscribe()`（uSES on `store.active`），覆盖切换时全树重渲染（DSH locale 的 `active` 字段不变，所以既有 `localeRevision` uSES 不会触发）。本插件同时把 ja 词典 `register('betterSidebar', { ja })` 进 better-locale 的 store，让外部 `ctx.locale.lookup('betterSidebar', key)` 调用者也能拿到 ja 文本。better-locale 的 LanguageSwitcher 在用户选了非 native 且 DSH 非 en 时显示「请将 DSH 切换到英文以查看 [语言名]」提示。未安装 better-locale 时 `ctx.get` 返回 undefined，整段为 no-op，zh/en 行为不变。新增 zh key 时**必须**同步加 ja 翻译（`src/client/locales-ja.ts`），否则该 key 在 ja 覆盖下回退到 en |
 | **懒加载 chunk** | 内置重依赖（xterm/CodeMirror）在独立 bundle（`lib/client-<name>.js`）中，经 `/sidebar/bundle` 路由按需下发；每个脚本把 factory 赋到插件自有全局注册表 `globalThis.__dshChunks__[<name>]`，由 `src/client/chunk-loader.ts` 用自定义 require（externals 经 `__DSH_MODULES__` seed 分支解析）物化——**不经过** `__ModuleLoader__` 注册；**核心 bundle 禁止静态 import `src/client/chunks/*`**（会把库拖回启动路径）；对消费插件透明——懒加载只作用于内置 descriptor，`component` 契约（`(props) => ReactNode` 纯渲染函数）不变 |
 
 ---

src/client/index.tsx

@@ -73,6 +73,7 @@ export function apply(ctx: Context): void {
     | {
         readonly active: string | undefined
         getOverride(dshActive: string, ns: string, key: string): string | undefined
+        isOverrideActive(dshActive: string): boolean
         register(ns: string, dicts: Record<string, Record<string, string>>): () => void
         subscribe(listener: () => void): () => void
       }

src/client/locales.ts

@@ -703,10 +703,17 @@ let localeService: { getSnapshot(): { active: string } } | undefined
  * (absent → no override; the zh/en chain runs). The store's `active`
  * field holds the user's chosen override id (e.g. `'ja'`); `undefined`
  * means "no override, use DSH native zh/en".
+ *
+ * The override only takes effect when DSH's active locale is `'en'`
+ * (it borrows DSH's English slot to render a third language). While
+ * DSH is on `'zh'` the override is inert — `getOverride` returns
+ * `undefined` and `isOverrideActive` returns `false` — so `t()` and
+ * `isZh()` fall through to the native zh/en chain unchanged.
  */
 let betterLocaleStore: {
   readonly active: string | undefined
   getOverride(dshActive: string, ns: string, key: string): string | undefined
+  isOverrideActive(dshActive: string): boolean
 } | undefined
 
 /**
@@ -752,10 +759,11 @@ export type CopyKey = keyof typeof zh
 
 /** Translate a copy key; `{name}` placeholders interpolate from `params`. */
 export function t(key: CopyKey, params?: Record<string, string | number>): string {
-  // 1. better-locale override (e.g. ja) wins when an override is active
-  //    and the store has a translation for this (ns, key). The DSH active
-  //    locale is forwarded for forward compatibility (a future mode could
-  //    gate overrides on DSH being 'en'); the current store ignores it.
+  // 1. better-locale override (e.g. ja) wins when an override is active,
+  //    DSH's active locale is 'en' (the override borrows the en slot),
+  //    and the store has a translation for this (ns, key). The store's
+  //    getOverride returns undefined otherwise (no override, DSH on zh,
+  //    or missing key) and the zh/en chain runs.
   const dshActive = localeService?.getSnapshot().active ?? ''
   const override = betterLocaleStore?.getOverride(dshActive, LOCALE_NS, key)
   let text: string | undefined = override
@@ -780,9 +788,14 @@ export function t(key: CopyKey, params?: Record<string, string | number>): strin
 
 /** Whether the active locale is Chinese (used for selectors). */
 export function isZh(): boolean {
-  // An active override is not Chinese — short-circuit so selectors pick
+  // An override is only "effectively active" when DSH is on 'en' (the
+  // override borrows the en slot). While DSH is on 'zh' the override is
+  // inert — the user sees native zh, so isZh() returns true. When an
+  // override is effectively active, the rendered text is neither zh nor
+  // en (it's ja/ko/...), so isZh() returns false to route selectors to
   // the non-zh branch (e.g. date format, pluralization).
-  if (betterLocaleStore?.active !== undefined) return false
+  const dshActive = localeService?.getSnapshot().active ?? ''
+  if (betterLocaleStore?.isOverrideActive(dshActive) === true) return false
   return activeLocale().toLowerCase().startsWith('zh')
 }
 

tests/locales.spec.ts

@@ -113,17 +113,21 @@ describe('locales (DSH i18n following)', () => {
   })
 })
 
-/** Minimal fake of the better-locale override store (the subset t() reads). */
+/** Minimal fake of the better-locale override store (the subset t()/isZh() read). */
 class FakeBetterLocale {
   active: string | undefined = undefined
   private readonly dict: Record<string, Record<string, Record<string, string>>>
   constructor(dict: Record<string, Record<string, Record<string, string>>>) {
     this.dict = dict
   }
-  getOverride(_dshActive: string, ns: string, key: string): string | undefined {
+  getOverride(dshActive: string, ns: string, key: string): string | undefined {
     if (this.active === undefined) return undefined
+    if (dshActive !== 'en') return undefined
     return this.dict[ns]?.[this.active]?.[key]
   }
+  isOverrideActive(dshActive: string): boolean {
+    return this.active !== undefined && dshActive === 'en'
+  }
   subscribe(_listener: () => void): () => void {
     return () => {}
   }
@@ -175,6 +179,23 @@ describe('locales (better-locale override)', () => {
     expect(isZh()).toBe(true)
   })
 
+  it('override is inert while DSH is on zh (override borrows the en slot)', () => {
+    const locale = new FakeLocale()
+    locale.switchTo('zh')
+    attachLocale(locale)
+
+    const betterLocale = new FakeBetterLocale({
+      [LOCALE_NS]: { ja: { explorer: 'エクスプローラー' } },
+    })
+    betterLocale.active = 'ja'
+    attachBetterLocale(betterLocale)
+
+    // Override is set to 'ja' but DSH is on zh — override is inert,
+    // native zh text wins. The user must switch DSH to en to see ja.
+    expect(t('explorer')).toBe('资源管理器')
+    expect(isZh()).toBe(true)
+  })
+
   it('returns to the zh/en chain after detaching the override store', () => {
     const locale = new FakeLocale()
     locale.switchTo('en')