feat(locale): derive the initial Settings language from the browser

A first visit resolved to Chinese regardless of the browser: LocaleService
read `dsh.locale` and fell straight back to `zh` when nothing was stored,
ignoring the languages the browser already states it reads.

The initial locale now resolves through three ordered sources — the persisted
preference, then `navigator` (first entry of the ordered language list whose
primary subtag names a shipped locale, so `zh-Hans-CN` -> zh and `en-GB` ->
en), then `FALLBACK_LOCALE`. An explicit choice still wins and nothing writes
the detected locale back to storage, so "has the user chosen?" stays a
question only the stored value answers.

Specs asserting the shipped Chinese copy now state the browser they assume:
the web e2e scenarios open their page with `locale: ZH_BROWSER_LOCALE`, and
package specs pin it through the new `pinBrowserLanguages` test helper.
`settings-chrome.e2e.ts` gains an English-browser scenario as the
assembled-app proof.

packages/client/locale/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/client/locale/README.md
-README.md: c2adbcabc77def740094288da4643032873aa5b8
-README.zh.md: c6ecb31e21d7513a4e7d579b17588107ccd7ea59
+README.md: 7f780092af9bc7079cc5080c06e986bef2dfdbce
+README.zh.md: 62c037977115d33b834fe60b042431e44d208524

packages/client/locale/README.md

@@ -2,7 +2,7 @@
 
 English | [中文](README.zh.md)
 
-Locale plugin: LocaleService — the browser locale preference (`zh`/`en`, persisted under `dsh.locale`; `locale/change` fires on switches only) plus the ns×locale dictionary registry (typed `register(ns, {zh, en})` checked against `LocaleNamespaceMap`, `bind(ns)`→`TranslateNS<ns>`; lookup chain ns → common → zh → key). The service implements the slot system's `LocaleFace` and installs itself through `ctx.slots.installLocale`, backing the framework-injected `t` standard seat (`Translate`/`TranslateNS` are ui-slots types; import them from there — this package only re-exports for dictionary owners' convenience).
+Locale plugin: LocaleService — the browser locale preference (`zh`/`en`, persisted under `dsh.locale`; with nothing persisted a fresh browser opens in the language `navigator` asks for — matched on the primary subtag, `zh` when it asks for none this app ships; `locale/change` fires on switches only) plus the ns×locale dictionary registry (typed `register(ns, {zh, en})` checked against `LocaleNamespaceMap`, `bind(ns)`→`TranslateNS<ns>`; lookup chain ns → common → zh → key). The service implements the slot system's `LocaleFace` and installs itself through `ctx.slots.installLocale`, backing the framework-injected `t` standard seat (`Translate`/`TranslateNS` are ui-slots types; import them from there — this package only re-exports for dictionary owners' convenience).
 
 ## Model Experience
 

packages/client/locale/README.zh.md

@@ -2,7 +2,7 @@
 
 [English](README.md) | 中文
 
-locale 插件：LocaleService——浏览器 locale 偏好（`zh`／`en`，以 `dsh.locale` 持久化；`locale/change` 仅在切换语言时触发），加上 ns×locale 字典注册表（类型化 `register(ns, {zh, en})` 按 `LocaleNamespaceMap` 校验，`bind(ns)`→`TranslateNS<ns>`；查找链 ns → common → zh → key）。该服务实现 slot 系统的 `LocaleFace` 并经 `ctx.slots.installLocale` 自行安装，支撑框架注入的 `t` 标准席位（`Translate`／`TranslateNS` 是 ui-slots 的类型；请从那里导入——本包的再导出仅为字典所有者提供便利）。
+locale 插件：LocaleService——浏览器 locale 偏好（`zh`／`en`，以 `dsh.locale` 持久化；未持久化偏好时，全新浏览器以 `navigator` 请求的语言开场——按主子标签匹配，若其请求的语言本应用都不提供则为 `zh`；`locale/change` 仅在切换语言时触发），加上 ns×locale 字典注册表（类型化 `register(ns, {zh, en})` 按 `LocaleNamespaceMap` 校验，`bind(ns)`→`TranslateNS<ns>`；查找链 ns → common → zh → key）。该服务实现 slot 系统的 `LocaleFace` 并经 `ctx.slots.installLocale` 自行安装，支撑框架注入的 `t` 标准席位（`Translate`／`TranslateNS` 是 ui-slots 的类型；请从那里导入——本包的再导出仅为字典所有者提供便利）。
 
 ## 模型体验
 

packages/client/locale/src/client/index.ts

@@ -83,7 +83,7 @@ declare module 'cordis' {
   }
 }
 
-/** Fallback locale consulted after the active locale misses (also the default). */
+/** Fallback locale consulted after the active locale misses (also the last-resort initial locale). */
 export const FALLBACK_LOCALE: LocaleId = 'zh'
 
 /** Shared namespace for shell-level texts. */
@@ -123,7 +123,7 @@ export class LocaleService {
    */
   constructor(ctx: Context) {
     this.ctx = ctx
-    this.snapshot = Object.freeze({ active: restorePreference(), locales: LOCALES, revision: 0 })
+    this.snapshot = Object.freeze({ active: resolveInitialLocale(), locales: LOCALES, revision: 0 })
   }
 
   /**
@@ -288,17 +288,45 @@ export class LocaleService {
   }
 }
 
-/** Read the persisted locale id; unknown or unreadable values fall back to zh. */
-function restorePreference(): LocaleId {
+/**
+ * The locale a fresh service opens with: an explicit preference the user
+ * already chose wins over the browser's own language, which in turn wins over
+ * {@link FALLBACK_LOCALE} (non-browser boots and browsers set to a language
+ * this app does not ship).
+ */
+function resolveInitialLocale(): LocaleId {
+  return restorePreference() ?? detectBrowserLocale() ?? FALLBACK_LOCALE
+}
+
+/** Read the persisted locale id; unknown or unreadable values read as no preference. */
+function restorePreference(): LocaleId | undefined {
   // Non-browser runs (node e2e booting the client tree) have no localStorage.
-  if (typeof localStorage === 'undefined') return FALLBACK_LOCALE
+  if (typeof localStorage === 'undefined') return undefined
   try {
     const stored = localStorage.getItem(STORAGE_KEY)
     if (stored === 'zh' || stored === 'en') return stored
   } catch {
-    // Storage access can throw (privacy mode); the default below covers it.
+    // Storage access can throw (privacy mode); an unreadable store simply
+    // records no preference, and the browser language decides instead.
   }
-  return FALLBACK_LOCALE
+  return undefined
+}
+
+/**
+ * The first shipped locale the browser asks for, matched on the primary
+ * subtag so every regional variant lands on its language (`zh-Hans-CN` -> zh,
+ * `en-GB` -> en). `navigator.language` trails the ordered `languages` list
+ * because a browser may expose only the former.
+ */
+function detectBrowserLocale(): LocaleId | undefined {
+  // Non-browser runs (node e2e booting the client tree) have no navigator.
+  if (typeof navigator === 'undefined') return undefined
+  for (const tag of [...navigator.languages, navigator.language]) {
+    const primary = tag.toLowerCase().split('-')[0]
+    const match = LOCALES.find(locale => locale.id === primary)
+    if (match) return match.id
+  }
+  return undefined
 }
 
 /** Persist the locale id; storage failures are non-fatal (preference resets next boot). */

packages/client/locale/tests/apply.spec.ts

@@ -2,7 +2,7 @@
  * Language row registration, snapshot projection into the row store, and
  * recovery after an HMR collapse of the declaring entry. */
 import { Context } from 'cordis'
-import { describe, expect, it } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { SlotsService } from '@deepseek-ai/dsh-client-runtime/client'
 import { apply, inject, SETTINGS_NS } from '@deepseek-ai/dsh-client-locale/client'
 import type { LanguageRowInjected, LocaleService } from '@deepseek-ai/dsh-client-locale/client'
@@ -36,6 +36,16 @@ function faceOf(slots: SlotsService) {
 }
 
 describe('locale apply', () => {
+  // A fresh service opens in the browser's language, so these wiring specs
+  // pin one to keep their zh baseline independent of the test environment.
+  beforeEach(() => {
+    vi.stubGlobal('navigator', { languages: ['zh-CN'], language: 'zh-CN' })
+  })
+
+  afterEach(() => {
+    vi.unstubAllGlobals()
+  })
+
   it('declares the slot service', () => {
     expect(inject).toEqual(['slots'])
   })

packages/client/locale/tests/locale.spec.ts

@@ -1,5 +1,5 @@
 // @vitest-environment jsdom
-import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { Context } from 'cordis'
 import type { LocaleSnapshot } from '@deepseek-ai/dsh-client-locale/client'
 import { LocaleService, STORAGE_KEY } from '@deepseek-ai/dsh-client-locale/client'
@@ -11,9 +11,20 @@ const make = (): { ctx: Context; svc: LocaleService; events: LocaleSnapshot[] }
   return { ctx, svc: new LocaleService(ctx), events }
 }
 
+/** Pin the browser environment a fresh service reads its initial locale from. */
+const stubLanguages = (...tags: string[]): void => {
+  vi.stubGlobal('navigator', { languages: tags, language: tags[0] ?? '' })
+}
+
 describe('LocaleService', () => {
   beforeEach(() => {
     localStorage.clear()
+    // A Chinese browser is the baseline these specs assert their zh state on.
+    stubLanguages('zh-CN')
+  })
+
+  afterEach(() => {
+    vi.unstubAllGlobals()
   })
 
   it('translates through the active-locale -> zh -> key chain', () => {
@@ -132,23 +143,45 @@ describe('LocaleService', () => {
     expect(() => { svc.setLocale('fr') }).toThrow('not registered')
   })
 
-  it('restores a persisted locale and falls back to zh on garbage', () => {
+  it('restores a persisted locale over the browser language, and garbage reads as no preference', () => {
     localStorage.setItem(STORAGE_KEY, 'en')
     expect(make().svc.getLocale().active).toBe('en')
     localStorage.setItem(STORAGE_KEY, 'fr')
     expect(make().svc.getLocale().active).toBe('zh')
   })
 
-  it('runs without localStorage (node boots): defaults on read, no-op on write', () => {
+  it('opens in the browser language when nothing is persisted, matching regional variants on their primary subtag', () => {
+    stubLanguages('en-GB', 'zh-CN')
+    expect(make().svc.getLocale().active).toBe('en')
+    stubLanguages('zh-Hant-TW')
+    expect(make().svc.getLocale().active).toBe('zh')
+    // An unshipped language walks the list to the first one this app ships.
+    stubLanguages('fr-FR', 'en-US')
+    expect(make().svc.getLocale().active).toBe('en')
+    // Only `language` populated (browsers that expose no ordered list).
+    vi.stubGlobal('navigator', { languages: [], language: 'en-US' })
+    expect(make().svc.getLocale().active).toBe('en')
+    // No shipped language anywhere in the browser's preferences: zh remains
+    // the product default rather than an arbitrary near-match.
+    stubLanguages('fr-FR', 'de')
+    expect(make().svc.getLocale().active).toBe('zh')
+  })
+
+  it('runs without localStorage or navigator (node boots): defaults on read, no-op on write', () => {
     vi.stubGlobal('localStorage', undefined)
-    try {
-      const { svc } = make()
-      expect(svc.getLocale().active).toBe('zh')
-      svc.setLocale('en')
-      expect(svc.getLocale().active).toBe('en')
-    } finally {
-      vi.unstubAllGlobals()
-    }
+    vi.stubGlobal('navigator', undefined)
+    const { svc } = make()
+    expect(svc.getLocale().active).toBe('zh')
+    svc.setLocale('en')
+    expect(svc.getLocale().active).toBe('en')
+  })
+
+  it('keeps the browser language out of the way once a preference exists', () => {
+    stubLanguages('en-US')
+    const { svc } = make()
+    svc.setLocale('zh')
+    expect(localStorage.getItem(STORAGE_KEY)).toBe('zh')
+    expect(make().svc.getLocale().active).toBe('zh')
   })
 
   it('exposes the two shipped locales with self-described labels', () => {