fix(locale): gate browser detection on window and tolerate a missing languages list

Node >= 21 exposes a global `navigator` reporting the machine's own language,
so gating detection on `navigator` let a non-browser boot of the client tree
resolve to `en` instead of the documented fallback; `window` is the browser
test. `navigator.languages` is spec-required but absent on some embedders and
older WebViews, where spreading it would throw at boot, so the walk tolerates
its absence and `navigator.language` covers that host.

The per-spec pin boilerplate collapses into one suite-level
`usePinnedBrowserLanguages('zh-CN')`, which owns the rationale in
dsh-client-test-runtime, and the English-browser e2e scenario now clears the
console warnings channel too — its page has no closing inventory spec.

.agents/notes/implemented/feature/2026-07-31-browser-derived-initial-locale.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 .agents/notes/implemented/feature/2026-07-31-browser-derived-initial-locale.md
-2026-07-31-browser-derived-initial-locale.md: 7668171f32642248cc0be92741eb3dc90e0669cc
-2026-07-31-browser-derived-initial-locale.zh.md: 568737285e3c00d6c9792a0e6e79e38428db18c3
+2026-07-31-browser-derived-initial-locale.md: 0c49a6bbfec0ab33a5aa3ce53dde0cac747f3816
+2026-07-31-browser-derived-initial-locale.zh.md: c013d24dcd3bb49d176eaddd42ff41dde320ff1f

.agents/notes/implemented/feature/2026-07-31-browser-derived-initial-locale.md

@@ -12,7 +12,9 @@ The Settings Language row opened every first visit in Chinese: `LocaleService` r
 
 **The initial locale resolves through three ordered sources: the persisted preference, then the browser, then `FALLBACK_LOCALE`.** `resolveInitialLocale()` in `packages/client/locale/src/client/index.ts` runs at service construction and is the only place the order is expressed; `restorePreference()` now returns `LocaleId | undefined` (an absent, unparseable, or unreachable store reads as *no preference*) so the next source can speak.
 
-**Browser matching is on the primary subtag, over the ordered list.** `detectBrowserLocale()` walks `[...navigator.languages, navigator.language]` and returns the first entry whose primary subtag names a shipped locale, so `zh-Hans-CN` and `zh-TW` both land on `zh` and `en-GB` on `en`, while a browser asking only for languages this app does not ship (`fr`, `de`) yields nothing and leaves `FALLBACK_LOCALE` in charge. `navigator.language` trails the list because a browser may expose only the former; a runtime without `navigator` at all (node booting the client tree) resolves to the fallback like any unresolvable case.
+**Browser matching is on the primary subtag, over the ordered list.** `detectBrowserLocale()` walks `[...(navigator.languages ?? []), navigator.language]` and returns the first entry whose primary subtag names a shipped locale, so `zh-Hans-CN` and `zh-TW` both land on `zh` and `en-GB` on `en`, while a browser asking only for languages this app does not ship (`fr`, `de`) yields nothing and leaves `FALLBACK_LOCALE` in charge. `navigator.language` trails the list and covers its absence on hosts that ship a Navigator without `languages` — the DOM lib types it as always present, so that tolerance carries a narrow lint exception, the same environment-boundary distrust the `localStorage` guards already express.
+
+**`window`, not `navigator`, is the browser test.** Node ≥ 21 exposes a global `navigator` reporting the machine's own language (`en-US` on the CI runners), so gating on `navigator` would have let a node boot of the client tree resolve to `en` instead of the documented fallback. Gating on `window` keeps every non-browser run on `FALLBACK_LOCALE`.
 
 **An explicit choice is permanent.** `setLocale` persistence is untouched, and the persisted value is consulted first, so a user who picked a language keeps it even when travelling between browser profiles or system languages. Nothing writes the detected locale back to storage: detection is re-derived every boot and stays invisible to the "has the user chosen?" question.
 
@@ -30,5 +32,5 @@ The Settings Language row opened every first visit in Chinese: `LocaleService` r
 
 - A first visit from an English browser lands in English, and the Language row still shows the same two self-described options, so the escape hatch is unchanged in either direction.
 - `FALLBACK_LOCALE` narrows to its real job — the dictionary fallback and the no-signal answer — and stops standing in for "the user has not chosen".
-- Tests that construct a `LocaleService` under jsdom now depend on the environment's `navigator`: the package specs stub it (`zh-CN` as the baseline; the detection spec varies it), and any future spec asserting a default must pin one too.
+- Tests that construct a `LocaleService` under jsdom now depend on the environment's `navigator`: specs asserting localized copy declare their browser with one suite-level `usePinnedBrowserLanguages('zh-CN')` (dsh-client-test-runtime), and any future spec asserting a default must do the same. This package's own specs stub the globals directly, because they need shapes the helper deliberately cannot express (absent `languages`, a list decoupled from `language`, no `window` at all).
 - Detection cost is one array walk per service construction, and no storage write, so boot behavior and the persisted-state surface are unchanged.

.agents/notes/implemented/feature/2026-07-31-browser-derived-initial-locale.zh.md

@@ -12,7 +12,9 @@ Status: implemented
 
 **初始 locale 依次经三个来源解析：已持久化的偏好、浏览器、`FALLBACK_LOCALE`。** `packages/client/locale/src/client/index.ts` 中的 `resolveInitialLocale()` 在服务构造时运行，是这一顺序的唯一表达处；`restorePreference()` 现在返回 `LocaleId | undefined`（存储项缺失、无法解析或不可访问，一律读作*没有偏好*），后一个来源才有开口的机会。
 
-**浏览器匹配按主子标签进行，且遍历有序列表。** `detectBrowserLocale()` 遍历 `[...navigator.languages, navigator.language]`，返回主子标签命中已提供 locale 的首个条目，因此 `zh-Hans-CN` 与 `zh-TW` 同归 `zh`、`en-GB` 归 `en`；而只请求本应用不提供的语言（`fr`、`de`）的浏览器则什么都匹配不到，交由 `FALLBACK_LOCALE` 接管。`navigator.language` 排在列表之后，因为有的浏览器只暴露前者；完全没有 `navigator` 的运行环境（node 启动客户端树）与任何无法解析的情形一样落到回落值。
+**浏览器匹配按主子标签进行，且遍历有序列表。** `detectBrowserLocale()` 遍历 `[...(navigator.languages ?? []), navigator.language]`，返回主子标签命中已提供 locale 的首个条目，因此 `zh-Hans-CN` 与 `zh-TW` 同归 `zh`、`en-GB` 归 `en`；而只请求本应用不提供的语言（`fr`、`de`）的浏览器则什么都匹配不到，交由 `FALLBACK_LOCALE` 接管。`navigator.language` 排在列表之后，并兜住那些 Navigator 上没有 `languages` 的宿主——DOM 库把它标注为必然存在，所以这份容忍带一条窄口径 lint 例外，与 `localStorage` 守卫表达的环境边界不信任同源。
+
+**判定浏览器用的是 `window` 而非 `navigator`。** Node ≥ 21 暴露全局 `navigator` 并报告机器自身语言（CI runner 上是 `en-US`），因此以 `navigator` 把关会让 node 启动客户端树时解析成 `en`，而非文档约定的回落值。以 `window` 把关可使所有非浏览器运行都停留在 `FALLBACK_LOCALE`。
 
 **显式选择是永久的。** `setLocale` 的持久化未作改动，且持久化值最先被查询，因此选过语言的用户即便在不同浏览器配置或系统语言之间辗转也保留原选择。没有任何代码把探测到的 locale 写回存储：探测在每次启动时重新推导，对"用户是否做过选择"这一问题始终不可见。
 
@@ -30,5 +32,5 @@ Status: implemented
 
 - 来自英文浏览器的首访落在英文界面，而语言行依然呈现同样两个以自身语言自述的选项，两个方向的脱身通道都未改变。
 - `FALLBACK_LOCALE` 收窄回它真正的职责——字典回落与无信号时的答案——不再兼职充当"用户尚未选择"。
-- 在 jsdom 下构造 `LocaleService` 的测试现在依赖环境的 `navigator`：包内测试对其打桩（以 `zh-CN` 为基线，探测用例则逐个变换），今后任何断言默认值的用例同样必须钉住它。
+- 在 jsdom 下构造 `LocaleService` 的测试现在依赖环境的 `navigator`：断言本地化文案的用例以一行套件级 `usePinnedBrowserLanguages('zh-CN')`（dsh-client-test-runtime）声明其浏览器，今后任何断言默认值的用例同样如此。本包自己的用例直接给全局打桩，因为它们需要该 helper 刻意不表达的形状（`languages` 缺失、列表与 `language` 解耦、完全没有 `window`）。
 - 探测的代价是每次服务构造遍历一次数组，且不写存储，因此启动行为与持久化状态面均无变化。