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.

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

@@ -315,13 +315,20 @@ function restorePreference(): LocaleId | 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.
+ * `en-GB` -> en). `window` is the browser test, not `navigator`: Node exposes
+ * a global `navigator` reporting the machine's own language, which would
+ * otherwise decide the locale for non-browser runs (node e2e booting the
+ * client tree). `navigator.language` trails the ordered `languages` list and
+ * covers its absence on hosts that expose only the single tag.
  */
 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]) {
+  if (typeof window === 'undefined') return undefined
+  /* oxlint-disable-next-line typescript/no-unnecessary-condition --
+   * The DOM lib types `languages` as always present; embedders and older
+   * WebViews ship a Navigator without it, and spreading undefined would
+   * throw at boot. Same environment-boundary distrust as the localStorage
+   * guards below. */
+  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

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

@@ -11,7 +11,13 @@ 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. */
+/**
+ * Pin the browser environment a fresh service reads its initial locale from.
+ * This package's own specs stub the globals directly instead of using
+ * `usePinnedBrowserLanguages` (dsh-client-test-runtime): they need the shapes
+ * that helper deliberately cannot express — a missing `languages` list, a
+ * list decoupled from `language`, and a non-browser run with no `window`.
+ */
 const stubLanguages = (...tags: string[]): void => {
   vi.stubGlobal('navigator', { languages: tags, language: tags[0] ?? '' })
 }
@@ -158,18 +164,24 @@ describe('LocaleService', () => {
     // 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).
+    // Only `language` populated: an empty ordered list, and a host that
+    // exposes no `languages` property at all.
     vi.stubGlobal('navigator', { languages: [], language: 'en-US' })
     expect(make().svc.getLocale().active).toBe('en')
+    vi.stubGlobal('navigator', { 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', () => {
+  it('runs outside a browser (node boots): the fallback decides, the machine language does not, writes no-op', () => {
     vi.stubGlobal('localStorage', undefined)
-    vi.stubGlobal('navigator', undefined)
+    vi.stubGlobal('window', undefined)
+    // Node exposes its own global navigator; without a window it must not
+    // reach the resolution at all.
+    stubLanguages('en-US')
     const { svc } = make()
     expect(svc.getLocale().active).toBe('zh')
     svc.setLocale('en')