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.
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