The guide said a proxy root like http://localhost:4000/gemini "works the same"
as spelling out /v1beta, but the chat/aux clients only take the native Gemini
adapter when is_native_gemini_base_url() matches the
generativelanguage.googleapis.com host; normalize_gemini_base_url() applies to
the Google host, TTS and the tier probe. Reword the docs to those cases and
tell proxy users to configure an OpenAI-compatible URL. Also note in the
normalize_gemini_base_url docstring that only the last path segment is
inspected and that it does not decide routing.
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