Zhipu AI (智谱) serves both international users via api.z.ai and
China-based users via open.bigmodel.cn. The domestic endpoint was not
mapped in _URL_TO_PROVIDER, causing Hermes to treat it as an unknown
custom endpoint and fall back to the default 128K context length
instead of resolving the correct 200K+ context via models.dev or the
hardcoded GLM defaults.
This affects users of both the standard API
(https://open.bigmodel.cn/api/paas/v4) and the Coding Plan
(https://open.bigmodel.cn/api/coding/paas/v4).
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