使用OAuth认证时，调用coze.chat.retrieve()函数会保错：认证不合法

使用OAuth认证时，调用coze.chat.retrieve()函数会保错：cozepy.exception.CozeAPIError: code: 4100, msg: authentication is invalid

Start by reproducing the OAuth flow with the coze.chat.retrieve() entry point described in the issue and inspect how authentication is passed to the API. Compare the failing request and error response with the SDK's OAuth handling. Done means OAuth-authenticated retrieval succeeds without the 4100 authentication error.

Written by the indexing model from the issue text.