SFTP version re-negotiation

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Say you have a client whose initial SSH_FXP_INIT packet says it
implements v3 and a server whose initial SSH_FXP_VERSION packet says
it implements v4 and only v4.  Even if the client additionally
implemented v4, the SSH_FXP_INIT packet only lets you say one version.

My question is...  what, at that point, would you do?  Would you
simply close the channel, recreate it, and send out a SSH_FXP_INIT
packet saying you implement v4?  Or would you send an SSH_FXP_EXTENDED
request to renegotiate with the server to use v4 even if the server
didn't include the 'versions' extension in its SSH_FXP_VERSION packet?

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