How to transfer files from one SSH session to another

其实是类似于xftp的一个特性。可以不需要先拷贝到本机设备再传输到对端，所以一直没法完全替代xftp，与xshell等终端相比太甜品了。

The issue requests an XFTP-like feature for transferring files directly between two SSH sessions without staging them on the local device. No file, test, or entry point is named; first locate the session and file-transfer code and establish the expected remote-to-remote behavior. Done means the transfer works between the two sessions without a local intermediate copy.

Written by the indexing model from the issue text.