:raw -> :string in sign_buffer(). Something still isn't working correctly.
Switch to OpenSSL::PKey::RSA#ssh_do_sign since Net::SSH did that work for me.
Track client header.
Add Net::SSHD::Packet#payload.
It now is signing the correct data, at least.
Clean up (unused) NEWKEYS handler a bit.
I'm not sure what convinced me that was SHA1, but it is, in fact, SHA256. It works now!
@mac.length -> @mac_length
Start of NEWKEYS handler.
Actually works without my unintentional modifications to net:ssh. Works with normal ssh, too.