Using ssh.Unmarshal since commit c11ed6a015 means the "shell" payload should be propely formatted, with a specified string length. Otherwise, when attempting to connect, you'll see this message in the gokrazy stderr:
ssh: parse error in message type 0
that's because in x/crypto/ssh, the parseString() method expects a length before the string. If length is 0, there will be remaining unparsed data, and an error.
