The console tab posts to /cmd and throws the response away, so the page stayed
silent whether the command worked, was refused or was just misspelt. Now that
/cmd answers with the command's output, the page keeps a running transcript:
each command echoed after a prompt, then whatever it printed.
The box is a pre element filled through textContent, so nothing the device
prints is taken for markup. It scrolls to the newest line and the input clears
after a send.