Companion
The Mac list is the whole screen while no Mac is chosen, instead of a narrow column beside two panes whose only content was a reminder that nothing had been chosen. Pick one and the three-column layout arrives; collapse the machine column and it stays collapsed next time on that device.
A Mac you have starred, when it is the only one reachable, opens without asking. Anything else still shows the list. Opening a Mac lands on the workspace you were last on there, or its first, so you are not looking at an empty terminal pane while a Mac is connected.
Macs can be renamed on the phone or iPad, and starred. Each row shows the name you gave it, the name the Mac calls itself when the two differ, and the relay it reaches — so one machine paired through a dev relay and a prod relay is finally two rows you can tell apart. The name is yours and stays on your device; the pairing itself is untouched.
Sending diagnostics to the Mac now says what happened. It reports the size once sent, says when no Mac is connected or nothing has been recorded, and gives the reason verbatim when the Mac refuses — including a Mac running a version too old to accept them.