The screen at the front of a room is the one screen in a building that regularly stops a meeting.
Everyone has stood at the front of a room passing a cable around, hunting the adapter that fits this laptop, or waiting while a guest is walked through joining the wifi. The screen at the front is the one screen in the building that regularly stops a meeting.
Ava puts a code and a QR on the screen. Whoever is presenting scans it and casts from where they are sitting. The host sets how long the code lives, it works once, and it can be pointed at one screen or every screen in the room. Nothing is installed on the laptop and no cable changes hands.
It only joins from your own network, and that is enforced rather than assumed: if a device is not on a network you have declared, the join is refused. Every join records which device took the screen, so a room that is misused is answerable rather than mysterious.
A code and a QR on the screen. Scan it and present, from your own seat.
Single use and time limited. The host chooses the window, and a used code is dead.
One screen or every screen in the room, chosen when the code is issued.
Joins only from a network you have declared. No declared network means no joins at all.
Every join is attributable, so an unexplained takeover is not possible.