Update for anyone finding this later. Our unit has the remote on/off terminal, the installer fitted a two wire cable to it on Thursday. The plug now just closes a dry contact, I took the relay output out of the plug housing into a small DIN box. The run status comes back on a spare GPIO as ac.running.
The rule fired for real yesterday when the room hit 27.4, the AC started and I got the notification. One thing I had wrong at first: I had turned off Ask before running on the switch, put it back on after Rachel’s comment about clicking things by accident.