Execute action until system beep

I can see how to cause system beep, but I can't see where to find it as a condition to be met... Ideas?

I'm trying to make an Omni Outliner macro to easily send the cursor to the far left hand column and I need to be able signal the macro that the cursor has arrived there...

I can't speak for OO specifically, but generally that type of move is near instantaneous, and so at most I would use a Pause Action of ~0.2 sec.
Adjust as needed to fit your circumstance.

Yeah, I figured I'd need a pause. But am I right that there seems to be no way to set system beep as a condition?

Correct, you cannot detect a system beep (or any sound) happening. Keyboard Maestro has no facility for this, and I doubt it could be done without using private APIs or other system hooks which Keyboard Maestro does not do.