My response is:
?
and go back to work. I feel a bit mean if they are exceedingly polite and Start with "Good Morning" I might give them a Hi in that case.
Either way I go back to what I was doing until I come to a convenient stopping point, typically between 1 and 5 minutes.
One of my biggest annoyances.
I have gotten in the habit of just responding "yo" and going back to whatever I was doing.
Could be minutes to an hour before I come back to the chat