That's a straw man argument now... How about just a quick look at the wall and how it's detailed? A couple of hours and a thumbs up to the contractor, we aren't talking thousands of dollars here...
Just put on your drawings that the stair is supporting the wall. These drawings should go with the city and a contractor should be able to get a copy if they're doing renos.
Aseur: Removing part of non-critical building element (a handrail, roof/wall panel, light pole, downspout, drain pipe...) is quite common/frequent at industry settings, in which the remove of a stair (commonly known as a service element rather than structural element) is usually expected/considered to be "a next day job", no engineer, and or permit required.
I don't think utilizing the stair to support the wall can't be done, albeit deviating from the common practice/thinking, any deviation from the common practice can be an engineering innovation too. The important thing is, to make it known up front (not a hidden surprise to anybody), rather that just say it is the next guy's problem; or design it in a way that it's importance can be identified by a simple visual inspection (a solid concrete stair in this case, or rigid/stiff connections between the wall and stair be the other). Care needs to be in our mind.
