I want to map a bus platform (as an area) directly adjacent to a pedestrian area.
In the desired configuration, I would create two contiguous areas, as this picture shows. Along with ordinary footways to route users properly.
OSM Inspector flags a warning here (duplicated edge areas), presumably because both areas have nodes A-B-C-D-E-F-G in common.
My question is: Is this layout really incorrect? Should I put some empty space between the two areas instead?
Is the actual road in the white but in the bottom in your diagram?
Yes, there is a road south of the platform (and unconnected to it, if that was the concern).
That is a bogus warning. Mapping it as multipolygons would not help.
I recommend using JOSM validator (they used to report such case as error, but I think that it is now fixed).
but here specifically: are you sure that platform is not part of the square? If I would be mapping it, then
highway=pedestrian area=yes would include platform area.