Spin is not specified in control generator or in geometry.in
The absence of the spin keyword is a key omission and should be enabled.
The tricky part is that with spin enabled, the user will necessarily have to return to the geometry.in file in a follow-up step, in order to place initial_moment tags for certain atoms.
"add initial_moment" should be one of the options available in the geometry builder.
Additionally, for the "simple workflow":
If a geometry.in file did not include initial_moment statements but the control builder step added spin, then after finishing the control.in step the geometry.in builder should reopen and demand that at least one initial_moment tag be specified.
The initial_moment field can also be added for all atoms, just with zero as default for any atom for which the moment is not hand-specified. But the initial_moment option should be there for spin collinear calculations, and it should bve required.