One can show that for the phase difference $\Delta$ between the two wave functions (slit 1 and slit 2) it holds the first equality on the LHS
$$\Delta=\oint_{\partial\Omega} \vec{A}\overset{!}{=}\int_\Omega \nabla\times \vec{A}=\int_\Omega \vec{B}=\Phi_m$$
This is then used to proof a physically important result, namely that the phase difference is non-vanishing, because there is a flux through $\Omega$ due to the solenoid. There are issues with this.
I'm not a mathematician, but I would never use Stokes here. There is a huge singularity inside $\Omega$ $$\vec{A}_{solenoid}\propto\frac{\hat{\phi}}{r}$$
I'm sure there is a more formal argument than using stokes here?