A cart on a horizontal track accelerates to the right with a constant acceleration of magnitude \(a\). A small block of mass \(m\) is held against the front face of the cart, which is inclined at an angle \(\theta\) above the horizontal (\(0 < \theta \le 90^\circ\)). The coefficient of static friction between the block and the inclined face is \(\mu_s\), such that the minimum acceleration required to prevent the block from slipping down the face is given by:
\[ a_{\text{min}} = g\left(\dfrac{\sin\theta - \mu_s \cos\theta}{\cos\theta + \mu_s \sin\theta}\right) \]
Which of the following correctly describes the limiting behavior of \(a_{\text{min}}\) as the face becomes vertical (\(\theta \to 90^\circ\)), and correctly identifies the physical roles of the forces exerted by the face on the block?