We are tasked with evaluating the definite integral:

$\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \left( \frac{\cos x}{\pi^{-x} + 1} \right) \pi^{-x} \, dx$

Step-by-step approach:

1. Simplifying the integrand: The integrand can be rewritten as follows:

   $\frac{\cos x}{\pi^{-x} + 1} \cdot \pi^{-x} = \frac{\cos x \cdot \pi^{-x}}{\pi^{-x} + 1}$

   This is the form we'll work with for the integral.

2. Symmetry considerations: Since the limits of the integral are symmetric, $[- \frac{\pi}{2}, \frac{\pi}{2}]$, and we have a cosine function, which is an even function ($\cos(-x) = \cos(x)$), we can check if there is symmetry in the denominator. Let’s substitute $x = -t$ in the denominator:

   $\frac{\cos(-t) \cdot \pi^{t}}{\pi^t + 1} = \frac{\cos t \cdot \pi^{t}}{\pi^{t} + 1}$

   The structure of the integral remains the same, suggesting the function is symmetric about $x = 0$, and thus we can exploit the even nature of the function to reduce the integral:

   $2 \int_0^{\frac{\pi}{2}} \frac{\cos x \cdot \pi^{-x}}{\pi^{-x} + 1} \, dx$

3. Solving the integral: Recognizing that the integrand has a fairly complex form, we may need to consider standard techniques such as substitution or numerical evaluation. However, given the structure, it's possible that the problem intends for us to notice the symmetry and special values of the function, leading to a simpler solution through symmetry arguments and known results of integrals involving $\cos x$.

Thus, the value of the integral is likely to be:

$\boxed{0}$

since the integrand's evenness and the properties of cosine over symmetric limits often lead to cancellation.

Would you like further clarification on any part of this solution or details on how the symmetry helps simplify the evaluation?

Here are some related questions for deeper understanding:

1. How does symmetry simplify definite integrals with even or odd functions?
2. Can this integral be evaluated using substitution? If so, what substitution would you use?
3. What are the properties of the cosine function that make it even?
4. Why is exploiting the bounds of integration important for solving this problem?
5. How would this integral change if $\sin x$ were in place of $\cos x$?

Tip: Always check for symmetry (even or odd functions) when the limits of integration are symmetric, as it often simplifies the calculation.