In an ionic crystal with a rock salt (\(\text{NaCl}\)) lattice, anions (\(\text{X}^-\)) of radius \(r_-\) sit at the corners and face centers of a cubic unit cell of edge length \(L\), and cations (\(\text{M}^+\)) of radius \(r_+\) sit at the midpoints of the cell edges, as shown for one face of the unit cell. In the limiting case, the anions touch one another along each face diagonal, and each cation just touches the two anions on either side of it along the cell edge. What is the minimum cation-to-anion radius ratio \(\dfrac{r_+}{r_-}\) for which this octahedral arrangement is stable?