We provide a holistic routing and wavelength assignment (RWA) solution to a 2-D-torus-based fault-tolerance problem in which an arbitrary bidirectional link (bilink) failure is tolerated. First, we introduce an optimal working lightpath RWA (WRWA) scheme for an N$,times,$ N torus. Then, by observing a uniform pattern by which WRWA arranges working lightpaths through a bilink, we propose a spare lightpath RWA (SRWA) scheme that provisions spare resources to accommodate all traffic originally carried on the bilink subject to failure. The proposed SRWA scheme is at a spare wavelength cost within 1/N of that for the working lightpaths. We show a factor-2 performance guarantee for the proposed SRWA scheme. Finally, we derive a polynomial-time resolvable connection reliability expression for the proposed bilink-failure-free scheme and numerical results show a clear evidence of fault-tolerance capacity improvement.