  We derive the medium-induced, coherent gluon radiation spectrum associated
with the hard forward scattering of an energetic parton off a nucleus, in the
saturation formalism and within the Gaussian approximation for the relevant
correlators of Wilson lines. The calculation reproduces the simple expression
for the spectrum previously obtained in the opacity expansion formalism, and
rigorously specifies its validity range. The connection between the
calculations in the opacity expansion and saturation formalisms is made
apparent. This study may serve as a first step in order to implement
consistently induced coherent energy loss and gluon shadowing in
`saturation-based models' of hadron nuclear suppression in proton-nucleus
collisions.
