  We compute the cross section for photons emitted from sea quarks in
proton-nucleus collisions at collider energies. The computation is performed
within the dilute-dense kinematics of the Color Glass Condensate (CGC)
effective field theory. Albeit the result obtained is formally at
next-to-leading order in the CGC power counting, it provides the dominant
contribution for central rapidities. We observe that the inclusive photon cross
section is proportional to all-twist Wilson line correlators in the nucleus.
These correlators also appear in quark-pair production; unlike the latter,
photon production is insensitive to hadronization uncertainties and therefore
more sensitive to multi-parton correlations in the gluon saturation regime of
QCD. We demonstrate that $k_\perp$ and collinear factorized expressions for
inclusive photon production are obtained as leading twist approximations to our
result. In particular, the collinearly factorized expression is directly
sensitive to the nuclear gluon distribution at small $x$. Other results of
interest include the realization of the Low-Burnett-Kroll soft photon theorem
in the CGC framework and a comparative study of how the photon amplitude is
obtained in Lorenz and light-cone gauges.
