  The halo-galaxy lensing correlation function or the average tangential shear
profile over sampled halos is a very powerful means of measuring the halo
masses, the mass profile, and the halo-mass correlation function of very large
separations in the linear regime. We reformulate the halo-galaxy lensing
correlation in harmonic space. We find that, counter-intuitively, errors in the
conventionally used flat-sky approximation remain at a % level even at very
small angles. The errors increase at larger angles and for lensing halos at
lower redshifts: the effect is at a few % level at the baryonic acoustic
oscillation scales for lensing halos of $z\sim 0.2$, and comparable with the
effect of primordial non-Gaussianity with $f_{\rm NL}\sim 10$ at large
separations. Our results allow to readily estimate/correct for the full-sky
effect on a high-precision measurement of the average shear profile available
from upcoming wide-area lensing surveys.
