  Magnetic reconnection is often invoked to explain the non-thermal radiation
of relativistic outflows, including jets of active galactic nuclei (AGN).
Motivated by the largely unknown plasma composition of AGN jets, we study
reconnection in the unexplored regime of electron-positron-proton (pair-proton)
plasmas with large-scale two-dimensional particle-in-cell simulations. We cover
a wide range of pair multiplicities (lepton-to-proton number ratio
$\kappa=1-199$) for different values of the all-species plasma magnetization
($\sigma=1,3$ and 10) and electron temperature ($\Theta_e\equiv
kT_e/m_ec^2=0.1-100$). We focus on the dependence of the post-reconnection
energy partition and lepton energy spectra on the hot pair plasma magnetization
$\sigma_{e,h}$ (i.e., the ratio of magnetic to pair enthalpy densities). We
find that the post-reconnection energy is shared roughly equally between
magnetic fields, pairs, and protons for $\sigma_{e,h}\gtrsim 3$. We empirically
find that the mean lepton Lorentz factor in the post-reconnection region
depends on $\sigma, \Theta_e$, and $\sigma_{e,h}$ as $\langle \gamma_e-1\rangle
\approx \sqrt{\sigma}(1+4\Theta_e)\left(1+\sigma_{e,h}/30\right)$, for
$\sigma\ge1$. The high-energy part of the post-reconnection lepton energy
distributions can be described by a power law, whose slope is mainly controlled
by $\sigma_{e,h}$ for $\kappa \gtrsim 3-6$, with harder power laws obtained for
higher magnetizations. We finally show that reconnection in pair-proton plasmas
with multiplicities $\kappa \sim 1-20$, magnetizations $\sigma \sim 1-10$, and
temperatures $\Theta_e \sim 1-10$ results in particle power law slopes and
average electron Lorentz factors that are consistent with those inferred in
leptonic models of AGN jet emission.
