Schematic representation of the ^•CN chemical network on interstellar ice surfaces. The figure summarizes the reactions investigated in this work (the hydrogenation of HCN and HNC) together with related processes reported in previous studies (Enrique-Romero et al. 2022; Molpeceres et al. 2024; Enrique-Romero & Lamberts 2024; Enrique-Romero & Lamberts 2025), shown as colored regions. Unless otherwise indicated, radical species have doublet spin multiplicity. Solid arrows denote barrier-less reactions, whereas dashed arrows indicate reactions with an activation barrier. Activation energies are given in kJ mol⁻¹. Arrow colors indicate reaction types: blue for H addition and abstraction, red for reactions with H₂, gray for wHts, and black for other processes (e.g., isomerization or radical-radical reactions). Energies are reported on a per-reaction basis, assuming efficient thermalization on amorphous solid water, such that each activation barrier is referenced to the products of the preceding step.