In the presence of peroxide,

All the steps are exothermic in $\mathrm{HCl}$ and $\mathrm{HI}$

One of the steps is endothermic in $\mathrm{HCl}$ and HI

$\mathrm{HCl}$ is oxidizing and the HI is reducing

Both $\mathrm{HCl}$ and HI are strong acids