Asking how a “rational” agent reasons about the actions of another “rational” agent is analogous to asking whether a formal logic can prove statements about that logic. I suggest you look into the extensive literature on completeness, incompleteness, and hierarchies of logics. It may be that there are situations such that it is impossible for a “rational” agent to prove what another, equally-rational agent will conclude in that situation.
Asking how a “rational” agent reasons about the actions of another “rational” agent is analogous to asking whether a formal logic can prove statements about that logic. I suggest you look into the extensive literature on completeness, incompleteness, and hierarchies of logics. It may be that there are situations such that it is impossible for a “rational” agent to prove what another, equally-rational agent will conclude in that situation.