In the end of PoD, ch.14. Maybe Osan'gar, who just left the tent before Narishma, eavesdropped on them and quickly placed the additonal traps on Callandor to spoil Rand's plan and kill Narishma. On the other hand, if he heard about the wards & Rand's instructions to avoid them, he should have been able to take Callandor for himself (except if Rand directly had to show Narishma special weaves to dispel the traps on Callandor, which Osan'gar didn't see).

Otherwise, I don't think we have enough clues to figure this out for sure.