Given that it is intended as a trap, I would presume one of the Aes Sedai present at the meeting that is seen in the Bloodline History was secretly a Dark Friend, and Moridin directly states it is a Sa'angreal for the True Power when he picks it up and makes it glow red, At this point I think it...
Well the Chodean Kal are the most powerful Sa'angreal Created IIRC, and He may have used Callandor..I just don't think he did because it has flaws.
My Guess on the battle was Lews Therin crafting the 7 seals using Disks as focuses while the companions and whatever Mundane forces existed held...