Itās quite simple, heās the foreign minister. Heās responsible for it. Heās got the same authority and power Zarif had in drafting the agreement.
Also, please spare me with him being a ābrilliantā strategist, heās not. During the negotiations, before they attacked Iran, Araghchi made a public interview in english saying: āif they kill our leader, weāll just replace him with a new oneā instead of saying that weāll burn the region into fire. What kind of message does that give? That itās fine to kill our leader. A little after that they betrayed the negotiations and killed the leader. So no, heās absolutely NOT a brilliant diplomat.
And people have every right to be angry at him.