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