LOS ANGELES — In closing arguments for the first social media addiction trial to make tech giants face a jury, the plaintiff's lawyer lambasted social platforms for profiting from users' attention, likening their features to a Trojan horse. The plaintiff, identified in court as Kaley and in documents by her initials, K.G.M., is at the center of a bellwether case that could set a legal precedent for whether social media platforms are responsible for causing mental health issues in children. Her