LOS ANGELES (AP) — Jurors in a landmark social media case that seeks to hold tech companies responsible for harms to children got their first glimpse into what will be a lengthy trial characterized by dueling narratives from the plaintiffs and the two remaining defendants, Meta and YouTube. At the core of the Los Angeles case is a 20-year-old identified only by the initials “KGM,” whose case could determine how thousands of similar lawsuits will play out. KGM and the cases of two other a...