Trident addresses inaccurate rendering-thread identification, resource contention among thread groups, and disconnected CPU, GPU, and memory frequency control. It combines cross-layer thread tracing, reinforcement-learning-based multi-domain governing, and gain-guided scheduling constraints. Evaluation across five phones and multiple application categories shows that Trident preserves Quality of Experience while reducing power consumption by up to 16.8% compared with three state-of-the-art approaches.