Quagmires in SFT-RL Post-Training: When High SFT Scores Mislead and What to Use Instead - Kang, Feiyang; Kuchnik, Michael; Padthe, Karthik; Vlastelica, Marin; Jia, Ruoxi; Wu, Carole-Jean; Ardalani, Newsha (International Conference on Learning Representations, 2026)