KnowGuard: Knowledge-Driven Abstention for Multi-Round Clinical Reasoning - Dang, Xilin; Chen, Kexin; Su, Xiaorui; Noori, Ayush; Arango, Iñaki; Vittor, Lucas; XINYI, LONG; Du, Yuyang; Zitnik, Marinka; Heng, Pheng-Ann (International Conference on Learning Representations, 2026)