When to Stop? An Experimental Study on AI Teachable Agent Stopping Mechanisms and Their Learning Affordance in Mathematics. - Anna Yinqi Zhang; Chenglu Li; Gökhan Gülfidan; Hai Li; Magdalena Castaneda-Rios; Rui Guo 015; Yukyeong Song; Wanli Xing 001 (AIED, 2026)