Smooth Operator: Smooth Verifiable Reward Activates Spatial Reasoning Ability of Vision-Language Model. - Siwen Jiao; Tianxiong Lv; Kangan Qian; Chenxu Zhao; Xiuyuan Zhu; Tianlun Li; Xiaolong Cheng; Jinyu Li; Zhihao Liao 005; Yang Cai (CoRR, 2026)