CooperBench: Why Coding Agents Cannot be Your Teammates Yet. - Arpandeep Khatua; Hao Zhu; Peter Tran; Arya Prabhudesai; Frederic Sadrieh; Johann K. Lieberwirth; Xinkai Yu; Yicheng Fu; Michael J. Ryan; Jiaxin Pei; Diyi Yang (CoRR, 2026)