OpenApps: Simulating Environment Variations to Measure UI Agent Reliability - Ullrich, Karen; Su, Jingtong; Shi, Claudia; Subramonian, Arjun; Bar, Amir; Evtimov, Ivan; Tsilivis, Nikolaos; Balestriero, Randall; Kempe, Julia; Ibrahim, Mark (International Conference on Learning Representations, 2026)