Constitutional Arms Races in the Public Goods Game: Co-Evolving LLM Constitutions Under Cooperation-Defection Pressure. - Ujwal Kumar; Arth Singh; Hershraj Niranjani; Machiko Hirota; Takehiro Takayanagi; Alice Saito; Eiji Kamioka; Phan Xuan Tan (CoRR, 2026)