Early-stage decisions in construction projects are critical for circularity and long-term sustainability, yet often delayed due to fragmented data and limited decision support. This study explores how cooperative digital environments can improve early decision-making in circular construction. Based on a case study with architecture and construction management students, it applies the Recognition-Primed Decision model to examine how teams navigate uncertainty, material reuse, and sustainability trade-offs. Findings highlight the need for structured frameworks, integrated data platforms, and greater trust in digital tools such as large language models. The paper proposes a practice-oriented framework combining visualization, scenario simulation, and interdisciplinary collaboration. Rather than removing uncertainty, it helps professionals manage it through iterative learning and cooperative use of AI tools.