Fairness is a recurring challenge in grassroots digital infrastructures, where collective action depends on volunteer contributions. This paper presents a study of Foodsharing.de, a grassroots FOSS platform with 185,000 members rescuing and redistributing surplus food. Drawing on 25 interviews and long-term activist involvement, we analyze two justice-oriented features: the Cherry-Picking Rule (distributional fairness) and Commitment Statistics (contributional fairness). We show how these fairness features become deeply entangled in practice and how they operate as policy-in-code, inscribing fairness logics into software and redistributing not only food and labor but also authority within the community. Rather than settling questions of justice, these interventions trigger renewed negotiation across deliberative spaces and everyday coordination, as encoded rules are interpreted, contested, and adapted. Building on these dynamics, we outline governance directions for justice-oriented grassroots infrastructures, highlighting the need for contestability and accountable autonomy to sustain negotiation and align technical change with community legitimacy.

Technology plays a pivotal role in driving transformation through grassroots movements, which operate on a local scale while embracing a global perspective on sustainability. Consequently, research emerged within Sustainable HCI, aiming to derive design principles that can empower these movements to scale their impact. However, a notable gap exists in contributions when addressing scalability of large free and open-source software (FOSS) projects.