Marc worked on the ash-project/ash repository, delivering robust multi-tenancy support by building Tenant-aware Aggregates and introducing a dedicated Tenant resource. Using Elixir and focusing on backend development, Marc refactored aggregate logic to ensure all data operations respect tenant boundaries, thereby enhancing data isolation and enabling reliable per-tenant aggregation. The technical approach involved encapsulating tenant-scoped logic and tightening tests to validate multi-tenant scenarios, which improved codebase maintainability. By addressing aggregate to_tenant support, Marc resolved issues with aggregation scope, ensuring correct behavior across tenant contexts. The work demonstrated depth in multi-tenancy and testing, resulting in a more robust backend architecture.