Sharing and multi-tenancy in the schema

If artifacts and conversations can be shared, model sharing explicitly: an owner field plus a shared_with list (of user ids or emails), or a separate shares table with per-grant permissions. Make the sharing rule visible in the data so your access checks (Chapter 11) can evaluate it directly. Nullable "container" references (a document may or may not belong to a project) let the same tables serve both standalone and grouped use.