What is multi-tenant isolation?
Multi-tenant isolation means every row is owned by a tenant and readable only through that tenant’s identity. Here the tenant is always derived from the authenticated API key and never read from a request body, and access is default-deny at the database level rather than filtered in application code.
Why it matters
Application-level filtering fails open — one forgotten WHERE clause is a cross-tenant leak. Default-deny at the row level fails closed: a query that forgets the tenant returns nothing instead of everything.