Workspace isolation, enforced at the database
Every table that holds user data (campaigns, leads, conversations, settings, audit logs) has row-level access policies that scope reads and writes to members of the owning workspace. The check runs inside the database itself, not just in application code. A bug in our app layer can't override it; a leaked database key can't override it. This is the defense-in-depth posture we wanted, so we paid the up-front cost of writing the policies.