How do I make sure AI can only see the documents each employee is already allowed to see?

Make AI act as the signed-in user, never a super-user: Microsoft 365 access runs through each person's own sign-in (per-user OAuth sessions), on-prem SharePoint Server is read through Kerberos delegation so existing SharePoint permissions decide what AI can see, and identity comes from Microsoft Entra (SSO and SCIM provisioning). Fix a permission once, at the source, and AI inherits the fix.