No role and no access_level. A project grant is admission; an external guest holds no org role, so there is nothing to choose (spec §3.2's ruling).
Successful Response
The invite plus its one-time link.
The link IS the delivery mechanism — PR3 ships no SMTP for project invites (spec §10's flow is link-first and hermetic; council ruling D2). Resend returns a fresh one because it rotates the token, so the previous link is dead and rendering it would hand the admin a URL that no longer works.