Reuse an authorized session after a completed invitation exchange

After a one-time invitation exchange has completed, an invitation landing route should prefer an existing authenticated session instead of replaying the invitation token. Apply this only when that session is already authorized for the requested access; authentication alone does not establish membership or access rights.

Continue enforcing the normal membership and access checks, and handle a missing, expired, or unauthorized session through the normal invitation or sign-in path. This is a narrow browser-flow pattern for invitations exchanged once for longer-lived sessions; it does not bypass access checks or establish an empirical result.