A tracking link is only useful if it doesn't outlive its purpose. That's why journey.delivery doesn't rely on a link alone — every journey has its own closed list of invited viewers.
To watch a trip, a viewer needs three things: the driver's public tracking ID, the trip's 6-digit PIN, and their own email address — which must match an invitation sent for that specific journey. Being invited to one trip never carries over to another. An old PIN, a forwarded link, or a lucky guess isn't enough on its own.
It's a small design decision with a real effect: the people watching a delivery are always exactly the people the driver chose, for exactly the trip they were invited to.