Proposed Canon
A fugitive is a prisoner who has managed to escape. They take their turn at the same time as their captor. They get to move before any other unit, as if they were the first to be given orders by the side. Since no one is paying their upkeep and even fugitive commanders do not get to have a purse like a barbarian, it is critical that the fugitive manages to forage enough food for a meal. If the fugitive fails to keep up with his/her upkeep, their move will drop to zero, chains will reappear, their captor will know their precise location, and the fugitive becomes a captive again, reliant on the capturing side to pay their upkeep.
Fugitive status ends when the unit in question manages to reach another unit on their side or claims a city.