Unfortunately, I think the appearance of long-term maintaining of an open source project would be just another gameable metric, especially with delegation to an AI slave, to make it almost zero cost.
Helicopter parents and then young adults are already long-term gaming metrics, before they start high school, just to get into college, and it seems that the same kinds of thinking persist through first job and rest of career.
Being seen as a long-term maintainer of an open source project is now trivial, compared to some of the other things people already do.
Offhand, ideas:
1. Use criteria the metrics-gamers won't think of, and don't tell them what it is. (Why this might work: the metrics-gaming mindset might blind people to thinking outside that mindset. Why this might not work: you need someone not blinded to apply the criteria.)
2. Do things that are unattractive to the metrics-gamers, but attractive to people who aren't. (Though you might still get overwhelmed by near-zero-cost AI spamming applications anyway.)
3. Accept that too many current workers were brought up with metrics-gaming mindset, and the others are too hard to find in the noise, and select and align metrics-gamers in game-theoretic ways. (Extreme example: you pay minimum wage, and there are no promotions nor titles nor performance evaluation metrics not anything except success of the company, but everyone gets real equity that's worth zero unless the team together delivers and wins, in which case everyone gets equally wealthy. The trick would be convincing the dumber metrics-gamers that they can't just nod and game this, and if they don't play like a team member for the team to win, they will be voted off the island and get zero, and possibly left in a ditch.)