Real AI masters: rivals, AI seats and the co-op partner play by the player's rules (imps dig, mine and claim, rooms, towers, tunnels and the attack flag); other masters are saved; portals belong to whoever claims them

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/campaign.rs

@@ -663,6 +663,8 @@ fn remove_rivals(g: &mut Game) {
         return;
     }
     g.rivals.clear();
+    // their masters go too (the seats belong to the players)
+    g.masters.retain(|m| !sides.contains(&m.side));
     g.ents.retain(|e| e.hero || !sides.contains(&e.side));
     let owners: Vec<Owner> = sides.iter().map(|&s| Owner::of_side(s)).collect();
     for t in g.map.t.iter_mut() {