Final missions above ground (M30, co-op M20), surface option for versus matches, docs

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

src/main.rs

@@ -349,7 +349,7 @@ fn account_action(a: MenuAction, cloud: &mut Cloud, menu: &mut Menu, app: &mut A
             }
         }
         MenuAction::MatchJoin(code) => app.client.join(&code),
-        MenuAction::MatchCreate => app.client.create(&[0, 2, 3, 4], app.settings.map_w, app.settings.map_h, app.settings.difficulty),
+        MenuAction::MatchCreate => app.client.create_land(&[0, 2, 3, 4], app.settings.map_w, app.settings.map_h, app.settings.difficulty, app.settings.surface),
         MenuAction::MatchCoopCreate(mission) => {
             let all = campaign::missions();
             if let Some(d) = all.get(mission) {
@@ -692,7 +692,7 @@ impl App {
         let next = run_seed.is_some();
         let seed = run_seed.unwrap_or_else(|| next_seed(self.seed));
         let editor = doc.is_some();
-        let info = StartInfo { seed, map_w, map_h, difficulty: self.settings.difficulty, sides: vec![0, 2], local_side: Some(0), mission: Some(mission), ai: vec![2], doc, editor, teams: Vec::new(), next, carry };
+        let info = StartInfo { seed, map_w, map_h, difficulty: self.settings.difficulty, sides: vec![0, 2], local_side: Some(0), mission: Some(mission), ai: vec![2], doc, editor, teams: Vec::new(), next, carry, surface: false };
         if !self.start_match_game(info) {
             return false;
         }
@@ -772,6 +772,10 @@ impl App {
         if !self.game.start_match(&info.sides, local) {
             return false;
         }
+        if info.surface {
+            // the same land on every client: built from the shared seed
+            self.game.add_surface(info.seed, 0.5, 2 + (info.map_h / 64) as u32);
+        }
         self.game.coop = false;
         self.game.set_teams(&info.teams);
         self.game.ai_difficulty = info.difficulty;