Mushroom groves: unclaimable moss where giant mushrooms grow slowly and glow when ready to fell

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

src/game.rs

@@ -2609,7 +2609,12 @@ impl Game {
     pub fn dig_out(&mut self, i: usize) {
         self.torches.retain(|t| t.wall != i);
         let t = &mut self.map.t[i];
-        t.kind = Kind::Floor;
+        // a grove's mushroom leaves its moss behind
+        let grove = t.kind == Kind::Mushroom && t.res & MUSH_GROVE != 0;
+        t.kind = if grove { Kind::Grove } else { Kind::Floor };
+        if grove {
+            t.res = 0;
+        }
         t.owner = Owner::None;
         t.marked = false;
         t.reinforced = false;