improve position fixing

src/game.js

@@ -34,6 +34,10 @@ export default class Game {
     this.#terrains.push(terrain)
   }
 
+  remove_terrain(terrain) {
+    this.#terrains = this.#terrains.filter((t) => t.id != terrain.id)
+  }
+
   state() {
     return {
       ...this,