level_clear.gd gained a next_level_scene export: empty reloads the current level, otherwise it changes to the given scene. Level 1 now points at res://scenes/level_2.tscn. level_2.tscn is an empty but complete level: background, three TileMapLayers wired to the same TileSet, player, HUD, death screen and level-clear screen, plus the empty prefab containers. Its hidden_passages script explicitly sets hidden_cells = [] so level 1's passage cells are not carved here.
The three diamonds and both doors were painted as tiles in TerrainBase, which cannot act as pickups or triggers. Replaced them with real prefabs that reuse the same atlas tiles (diamond = (7,3), doors = (10,6) and (11,5)) and erase their placeholder tile on ready. Collecting all three diamonds unlocks the door; touching it fades to black, pauses the tree and shows the level-clear screen with a next-level button (currently reloads the level, as there is only one). HUD now shows the diamond count.
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