fix: center ground under chunks and align player spawn with chunk grid

scripts/smoke_test_world_chunk_alignment.gd

@@ -0,0 +1,109 @@
+extends SceneTree
+## Regression test for world chunk alignment and ground positioning.
+
+var _passed: int = 0
+var _failed: int = 0
+
+
+func _check(label: String, condition: bool) -> void:
+	if condition:
+		print("  PASS: %s" % label)
+		_passed += 1
+	else:
+		printerr("  FAIL: %s" % label)
+		_failed += 1
+
+
+func _init() -> void:
+	call_deferred("_run_tests")
+
+
+func _run_tests() -> void:
+	print("--- World Chunk & Ground Alignment Test ---")
+	await process_frame
+
+	var packed: PackedScene = load("res://scenes/game.tscn")
+	var result := change_scene_to_packed(packed)
+	if result != OK:
+		printerr("SMOKE: failed to change scene, error ", result)
+		quit(1)
+		return
+
+	await scene_changed
+	var game: Node3D = current_scene as Node3D
+	_check("game scene ready", game != null)
+
+	# Initially, ground is at default test level position (0, -0.5, 0)
+	var ground: StaticBody3D = game.get_node_or_null("Level/Ground") as StaticBody3D
+	_check("Ground initially exists", ground != null)
+	_check("Ground initially at (0, -0.5, 0)", ground.position.is_equal_approx(Vector3(0, -0.5, 0)))
+
+	# Create a ChunkScene for chunk (0, 0, 0) with corner objects
+	var chunk_scene := ChunkScene.new()
+	chunk_scene.coord = Vector3i(0, 0, 0)
+	chunk_scene.name = "chunk_0_0_0"
+	game.add_child(chunk_scene)
+
+	# Add lamp post at corner (0.5, 0.5) and corner (31.5, 31.5)
+	var obj_corner1 := WorldObject.new()
+	obj_corner1.id = "lamp1"
+	obj_corner1.type = "prop"
+	obj_corner1.position = Vector3(0.5, 0.5, 0.0)
+	obj_corner1.properties = {"catalog_id": "lamp_post_01"}
+	chunk_scene.add_object(obj_corner1)
+
+	var obj_corner2 := WorldObject.new()
+	obj_corner2.id = "lamp2"
+	obj_corner2.type = "prop"
+	obj_corner2.position = Vector3(31.5, 31.5, 0.0)
+	obj_corner2.properties = {"catalog_id": "lamp_post_01"}
+	chunk_scene.add_object(obj_corner2)
+
+	# Trigger _on_chunk_loaded
+	game.call("_on_chunk_loaded", Vector3i(0, 0, 0), chunk_scene)
+
+	# Verify Ground has moved to center of chunk: (16.0, -0.5, 16.0)
+	_check("Ground moved to chunk center (16, -0.5, 16)", ground.position.is_equal_approx(Vector3(16.0, -0.5, 16.0)))
+
+	var shape_node := ground.find_child("CollisionShape3D", true, false) as CollisionShape3D
+	_check("Ground CollisionShape3D size >= 40x40", shape_node != null and (shape_node.shape as BoxShape3D).size.x >= 40.0 and (shape_node.shape as BoxShape3D).size.z >= 40.0)
+
+	var mesh_node := ground.find_child("MeshInstance3D", true, false) as MeshInstance3D
+	_check("Ground MeshInstance3D size >= 40x40", mesh_node != null and (mesh_node.mesh as BoxMesh).size.x >= 40.0 and (mesh_node.mesh as BoxMesh).size.z >= 40.0)
+
+	# Verify corners are inside ground bounds
+	var half_x: float = (shape_node.shape as BoxShape3D).size.x * 0.5
+	var half_z: float = (shape_node.shape as BoxShape3D).size.z * 0.5
+	var min_gx: float = ground.position.x - half_x
+	var max_gx: float = ground.position.x + half_x
+	var min_gz: float = ground.position.z - half_z
+	var max_gz: float = ground.position.z + half_z
+
+	_check("Corner (0.5, 0.5) is on ground", 0.5 >= min_gx and 0.5 <= max_gx and 0.5 >= min_gz and 0.5 <= max_gz)
+	_check("Corner (31.5, 31.5) is on ground", 31.5 >= min_gx and 31.5 <= max_gx and 31.5 >= min_gz and 31.5 <= max_gz)
+
+	# Verify PlayerSpawn defaulted to chunk center (16, 1.5, 16)
+	var spawn_marker := game.get_node_or_null("Level/PlayerSpawn") as Node3D
+	_check("PlayerSpawn marker is at (16, 1.5, 16)", spawn_marker != null and spawn_marker.global_position.is_equal_approx(Vector3(16.0, 1.5, 16.0)))
+
+	# Now test placed spawn_point object
+	var chunk_scene2 := ChunkScene.new()
+	chunk_scene2.coord = Vector3i(0, 0, 0)
+	chunk_scene2.name = "chunk_with_spawn"
+	game.add_child(chunk_scene2)
+
+	var spawn_obj := WorldObject.new()
+	spawn_obj.id = "spawn1"
+	spawn_obj.type = "spawn_point"
+	spawn_obj.position = Vector3(8.5, 12.5, 0.0)
+	spawn_obj.properties = {"catalog_id": "spawn_point"}
+	chunk_scene2.add_object(spawn_obj)
+
+	game.call("_on_chunk_loaded", Vector3i(0, 0, 0), chunk_scene2)
+	_check("PlayerSpawn moved to placed spawn_point at (8.5, 1.5, 12.5)", spawn_marker != null and spawn_marker.global_position.is_equal_approx(Vector3(8.5, 1.5, 12.5)))
+
+	print("\n=== SMOKE RESULT: %d/%d passed ===" % [_passed, _passed + _failed])
+	if _failed > 0:
+		quit(1)
+	else:
+		quit(0)