refactor(M03): extract terrain chunk LOD planner

src/render/terrain/terrain_chunk_lod_planner.gd

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+class_name TerrainChunkLodPlanner
+extends RefCounted
+
+## Pure linear desired-state planner for parsed ADT chunk records.
+
+const POLICY_SCRIPT := preload("res://src/render/terrain/terrain_chunk_lod_policy.gd")
+const GODOT_WORLD_POSITION_SCRIPT := preload("res://src/domain/coordinates/godot_world_position.gd")
+
+
+## Maps source chunk indices to LOD 0/1/2 using horizontal distance from the
+## typed focus to each chunk center. Empty/out-of-range chunks remain absent.
+func plan(
+		chunks: Array,
+		focus_position: RefCounted,
+		policy: RefCounted
+) -> Dictionary:
+	if (
+		focus_position == null
+		or focus_position.get_script() != GODOT_WORLD_POSITION_SCRIPT
+		or policy == null
+		or policy.get_script() != POLICY_SCRIPT
+		or not bool(policy.get("is_enabled"))
+	):
+		return {}
+
+	var chunk_size_units := float(policy.get("chunk_size_units"))
+	var lod0_radius_squared := (float(policy.get("lod0_radius_chunks")) * chunk_size_units) ** 2
+	var lod1_radius_squared := (float(policy.get("lod1_radius_chunks")) * chunk_size_units) ** 2
+	var lod2_radius_squared := (float(policy.get("lod2_radius_chunks")) * chunk_size_units) ** 2
+	var focus_x_units := float(focus_position.get("x_units"))
+	var focus_z_units := float(focus_position.get("z_units"))
+	var desired_lods: Dictionary = {}
+
+	for chunk_id in range(chunks.size()):
+		var chunk: Dictionary = chunks[chunk_id]
+		if chunk.is_empty():
+			continue
+		var origin: Vector3 = chunk.get("origin", Vector3.ZERO)
+		var center_x_units := origin.x + chunk_size_units * 0.5
+		var center_z_units := origin.z + chunk_size_units * 0.5
+		var delta_x_units := center_x_units - focus_x_units
+		var delta_z_units := center_z_units - focus_z_units
+		var distance_squared_units := (
+			delta_x_units * delta_x_units + delta_z_units * delta_z_units
+		)
+		if distance_squared_units <= lod0_radius_squared:
+			desired_lods[chunk_id] = 0
+		elif distance_squared_units <= lod1_radius_squared:
+			desired_lods[chunk_id] = 1
+		elif distance_squared_units <= lod2_radius_squared:
+			desired_lods[chunk_id] = 2
+
+	return desired_lods

src/render/terrain/terrain_chunk_lod_planner.gd.uid

@@ -0,0 +1 @@
+uid://x8simqkfctqw

src/render/terrain/terrain_chunk_lod_policy.gd

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+class_name TerrainChunkLodPolicy
+extends RefCounted
+
+## Immutable snapshot of the streamer's chunk-terrain LOD configuration.
+
+var is_enabled: bool:
+	get:
+		return _is_enabled
+
+var lod0_radius_chunks: int:
+	get:
+		return _lod0_radius_chunks
+
+var lod1_radius_chunks: int:
+	get:
+		return _lod1_radius_chunks
+
+var lod2_radius_chunks: int:
+	get:
+		return _lod2_radius_chunks
+
+var chunk_size_units: float:
+	get:
+		return _chunk_size_units
+
+var _is_enabled: bool
+var _lod0_radius_chunks: int
+var _lod1_radius_chunks: int
+var _lod2_radius_chunks: int
+var _chunk_size_units: float
+
+
+## Captures one renderer configuration snapshot for a deterministic plan.
+func _init(
+		is_enabled_value: bool,
+		lod0_radius_chunks_value: int,
+		lod1_radius_chunks_value: int,
+		lod2_radius_chunks_value: int,
+		chunk_size_units_value: float
+) -> void:
+	_is_enabled = is_enabled_value
+	_lod0_radius_chunks = lod0_radius_chunks_value
+	_lod1_radius_chunks = lod1_radius_chunks_value
+	_lod2_radius_chunks = lod2_radius_chunks_value
+	_chunk_size_units = chunk_size_units_value

src/render/terrain/terrain_chunk_lod_policy.gd.uid

@@ -0,0 +1 @@
+uid://dmwi83dp52pa8