refactor(M03): extract WMO render build queue

src/render/wmo/wmo_render_build_job.gd

@@ -0,0 +1,59 @@
+class_name WmoRenderBuildJob
+extends RefCounted
+
+## Holds one lightweight-WMO build cursor and strong engine-object references.
+## Releasing this record never frees the referenced Node or Resource.
+
+var _placement_key: String
+var _root: Node3D
+var _render_resource: Resource
+var _mesh_index: int = 0
+var _multimesh_index: int = 0
+
+
+func _init(placement_key: String, root: Node3D, render_resource: Resource) -> void:
+	_placement_key = placement_key
+	_root = root
+	_render_resource = render_resource
+
+
+## Returns the immutable placement identity used by the queue.
+func placement_key() -> String:
+	return _placement_key
+
+
+## Returns the strongly referenced scene root without transferring ownership.
+func root() -> Node3D:
+	return _root
+
+
+## Returns the strongly referenced render resource without transferring ownership.
+func render_resource() -> Resource:
+	return _render_resource
+
+
+## Returns the current mesh-group cursor.
+func mesh_index() -> int:
+	return _mesh_index
+
+
+## Returns the current doodad MultiMesh-group cursor.
+func multimesh_index() -> int:
+	return _multimesh_index
+
+
+## Atomically adopts both cursor values returned by the pure step planner.
+func adopt_cursors(next_mesh_index: int, next_multimesh_index: int) -> void:
+	_mesh_index = next_mesh_index
+	_multimesh_index = next_multimesh_index
+
+
+## Returns detached scalar state and never exposes engine-object references.
+func diagnostic_snapshot() -> Dictionary:
+	return {
+		"placement_key": _placement_key,
+		"mesh_index": _mesh_index,
+		"multimesh_index": _multimesh_index,
+		"has_root": _root != null,
+		"has_render_resource": _render_resource != null,
+	}