refactor(M03): extract M2 mesh resource traversal

Work-Package: M03-RND-M2-MESH-RESOURCE-EXTRACTOR-001
Agent: sindo-main-codex
Tests: 36 headless renderer/coordinate contracts pass; checkpoint dry-run 7/7; documentation and coordination gates pass
Fidelity: preserves first-Mesh preorder and temporary PackedScene cleanup; no visual parity claim

src/render/m2/m2_mesh_resource_extractor.gd

@@ -0,0 +1,34 @@
+class_name M2MeshResourceExtractor
+extends RefCounted
+
+## Selects the first Mesh from loaded M2 Resources or existing Node subtrees.
+## The caller owns ResourceLoader I/O, cache adoption and material preparation.
+
+
+## Returns the direct Mesh Resource or the first Mesh in a temporary PackedScene
+## instance. The temporary instance is freed before this method returns.
+func extract_first_mesh(resource: Resource) -> Mesh:
+	if resource is Mesh:
+		return resource as Mesh
+	if not (resource is PackedScene):
+		return null
+	var temporary_root := (resource as PackedScene).instantiate()
+	if temporary_root == null:
+		return null
+	var mesh := find_first_mesh_in_subtree(temporary_root)
+	temporary_root.free()
+	return mesh
+
+
+## Returns the first MeshInstance3D Mesh in depth-first preorder. The subtree
+## and Mesh ownership remain unchanged.
+func find_first_mesh_in_subtree(root: Node) -> Mesh:
+	if root == null:
+		return null
+	if root is MeshInstance3D:
+		return (root as MeshInstance3D).mesh
+	for child in root.get_children():
+		var mesh := find_first_mesh_in_subtree(child)
+		if mesh != null:
+			return mesh
+	return null

src/render/m2/m2_mesh_resource_extractor.gd.uid

@@ -0,0 +1 @@
+uid://dea4gekrxshjf