refactor(M03): extract M2 mesh resource cache state

Work-Package: M03-RND-M2-MESH-RESOURCE-CACHE-001
Agent: sindo-main-codex
Tests: 35 headless renderer/coordinate contracts pass; checkpoint dry-run 7/7; documentation and coordination gates pass
Fidelity: preserves exact Mesh references, replacement semantics and final-shutdown lifetime; no visual parity claim

src/render/m2/m2_mesh_resource_cache_state.gd

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+class_name M2MeshResourceCacheState
+extends RefCounted
+
+## Owns normalized-path references to prepared static M2 Mesh resources.
+## The caller owns loading, preparation, missing-state and materialization.
+
+var _mesh_by_normalized_path: Dictionary = {}
+
+
+## Stores one prepared Mesh for a non-empty normalized M2 path. A later store
+## for the same path replaces the retained reference.
+func store_mesh(normalized_relative_path: String, mesh: Mesh) -> bool:
+	if normalized_relative_path.is_empty() or mesh == null:
+		return false
+	_mesh_by_normalized_path[normalized_relative_path] = mesh
+	return true
+
+
+## Returns whether one normalized path currently has a retained Mesh.
+func has_mesh(normalized_relative_path: String) -> bool:
+	return (
+		not normalized_relative_path.is_empty()
+		and _mesh_by_normalized_path.has(normalized_relative_path)
+	)
+
+
+## Returns the exact retained Mesh reference, or null for empty/unknown paths.
+func find_mesh(normalized_relative_path: String) -> Mesh:
+	if not has_mesh(normalized_relative_path):
+		return null
+	return _mesh_by_normalized_path[normalized_relative_path] as Mesh
+
+
+## Returns the number of retained static M2 Mesh resources.
+func mesh_count() -> int:
+	return _mesh_by_normalized_path.size()
+
+
+## Returns a detached insertion-order list of cached normalized paths.
+func normalized_paths_snapshot() -> Array[String]:
+	var normalized_paths: Array[String] = []
+	for normalized_path_variant in _mesh_by_normalized_path.keys():
+		normalized_paths.append(String(normalized_path_variant))
+	return normalized_paths
+
+
+## Releases all retained Mesh references. The loader calls this only after
+## asynchronous work has completed during final scene shutdown.
+func clear() -> void:
+	_mesh_by_normalized_path.clear()

src/render/m2/m2_mesh_resource_cache_state.gd.uid

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+uid://dhkyjcrdblgkd