Function serialize_subtree 

pub fn serialize_subtree(
    world: &World,
    root: EntityId,
) -> Result<Vec<u8>, SerializationError>

Encodes the subtree rooted at root (root + all descendants reached via the Children component) as a stand-alone bincode-encoded SceneRecipe. Exists to back the editor’s “Save as Prefab” flow: the resulting bytes round-trip through instantiate_subtree.

Hierarchy edges are emitted only for parent/child pairs whose both endpoints live inside the subtree, so a .kprefab file is fully self-contained. The first Spawn command is the prefab root.