Function append_mesh 

pub fn append_mesh(
    ctx: &mut PipelineContext<'_>,
    id: AssetId,
    payload: Vec<u8>,
) -> MeshHandle

Record payload as id’s geometry and return the handle it lands on.

A mesh installed here trails the build’s four compiled blocks (the build assigns Mesh, ProceduralMesh, VoxelChunk, and File blocks in that order), so it moves no handle a compiled world baked into a Prop.