Function try_export_glb_from_meshes 

pub fn try_export_glb_from_meshes(
    positions: &[f32],
    normals: &[f32],
    indices: &[u32],
    vertex_counts: &[u32],
    index_counts: &[u32],
    colors: &[f32],
    origins: &[f64],
    express_ids: &[u32],
    include_metadata: bool,
    lit: bool,
    emissive: bool,
) -> Result<(Vec<u8>, GltfStats), ExportError>

Fail-closed export_glb_from_meshes: validates the per-mesh vertex_counts / index_counts (and normals) against the flattened buffers, and the index VALUES against the vertex counts, BEFORE assembling. Returns ExportError::MalformedMeshInput when a declared vertex/index count runs past the end of positions / indices, an index_counts entry is missing, normals is empty or too short to cover every emitted vertex, or an index names a vertex its own mesh does not have — instead of silently dropping the un-backed meshes (which the infallible variant does — a valid GLB missing part of the model, reported as success) or copying the out-of-range index straight into the BIN chunk. Prefer this at any boundary where the counts and buffers come from separate sources (the wasm FFI).