Copyright header

sparse_strips/vello_bench/src/flatten.rs

diff --git a/sparse_strips/vello_bench/src/flatten.rs b/sparse_strips/vello_bench/src/flatten.rs
index 044a4ef..8a477d2 100644
--- a/sparse_strips/vello_bench/src/flatten.rs
+++ b/sparse_strips/vello_bench/src/flatten.rs
@@ -1,3 +1,6 @@
+// Copyright 2025 the Vello Authors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use crate::data::get_data_items;
 use criterion::Criterion;
 use vello_common::flatten;