diff --git a/tools/build-remote.sh b/tools/build-remote.sh
index f63618bf3..920939884 100755
--- a/tools/build-remote.sh
+++ b/tools/build-remote.sh
@@ -19,6 +19,8 @@
 #                                                                            recompiled between the builds (mimalloc's __DATE__), with
 #                                                                            and without SOURCE_DATE_EPOCH. Takes 2 to 6 min on the box.
 #
+# Sources: HEAD through the bare mirror, uncommitted changes by rsync --checksum, every written file re-stamped with touch in
+# lib.sh's bs_overlay_dir (the copied-sources rule; tools/ci/copied-sources-check.sh reads this file for that word).
 # Reproducible: every command runs with SOURCE_DATE_EPOCH = the commit's author time and TZ=UTC, into ONE fixed target directory per
 # target (lib.sh bs_repro_env; main's rule of 6 October 2026 from the 0.3.14 repro: prost embeds OUT_DIR, mimalloc embeds the date).
 #