WIP: force check layers to execute via CHECK_EPOCH build arg

script/cibuild

@@ -6,9 +6,14 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# A bare "docker build ." serves the check layers straight from the Docker
+# layer cache when the tree has not changed, so the build exits 0 without ever
+# running the checks. CHECK_EPOCH changes on every invocation and the
+# Dockerfile declares it above the checks in every stage that runs one, which
+# forces them to execute while leaving the dependency layers cached.
 main() {
     cd "$ROOT"
-    docker build .
+    docker build --build-arg CHECK_EPOCH="$(date +%s)" .
 }
 
 main "$@"