Nomad changes

scripts/publish/check-docker-tag.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+tag="${DOCKER_TAG:?DOCKER_TAG not set}"
+label="${SUMMARY_LABEL:-image}"
+
+exists=false
+if docker manifest inspect "$tag" >/dev/null 2>&1; then
+  exists=true
+fi
+
+echo "exists=$exists" >>"${GITHUB_OUTPUT:?GITHUB_OUTPUT not set}"
+
+if [ "$exists" = "true" ] && [ -n "${GITHUB_STEP_SUMMARY:-}" ]; then
+  echo "Docker tag $tag already exists; ${label} publish will be skipped." >>"$GITHUB_STEP_SUMMARY"
+fi