diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
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+# CI on the self-hosted GitLab, ported from .github/workflows/shellcheck.yml
+# when the GitHub account was suspended on 2026-09-20. The Actions file stays
+# in the tree as the reference.
+#
+# ludeeus/action-shellcheck has no GitLab equivalent, so this runs shellcheck
+# directly from its own digest-pinned image and reproduces the settings the
+# action was given: severity=warning, gcc format, every script in one run.
+
+stages: [lint]
+
+shellcheck:
+  stage: lint
+  # The -alpine variant, not koalaman/shellcheck:stable. That one is built
+  # FROM scratch with shellcheck as the entrypoint and no shell at all, so the
+  # runner cannot start a job script in it and the job dies before it runs
+  # ("OCI runtime create failed"). Clearing the entrypoint does not help: there
+  # is still no /bin/sh to clear it to.
+  image: koalaman/shellcheck-alpine:stable@sha256:c82fe42504fbc9fc68f15d36638e5ee2324ebb8b94e96a3c4e395bf361c49183 # stable
+  script:
+    - |
+      files=$(find . -name '*.sh' -not -path './.git/*' | sort)
+      [ -n "$files" ] || { echo "no shell scripts found"; exit 1; }
+      echo "$files" | tr '\n' ' '
+      shellcheck --severity=warning --format=gcc $files
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH