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+name: Mirror distroless images
+
+# Keeps https://img.dieschoenewolke.de in step with gcr.io/distroless.
+#
+# The copying is done by zot's sync extension on the VPS, not by this job: the
+# registry diffs digests itself, pulls only what changed, and can do so while
+# the home Forgejo instance (and this runner) is down. This workflow is the
+# auditor — it compares upstream and mirror digests, pull-verifies anything new,
+# and only then writes a `synced-<repo>-<tag>-<digest12>` marker tag.
+#
+# That is the same "marker last" discipline as the Pureblog release pipeline:
+# a marker exists only for a ref that was proven pullable by digest. A run that
+# dies before the push leaves no marker, so the next run retries.
+#
+# gcr.io load: one anonymous token request per repo plus one manifest request
+# per ref = 8 requests per run, every 6 hours. No per-request storm, no docker
+# login, nothing that could hit an anonymous rate limit.
+
+on:
+  schedule:
+    - cron: "17 */6 * * *"
+  workflow_dispatch:
+    inputs:
+      verify_all:
+        description: "Pull-verify every ref, not just new digests (1/0)"
+        required: false
+        default: "0"
+        type: string
+
+concurrency:
+  group: distroless-mirror-sync
+  # Never cancel a run half way: a cancelled run could leave a tag pushed
+  # without the verification it claims. Runs are minutes apart anyway.
+  cancel-in-progress: false
+
+jobs:
+  verify:
+    runs-on: docker-cli
+    timeout-minutes: 30
+    container:
+      image: docker:29-cli
+    steps:
+      - name: Install workflow tools
+        run: apk add --no-cache bash curl git jq
+
+      - name: Check out the marker tags
+        uses: https://github.com/actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Compare upstream and mirror, verify, mark
+        env:
+          # docker:cli keeps the CLI in /usr/local/bin; the runner's DOCKER_HOST
+          # points at the daemon, so the pull goes over the public hostname and
+          # the real TLS/edge path.
+          VERIFY_PULL: ${{ inputs.verify_all == '1' && 'always' || 'new' }}
+          MARKERS_FILE: ${{ runner.temp }}/mirror-markers
+        run: ./scripts/verify-mirror.sh
+
+      - name: Publish marker tags
+        run: |
+          set -eu
+          file="${MARKERS_FILE:-$RUNNER_TEMP/mirror-markers}"
+          [ -s "$file" ] || { echo "no new markers"; exit 0; }
+          while read -r marker; do
+            [ -n "$marker" ] || continue
+            git push origin "refs/tags/$marker"
+            echo "marked $marker"
+          done <"$file"