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+# syntax=docker/dockerfile:1
+#
+# garmin-otp/docs: documentation checks for `make docs`.
+#   * markdownlint-cli2 lints every Markdown file.
+#   * mermaid-cli renders every Mermaid diagram to SVG (build/docs/), which
+#     proves the diagrams parse; it drives a headless Chrome through Puppeteer.
+#
+# Reproducibility: the Node base image is pinned by digest, Debian packages come
+# from a dated snapshot, npm packages install from package-lock.json (resolved
+# from releases published before the cutoff date in the Makefile), and the
+# headless Chrome build is the one pinned by that Puppeteer version.
+
+ARG NODE_IMAGE=node@sha256:c3de60bf2f9dd0ac6370e6117950ff62d6e339527e7472301c9c78a017978392
+FROM ${NODE_IMAGE}
+
+# Dated snapshot of the Debian archive (https://snapshot.debian.org).
+ARG DEBIAN_SNAPSHOT=20261001T000000Z
+
+LABEL project=garmin-otp \
+      org.opencontainers.image.title="garmin-otp/docs" \
+      org.opencontainers.image.description="Markdown lint and Mermaid rendering for the project docs"
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    LANG=C.UTF-8 \
+    LC_ALL=C.UTF-8
+
+# CA certificates first, so apt can use the HTTPS snapshot mirror. They come
+# from the image's default (signed) Debian sources.
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends ca-certificates \
+ && rm -rf /var/lib/apt/lists/*
+
+# Shared libraries headless Chrome needs, plus fonts for diagram labels.
+# Snapshot Release files carry expired Valid-Until dates by design, so that
+# check is switched off; signatures are still verified.
+RUN rm -f /etc/apt/sources.list.d/debian.sources \
+ && printf '%s\n' \
+      "deb https://snapshot.debian.org/archive/debian/${DEBIAN_SNAPSHOT} bookworm main" \
+      "deb https://snapshot.debian.org/archive/debian/${DEBIAN_SNAPSHOT} bookworm-updates main" \
+      "deb https://snapshot.debian.org/archive/debian-security/${DEBIAN_SNAPSHOT} bookworm-security main" \
+      > /etc/apt/sources.list \
+ && echo 'Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/99snapshot \
+ && apt-get update \
+ && apt-get install -y --no-install-recommends \
+      libnss3 libnspr4 libatk1.0-0 libatk-bridge2.0-0 libcups2 libdrm2 libdbus-1-3 \
+      libxkbcommon0 libxcomposite1 libxdamage1 libxfixes3 libxrandr2 libxshmfence1 \
+      libgbm1 libasound2 libpango-1.0-0 libcairo2 libx11-xcb1 libexpat1 \
+      fonts-dejavu-core fonts-liberation \
+      unzip \
+ && rm -rf /var/lib/apt/lists/*
+
+# npm packages from the lock file. Install scripts are disabled; the one
+# download a script would do (Puppeteer's browser) is done explicitly instead,
+# so it lands in a known folder inside the image.
+WORKDIR /opt/docs-tools
+ENV PUPPETEER_CACHE_DIR=/opt/docs-tools/puppeteer-cache
+COPY docs/package.json docs/package-lock.json docs/puppeteer.json ./
+RUN npm ci --ignore-scripts --no-audit --no-fund \
+ && npx --no-install puppeteer browsers install chrome-headless-shell \
+ && chmod -R a+rX /opt/docs-tools
+
+ENV PATH=/opt/docs-tools/node_modules/.bin:${PATH} \
+    HOME=/tmp
+WORKDIR /work