Assisted-by: Claude

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+# Ramekin image for pro-tacts (Ruby 4 CardDAV server).
+#
+# FROM ramekin-agent to keep the pi harness. Switch to ramekin-base for a
+# leaner image without the agent.
+#
+# Ruby 4 is not in trixie's apt (it ships 3.x), so Ruby is built from source.
+# Adjust RUBY_VERSION if the released patch differs from the default.
+
+FROM ramekin-agent
+
+ARG RUBY_VERSION=4.0.0
+ENV RUBY_VERSION=${RUBY_VERSION}
+
+# Toolchain and headers for building Ruby and for any native gem that lacks a
+# precompiled binary (nokogiri and puma usually ship one, but keep these).
+RUN apt-get update && apt-get install -y --no-install-recommends \
+      build-essential autoconf bison \
+      libssl-dev libyaml-dev libreadline-dev zlib1g-dev libffi-dev \
+      ca-certificates wget \
+ && rm -rf /var/lib/apt/lists/*
+
+RUN wget -q "https://cache.ruby-lang.org/pub/ruby/${RUBY_VERSION%.*}/ruby-${RUBY_VERSION}.tar.gz" \
+ && tar -xzf "ruby-${RUBY_VERSION}.tar.gz" \
+ && cd "ruby-${RUBY_VERSION}" \
+ && ./configure --disable-install-doc \
+ && make -j"$(nproc)" \
+ && make install \
+ && cd / && rm -rf "ruby-${RUBY_VERSION}" "ruby-${RUBY_VERSION}.tar.gz"
+
+# Match the bundler pinned in Gemfile.lock (BUNDLED WITH).
+RUN gem install bundler -v 4.0.3
+
+# Install project gems at build time so bundle/rake/puma are ready each session.
+# Build context is expected to be the project root. The lockfile is darwin-only,
+# so add the linux platforms before resolving or the native gems won't install.
+COPY Gemfile Gemfile.lock /tmp/bundle/
+RUN cd /tmp/bundle \
+ && bundle lock --add-platform aarch64-linux \
+ && bundle lock --add-platform x86_64-linux \
+ && bundle install --jobs 4 \
+ && rm -rf /tmp/bundle