Bundles Ruby 4.0, Chromium (for snapshots), and SQLite so
sessions start with all dependencies pre-installed.

Assisted-by: Claude Opus 4.6 via pi

diff --git a/.ramekin/Dockerfile b/.ramekin/Dockerfile
new file mode 100644
index 0000000..f86b871
--- /dev/null
+++ b/.ramekin/Dockerfile
@@ -0,0 +1,29 @@
+FROM ruby:4.0-slim AS ruby
+
+FROM ramekin-agent
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    chromium \
+    libyaml-0-2 \
+    libsqlite3-dev \
+    sqlite3 \
+    && rm -rf /var/lib/apt/lists/*
+
+# Ruby 4.0 from the official image (Debian repos only have 3.3).
+COPY --from=ruby /usr/local/bin/ruby /usr/local/bin/
+COPY --from=ruby /usr/local/bin/bundle /usr/local/bin/
+COPY --from=ruby /usr/local/lib/libruby.so* /usr/local/lib/
+COPY --from=ruby /usr/local/lib/ruby/ /usr/local/lib/ruby/
+COPY --from=ruby /usr/local/include/ /usr/local/include/
+
+# For bootstrapping, so that we can use `rake` to create binstubs
+COPY --from=ruby /usr/local/bin/rake /usr/local/bin/
+RUN bundle config set --global bin /usr/local/bin
+
+# Install gems (including dev group for tests and snapshots).
+COPY Gemfile Gemfile.lock ./
+RUN bundle install
+
+WORKDIR /workspace
+
+ENTRYPOINT ["pi"]