Twin-server project profile

• Stack: React on Rails monorepo, Pro dummy Rails app at react_on_rails_pro/spec/dummy, SQLite test database, RSC node renderer.
• Runtime versions: Ruby 3.3.7, Node 22.12.0, pnpm 10.33.4.
• Server processes: Rails on container port 3000; node renderer on container port 3800.
• Runtime env: REACT_RENDERER_URL=http://localhost:3800 is set in Docker ENV and repeated literally in the Rails Procfile commands so host shell expansion cannot override it; the fixed dummy SECRET_KEY_BASE is passed by the Procfile when Rails starts instead of being part of image ENV.
• Backing services: SQLite only, prepared during image build with SECRET_KEY_BASE_DUMMY=1 RAILS_ENV=test bundle exec rails db:prepare.
• Build steps baked into image: root bundle install, root pnpm install --frozen-lockfile, root pnpm run build, dummy pack generation, dummy pnpm run build:test, dummy test DB prepare.
• RSC route note: RSCPostsPageOverHTTP fetches http://localhost:3000/api/posts; this works inside each twin-server container because Rails binds to container-local port 3000.