Summary

Stacks on top of #2. Every component and chart docs page was loading @babel/standalone@7.29.0/babel.min.js (~600 KB) from unpkg purely to transform JSX strings that are already known at build time. This PR pre-transforms them with esbuild during build:site and drops the in-browser Babel pass entirely.

What changed

• New compileDemo(jsxCode) in scripts/build-docs.mjs uses esbuild.transformSync (already a dev-dep, no new packages) with the classic JSX runtime — jsxFactory: "React.createElement", jsxFragment: "React.Fragment". Both names are bound in the runner factory via var { React, …, createRoot } = R, so the transformed JS evaluates as-is.
• renderComponentPage now passes the compiled JS string to runExample / runChartExample. The displayed code panel and copy-button still receive the original JSX via DEMO_CODES — same UX, same source-of-truth.
• renderRunner() dropped the Babel.transform pass and the if (!global.Babel) guard. The per-page readiness gate switched from window.RCS && window.Babel to just the bundle global the page needs (window.RCS or window.RCSCharts).
• The <script src="https://unpkg.com/@babel/standalone@7.29.0/babel.min.js"> tag was removed from the component-page tail.

What this does NOT touch

• /docs/playground/ still loads Babel-standalone — it has to, since it transforms whatever JSX the user types.
• ui_kits/{app,marketing,docs}/index.html sample apps each ship their own Babel-standalone for their internal renders. Self-contained demo apps; out of scope.
• The cytoscape peer dep contains an internal "@babel/helpers - typeof" comment string inside rcs-charts.iife.js. That's a substring match, not a runtime Babel load.

Verification

$ pnpm typecheck                # clean
$ pnpm test -- tests/unit/Sparkline.test.tsx  # 4/4
$ pnpm run build:site
  rcs.iife.js         236.5 KB  (unchanged)
  rcs-charts.iife.js  793.9 KB  (unchanged)
  rcs-charts.iife.css   1.6 KB  (unchanged)
  58 component pages, foundations, playground, etc.

Spot checks on the generated _site/:

• /docs/Button/index.html → contains runExample("/* @__PURE__ */ React.createElement(Button, null)", "demo-render-0"). No <script src="…@babel/standalone…">.
• /docs/Chart/index.html → contains runChartExample("/* @__PURE__ */ React.createElement(\n Chart,\n {\n timestamps: …", …). No <script src="…@babel/standalone…">.
• runner.js → 4.2 KB → 2.7 KB.
• grep -rln '@babel/standalone\|babel\.min\.js' _site/ → returns only the playground and the 3 ui_kits demo apps (expected).

Per-page transfer impact

Each of the 58 component / chart docs pages no longer fetches ~600 KB of Babel-standalone on first load and no longer runs an in-browser JSX compile pass. The compiled React.createElement(...) strings inline into each page tail — Button page grew from ~17 KB to ~20 KB, but the net is -580 KB per load.

Test plan

• pnpm typecheck
• Unit tests touching chart code still pass
• pnpm run build:site clean
• Generated HTML spot-checks (Button, Chart, runner.js)
• Pages workflow green on push (CI)
• E2E workflow green on push (CI) — Playwright will exercise the pre-transformed demo pipeline
• Manual: open pnpm run serve:site, confirm Button + Chart + Sparkline pages render the live demo and the toggle still shows JSX

Note on PR base

This PR targets feat/react-only-docs (the base PR #2), not main. Once #2 lands, GitHub will retarget this to main automatically.

🤖 Generated with Claude Code