Every plugin iframe loaded /plugin-sandbox, a force-dynamic Next page.
Each frame then fetched, parsed and hydrated Next's client router on top
of React and the runtime, and the server rendered the page once per
frame, one after another when a dozen plugins started together.
Sandboxed frames have opaque origins, so the browser's code cache never
helps, and they run on the host page's main thread: with 12 plugins
the frames took 2.5-3 s to come up after the app had loaded.
The sandbox routes now return a small HTML page with the UI kit's
stylesheet and the runtime as an ES module, both built ahead of time:
- `scripts/build-plugin-sandbox.mjs` bundles the runtime with esbuild
and compiles `plugin-kit.css` with the app's Tailwind setup into
`public/plugin-sandbox-assets/`, with a manifest. Named Tabler imports
are pointed at the icons' own files, so the full icon set stays in a
chunk that only loads for an icon name the kit doesn't ship.
- `npm run build`, `npm run dev`, the Dockerfile and the perf-guard
workflow run it before `next build`.
- `lib/plugin-sandbox/sandbox-document.ts` writes the page; proxy.ts
still sets the sandbox CSP and the script carries its nonce.
- The assets are served from public/ with CORS and immutable caching.
A frame on an idle page is ready in 255 ms instead of 362 ms, eleven at
once in 1.0 s instead of 2.1 s.
Paths the proxy skips (static files, `/_next`, `/api`) got no security
headers at all, so the not-found shell rendered for a missing
`/foo.html`, `/branding/x` or an unknown `/api` route could be framed
by any site. Skipped responses now carry `nosniff` and
`X-Frame-Options: DENY`, and non-API ones `frame-ancestors 'none'`;
API routes keep setting their own CSP.
Linus Rath