Embed interactive playgrounds in the web thread

[time-attack]

Summary

• When someone asks to see or play with a mechanism, the agent can store a self-contained HTML miniapp and put [[miniapp: url | title]] in the reply so the web UI renders a Play / Code card in the thread.
• Slack strips the marker and does not teach or render playground buttons. Playgrounds stay a web surface.
• Inline scripts are parsed before store; empty, networked, or broken pages are rejected. The host injects light/dark tokens and a first-paint probe so the card does not hang.

Test plan

• node --experimental-test-module-mocks --test test/miniapp.test.ts test/skill-conformance.test.ts test/pi-tools.test.ts test/route-auth-conformance.test.ts test/dev-cli-lib.test.ts
• npm test -- test/miniapp.test.ts test/miniapp-proxy.test.ts in plugins/web-ui
• node --test test/router.test.ts in plugins/portal
• In a local web UI thread, ask to play with a mechanism (e.g. Riemann sums / drag the rectangles) and confirm a playground card appears with Play and highlighted Code.
• Confirm ordinary Q&A does not auto-build a playground.
• Confirm a Slack reply that includes a miniapp marker shows only the stripped text (no buttons, no raw [[miniapp:…]]).
• Open /m/:id/:key and /m/:id/:key?view=source through portal and web-ui; iframe should load (no X-Frame-Options), source should be raw HTML.

Made with Cursor

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[time-attack]

Live web-thread take: new chat, asked to explain integrals and drag the rectangles. The playground card paints in the thread; then the slider, left/mid/right sampling, and the chart are driven live.

explain-integrals.mp4