Sketch detail pages: OpenProcessing embeds stuck in loading state, never render

Most appropriate sections of the p5.js website?

Community (Sketches, Libraries, Events)

What is your operating system?

None

Web browser and version

No response

Actual Behavior

On all sketch detail pages (/sketches/{id}), the embed area displays a loading
spinner indefinitely. The sketch content never renders and no error message is shown.

Tested on:

• https://p5js.org/sketches/2690038/ ("Feelings make us human")
• https://p5js.org/sketches/2484739/ ("All you need is infinite love!")
• https://p5js.org/sketches/2689119/ ("Boiling Point")

All three reproduce the same failure consistently.

Expected Behavior

The embedded sketch should render in the embed area, or a graceful fallback
should be shown if the embed fails to load.

Steps to reproduce

1. Open any sketch detail page e.g. https://p5js.org/sketches/2690038/
2. Wait for the page to fully load
3. Observe the embed area — loading spinner appears and never resolves

Root cause: iframe elements are missing sandbox and allow attributes,
which blocks OpenProcessing's embed scripts from executing.

Would you like to work on the issue?

Yes, I have a fix ready and can open a PR immediately.