~/safe
Every app runs sealed off. It can only see its own folder and can only talk back to your files. It cannot reach the internet, read your other apps' data, or send anything anywhere. That is enforced by the system, and visible in your browser's own dev tools. Not a promise on a trust page.
Why it matters
The reason you can't just run a random HTML file someone made is that you have no idea what it does with your data. General Text answers that structurally rather than by reputation, which is what turns a pile of one-off tools into something you can actually share, read, and build on.
What an app cannot do
See it for yourself. Open your browser's dev tools while an app runs and watch a blocked request to anywhere else. The guarantee made visible is the whole point.