Rich HTML Artefact Delivery

html-rich-communication owns creation and local verification. This overlay owns only the final delivery boundary.

1. Require a locally rendered index.html with no material desktop/mobile defect.
2. Create a secret gist with gh gist create; do not pass --public.
3. Read the gist back with gh api and require public: false.
4. Return https://gistpreview.github.io/?<gist-id>.
5. Stop. Do not reopen the hosted preview unless the user reports a delivery defect or the page depends on host-specific script execution.

Prefer a genuinely self-contained file, but do not inline multi-megabyte runtimes. Render diagrams to static SVG. If packaging requires installing a browser framework or writing a custom bundler, the artefact is not in the default delivery lane.

If the hosted preview is blank, stale, or incompatible, stop this overlay and use html-artifact-publishing.