Publishing HTML to SharePoint (OneUp HTML viewer)

SharePoint already hosts HTML: save an .html file into OneDrive or SharePoint and open it, and it renders in the OneUp HTML viewer — a sandboxed <iframe> under a strict Content-Security-Policy. There is no separate hosting service to provision; publishing is just writing an .html file to the user's drive as the signed-in user, then opening the file's webUrl.

This skill teaches an agent two things:

1. Author HTML that actually renders — the OneUp CSP + sandbox fail silently, so non-compliant HTML shows up blank or half-broken with no error. Follow the contract below and it just works.
2. Publish it — upload the file with Microsoft Graph (primary) or the SharePoint Vroom API (_api/v2.0, for agents already holding a SharePoint token), then hand the user the returned webUrl.