Phase C.1 of the protocol-gaps roadmap, gate-green (693 tests). Generalizes the
Element Call widget host into a general room-widget feature:
- StateEvent.Widget + widgetsPanelAtom + useRoomWidgets (WidgetParser).
- RoomWidgetView: sandboxed-iframe host via ClientWidgetApi with a conservative
GeneralWidgetDriver (approves only benign display caps — no room-event
send/read/to-device). Blocks same-origin widget URLs (sandbox breakout guard).
- WidgetsPanel: list / open / add / remove, PL-gated on im.vector.modular.widgets,
https + non-same-origin URL validation. Mounted like the media gallery (header
toggle + 3-way content-panel exclusivity + mobile full-screen overlay).
- Tested URL/capability/id helpers.
Requires the prod CSP frame-src widening (matrix repo) for external widgets.
v1 cuts (capability consent prompt, Jitsi/sticker types, user widgets) noted.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
