Server findings:
- Synapse 1.153.0 is FULLY UP TO DATE (latest as of 2026-05-19)
- MSC4140 (scheduled msgs), MSC3771 (thread receipts), MSC4133 (extended profiles)
all CONFIRMED supported via unstable_features flags
- MSC3892 (reaction redaction), MSC3266 (room summary) BLOCKED — not supported
- MSC4306 (thread subscriptions) BLOCKED — not supported
Upstream Cinny confirms (removed from build queue):
- Back to Latest button (RoomTimeline.tsx:2180), Mark rooms as read (Home.tsx:73),
Tombstone/upgrade banner (RoomTombstone.tsx), Speaking indicator (useCallSpeakers.ts),
Spoiler rendering (ImageContent/VideoContent — blur+click-reveal), Report message
Architecture facts documented:
- AvatarImage child constraint (no children — wrap externally)
- Sidebar translateX blocks backdrop-filter
- EC bridge: no participant events (use m.call.member state events instead)
- No in-app toast system (must build from scratch)
- Voice player at AudioContent.tsx:44, notification sounds hardcoded in ClientNonUIFeatures
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>