Read Receipts / Unread Badges

Track lastSeenRowKey / lastSeenAt per user per room to show per-room and per-DM unread counts.

Why not

Read-receipt semantics do not fit a casual, always-scrolling UX.
Background Postgres writes on every room switch / focus add noise for little gain.

Allowed narrower version: mention-only counts are fine and shipped as mention badges: count chips for @mentions only, with a single per-room counter and no per-message read tracking.

Keyword notification rules

Rejected — per-user custom keyword pings beyond @mentions.

Starred messages

Rejected — per-user bookmarked messages with a Saved view.