- Support ephemeral cursor_moved and client_left events in docroom Hub
- Keep active in-memory cursor presence map per document room
- Synchronize current presence state to newly connected WebSocket clients
- Allow read-only viewers to share cursor positions without document mutation rights
- Throttle frontend cursor move emissions to 100ms with instant blur cleanup
- Render active collaborator presence avatar pills in document header
- Display user-colored block indicator and non-destructive caret overlay with name tag
