Classroom performance:
- WebSocket server (ws-server.js) for low-latency cursor & stroke preview
Replaces HTTP POST per event → eliminates per-message auth overhead
Session member cache (30s TTL) avoids SQLite query per WS message
Fallback to HTTP POST when WS not connected
- Cursor throttle reduced 100ms → 33ms (~30fps)
- Stroke preview throttle reduced 50ms → 20ms
- whiteboard.js: render() is now rAF-gated (_doRender/_rafPending)
Multiple render() calls within one frame collapse into one repaint
document.hidden check — zero CPU when tab is in background
visibilitychange listener restores canvas on tab focus
Guest board:
- guestClassroom.js route: public token-based read-only access
- guest-board.html: name entry + read-only whiteboard + SSE
- SSE: addGuestClient/removeGuestClient/emitToGuests
Screen share picker:
- Discord-style modal with tab switching (screen/window/tab)
- Live video preview before confirming share
- useExistingScreenStream() in ClassroomRTC
Fullscreen exit overlay:
- #cr-fs-exit-overlay button inside cr-board-wrap
- Visible only via CSS :fullscreen selector (touchpad users)
File sharing from library:
- Teacher picks file from library, sends as styled card in chat
- crDownloadLibraryFile() fetches with Bearer auth
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Maxim Dolgolyov
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