- CanvasArea: add useEffect to refresh InteractionEngine callbacks when props change
- App.tsx: handleElementCreated/Deleted/Modified now use functional setElements updates
- Root cause: CanvasArea init useEffect had empty deps, capturing stale callbacks at mount
- handleElementCreated used [...elements, el] with stale elements=[] closure
- Each new element replaced all previous ones instead of appending
- All 343 tests pass, tsc clean
Leopoldadmin