Replace LaunchedEffect(startScreen) pattern with remember(startScreen) keyed recreation of NavBackStack. Mutating the same NavBackStack by clearing and re-adding entries confuses Navigation3's internal state, causing duplicate screen entries that compete for touch events. The fix creates a fresh NavBackStack whenever startScreen changes (chat -> landing), avoiding any stale-state mutation issues. Co-authored-by: M57 <hy4ri@users.noreply.github.com>