- TopBar: EDIT ToggleButton, spaced from the REC/ON-AIR segments - MainViewModel: explicit EditingActive drives IsEditMode; YouTube go-live turns edit off, stop turns it on - SceneThumbnailStrip: tiles fixed 196x130 and centered; dark background fills the column so its edge does not move on resize; strip row fixed 154px - MainWindow: left column fixed at 360px; WIDTHS diagnostic log on resize Not pushed.