Gate on the window's shape, not on the platform

A screen that has two headers picks between them from one line, and that line reads the window:

val screenInfo = getScreenSizeInfo()
val isPortrait = screenInfo.wDP < screenInfo.hDP

"Portrait" here means this window is taller than it is wide — nothing about the device. The size accessor is per-platform (window metrics on mobile, container size on desktop) but it reports the window, so split-screen, a half-width desktop window and a rotated phone all move the same value and a recomposition follows each. A platform check answers none of those.

Everything that is not a choice between the two layouts stays outside the branch: the palette-derived page background and the blur source are applied to the list itself, unconditionally. Inside the branch is the header — and, where the wide header carries its own play/shuffle cluster, where that sits.

Traps