`titlebarAppearsTransparent` is not the app's to hold on a scene window: it is
the AppKit face of the tree's resolved `toolbarBackgroundVisibility`, and
SwiftUI writes it on every pass that re-applies a window's configuration. The
board stated nothing, so `.automatic` resolved and each pass put `false` back
over what `HostedWindowController` had set out of band — correct on open,
because the walk lands after the pass that follows window creation, and opaque
at the next one, with nothing to re-assert it since the board's own reading had
not changed. The board now declares the posture where SwiftUI will keep
asserting it; the AppKit write stays as the same value one turn earlier.
Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy
rzen
a429a7ec4d