Window(icon = ...) only sets the in-title-bar proxy icon — it does NOT
drive the Cmd+Tab app switcher on macOS. That reads java.awt.Taskbar's
iconImage, which was never set, so gradle-run sessions showed the
generic Java coffee-cup square.
Load the PNG via ImageIO (preserves alpha), then set Taskbar.iconImage
before the application{} block starts. Guarded by isTaskbarSupported +
Feature.ICON_IMAGE so the call is a no-op on platforms without it.
Applies on all OSes that support the Taskbar API — macOS gets the dock
icon, GNOME/KDE get the task-switcher thumbnail, Windows gets the
taskbar icon.
https://claude.ai/code/session_01NufduPfZvYQVYwLkbCjCUo
Claude
9769bec472