The backdrop approach failed because a GTK4 window with no child widget
gets an empty Wayland input region, so pointer events passed straight
through it rather than being delivered to the GestureClick handler.
Replace with a single full-screen window (anchored to all 4 edges,
transparent background). The launcher UI (vbox) is 700 px wide,
halign=Center, valign=Start — visually identical to before. A
GestureClick on the window closes it when (x,y) falls outside the
vbox's allocation rectangle; clicks inside the vbox reach child widgets
normally and don't trigger the close path.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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