GtkPaned clips each child to its allocation, so in split tabs the outer
focus and attention rings lost their top edge and corners. The rings are
now inset shadows (the gates glow inward), which still never change layout.
The attention pill also moves out of the header group that recedes on
unfocused panes: an approval stays loud wherever it is.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>