JetBrainsMono Nerd Font draws 10% of the em above the ascent Text
reserves for it (yMax 1120 against ascent 1020), and a patched or
user-chosen family can be worse. In normal flow that sliver costs
nothing; at the top of a clipping list it is sliced off and the header
renders beheaded.
Reserving it in PanelSectionHeader covers every panel at once, rather
than each list working around it in its own geometry.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
