Ghostty adds its IOSurface layer to the viewport on iOS and never removes
it when the surface is freed, so a theme or font refresh stacked the new
layer over the stale one. Once the new layer shrinks to a smaller shared
grid, the old frame shows as a gutter. Remove the viewport's sublayers
after freeing the surface.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>