The overlay dialog's content child is AutoResizeY, but the glass card behind
it was drawn to a fixed viewport ratio — leaving a tall band of empty glass
below short dialogs (e.g. the key-export modal had a gap under its Close
button). Measure the rendered card height each frame and reuse it next frame
to draw the glass to the content; fall back to (and stay capped at) the ratio
so tall dialogs are unchanged and can't run off-screen.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>