main scaled the girl 1.12x for every mac target (a white tile with a ring
reads small beside full-colour peers), but the macOS 26 layers were still
registered on the full-bleed squircle box, so macOS 26 would have shown a
smaller girl than macOS 15.
The layered icon's canvas is the plate itself, so derive its portrait box
from the mac box in plate coordinates. Ink overlap with the icns girl goes
from 0.65 to 0.996 IoU; only the two art layers change.
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