[rdrake]

Summary

On touch, a tap closed the image viewer only at the fitted size, so that a tap on a zoomed image would not throw it away. That also swallowed a tap on the backdrop beside a zoomed image, where at the fitted size the same tap closes.

 onTouchEnd
   tapped = one finger && barely moved && quick
-           && scale ≈ fitScale
+           && (scale ≈ fitScale || outsideImage(origin))   // the img's rect as drawn, zoom and pan included
   if tapped: closeViewer()

A tap on a zoomed image still does nothing; buttons and the open link keep their own taps; the mouse path is unchanged.

Evidence

• Before: tools/scenarios/image-viewer-back.mjs --mobile with the new step: FAIL a tap beside a zoomed image closes it.
  After:

  ok  a tap on a zoomed image leaves it open
  ok  a small pinch zooms in (1 → 1.5)
  ok  the zoomed image leaves backdrop beside it ({"x":1210,"y":750})
  ok  a tap beside a zoomed image closes it
  ok  a tap on ✕ closes the image
  ok  a tap at the fitted size closes the image
  

  The desktop run passes unchanged.
• Checked on an iPhone 16 in the iOS shell.
• Reviewed by Codex: no correctness issues; its two nits (scale compared to the fitted scale, comment wrapping) are in.

Merge Danger

Door: two-way

Blast Radius: image viewer

Touch closing only: a tap that lands off a zoomed image now closes it.