feat(studio): a finger across the photo is the open ruler's own track

docker/frontend/src/App.tsx

@@ -4720,6 +4720,16 @@ export function Workspace() {
           canCompare={!!source}
           onSaveOriginal={() => void saveOriginal()}
           onClear={() => setClearing(true)}
+          // The open ruler, handed to the stage as the track the photo itself
+          // becomes: a chip's ruler stands at the foot of a phone's screen, and
+          // the corner being judged is at the top of it, so a finger dragged
+          // across the picture moves the knob instead. STRAIGHTEN and TONE CURVE
+          // open no row (see `slider`), and neither hands anything over.
+          rulerDrag={
+            slider
+              ? { value: slider.value, min: slider.min, max: slider.max, step: slider.step, onChange: slider.onChange }
+              : null
+          }
           picking={picking}
           onPickColor={pickColor}
           brushTool={brushTool}