Duotone bar tells screen reader users to reposition stops, but positions are discarded #81799

Description

CustomDuotoneBar tells users they can reposition gradient stops, but the duotone data model has nowhere to store a position, so the instruction describes an operation that cannot take effect.

The control points render the shared ControlPoints announcement from CustomGradientBar:

Use your left or right arrow keys or drag and drop with the mouse to change the gradient position. Press the button to change the color or remove the control point.

packages/components/src/custom-gradient-picker/gradient-bar/control-points.tsx:68

But CustomDuotoneBar discards everything except the colors:

const newValue = getColorsFromColorStops( newColorStops );
onChange( newValue );

packages/components/src/duotone-picker/custom-duotone-bar.tsx:28

getColorsFromColorStops maps each stop to color and drops position. A duotone is two colors with no positions, so there is nothing to persist even in principle.

Impact

Screen reader users are instructed to perform an action that silently does nothing. Sighted users dragging a stop see it move and snap back on re-render. The keyboard instruction is the more serious half, since it is the only description of the control those users get.

This is pre-existing behaviour, not a regression. It is worth raising now because #81605 adds a Duotone tab to the Global Styles palette editor, so the same bar is reached from a second place and by more people.

Suggested direction

The positions cannot be made meaningful, so the announcement is what should change. Roughly:

• An opt-out on CustomGradientBar / ControlPoints — something like disablePositioning — that suppresses the position half of the instruction and the arrow-key handling, which CustomDuotoneBar would set.
• Or a dedicated announcement for the duotone case, describing only what actually works: press to change the color.

Either is an API change to custom-gradient-picker in service of a duotone-picker bug, which is why it did not belong in #81605.

Notes

Raised by @ciampo in review: #81605 (comment)