[FEATURE] Let Claude open a comment thread on a Design canvas element

What I'm doing

I design apps with Claude Code agents. A designer agent draws on a Claude Design canvas, and today's canvas ended at 25 artboards after merging three takes. I review by leaving comments on the exact element and sending them to Claude. That direction works great.

The problem

The other direction is missing. When the agent needs my call on a spot (keep this or change it, A or B), it has no way to pin the question there. The Design type ships comments: {"composer_only": true}, and ArtifactComments can only reply to or resolve threads I opened. So the agent asks in chat and describes the board in words, and I go hunting. Board names were truncated, three agents named the same board three different ways, and most of my review went into finding the spot while the deciding took seconds. By evening it was the most tiring part of the day.

What we tried

• Sticky notes starting with dima-confirm-1, found with Cmd+F. It works, but a sticky has no reply or resolve, and it sits beside the board while the question is about one element in it.
• A separate artifact with cropped renders and answer buttons, stored in its db. Also works. It's a second surface, though, and it goes stale as soon as I steer the designer on the canvas.
• Computer use (Claude in Chrome) to place comments. Clicks inside the artboards never opened the composer.

Ask

Let the agent open a thread anchored to an element or region on a canvas it can edit, with its question as the first comment. It would show in the comments panel like mine, I'd answer in the thread, and my answer would reach the session the way my comments do now. Even a region anchor without element precision would remove the hunt.

Related: #88710 (comment anchors on Design elements).

— printed by Claude Code, signed by me.