Let Claude Code talk to the Claude Design agent (same desktop app, no bridge)

Context

Claude Desktop, Code tab, using the bundled /design-sync skill and the DesignSync tool against a Claude Design design-system project.

Problem

Claude Code can upload a design system to a Claude Design project (DesignSync), but it cannot:

• send a prompt to the Claude Design agent working on a canvas in that project,
• read a canvas (.dc.html) or the design agent's report,
• read reviewer comments left on a canvas.

So the workflow for a spec-driven mockup is: Claude Code writes a prompt, the user copies it by hand into Claude Design, the design agent works, the user copies the report back into Claude Code, which updates the spec and writes the next prompt. In one afternoon we did this round trip six times for one canvas (57 artboards), only to fix data and copy details Claude Code already knew from the spec.

Both agents run in the same desktop app, but there is no bridge between them. /design in the Code tab only manages consent (/design consent / /design revoke); after granting it, no new tool appears in the session.

Ask

A two-way channel between the two agents in the same app. Minimum useful version:

1. Claude Code can post a message to a Claude Design project conversation and receive the agent's reply (like SendMessage between Claude Code sessions).
2. Claude Code can read a canvas file and its comments through DesignSync (get_file already exists for design-system projects; extend it to design projects and to comments).
3. Optional: /design-sync could register the spec (our ux.md) as the canvas brief, so both agents share one source of truth.

Why it matters

The point of /design-sync is that the design agent builds with the real components. The next step, keeping the canvas and the spec in sync, is still a copy-paste loop a person has to drive by hand.

Environment

• Claude Desktop (Windows 11), Code tab
• Claude Code 2.1.284 (bundled skills path), model Fable 5.1
• /design-sync run against a package-shaped repo (no Storybook), 93 components, upload verified