DesignSync is always denied in Projects threads, but works in a regular Code tab session on the same machine

What happened
In Claude Desktop on Windows, every call to the built-in DesignSync tool from a Projects (Beta) thread is denied instantly, so a Claude Design handoff ("Use the claude_design MCP … auth via /design-login … Implement: <file>.html") cannot be completed in a Projects thread. The same call succeeds in a regular Code tab session on the same machine, with the same Claude Code version, account and settings.

Environment

• Claude Desktop, Windows 11 (10.0.26200), Code tab
• Claude Code 2.1.286 (transcript entrypoint: claude-desktop)
• Projects (Beta) threads running locally on this machine (Remote Control), permission mode auto

Steps to reproduce

1. Paste a Claude Design handoff instruction into a Projects thread that runs on this machine.
2. The thread loads DesignSync through tool search and calls it (list_files with the Claude Design project's ID).

Actual result

• Permission to use DesignSync has been denied. The transcript records toolDenialKind: "permission-rule".
• 12 attempts in 3 different Projects threads, each rejected within 5–10 ms (example: tool call at 18:47:56.202Z, denial at 18:47:56.208Z). No permission prompt is shown and the request never reaches Claude Design.
• This is not the auto mode classifier denial, which has its own message. The tool is still offered to the model in these threads; the denial happens only when it is called.

Expected result

DesignSync reads the project, or at least shows a permission prompt I can approve, as it does in a regular session.

What I already tried

• Added "DesignSync" to permissions.allow in %USERPROFILE%\.claude\settings.json. No deny rule exists in my user, project, local or managed settings.
• Ran /design-login in an interactive terminal session and approved it in the browser.
• Started a brand-new Projects thread after both steps: still denied on the first call.

Control test (works)

A regular Code tab session on the same machine (Claude Code 2.1.286, entrypoint: claude-desktop, same account and settings, permission mode bypassPermissions) ran DesignSync get_project and list_files on the same project successfully (2026-10-02, 19:06–19:07 UTC).

The two sessions differ in two ways: permission mode (auto vs bypassPermissions) and session type (Projects thread vs regular session). I have not isolated which of the two causes the denial.

Impact

Every Claude Design handoff in my Projects workflow is blocked. The workaround is to download the design as a ZIP by hand, or to open a separate regular session only to fetch the files.

Questions

1. Is DesignSync intentionally disabled in Projects threads or in auto mode? If so, what is the supported way to implement a Claude Design handoff from a Projects thread?
2. If it is not intentional, can it be fixed, or is there a setting that allows it?

Related

• #92215 (Claude Design first-party MCP returns 403) is a different symptom: there the request reaches the server, here it is denied locally before any request is made.

References (for log lookup)

• Filed from: Report a problem in Claude Code
• Project ID: chan_01R5SkKwajUDMc6CkgCMkHtt
• Thread ID: cmsg_01R5SkKwajUDMc6CkgCMkHttJyG8i3eZdwExHmj1uvxfmx
• Denied session (Projects thread): a25aed3e-82a8-480b-bcb0-e9ba2e7e3bd0, 2026-10-02 18:47–19:10 UTC
• Successful session (regular Code tab): 54f4343b-1057-4c42-b2ee-18189cc75e8a, 2026-10-02 19:06–19:07 UTC