claude-design MCP: "needs_project_grant" error has no approval UI anywhere, and now blocks previously-writable projects too

Summary

Calls to the claude-design MCP tools (write_files, copy_files) fail with a needs_project_grant error whose payload describes a one-time approval prompt that is never actually rendered anywhere — not in the calling client, not in claude.ai/design Settings, not on the project page itself. This started out affecting only brand-new projects, but during the same session it began blocking writes to a project that had been successfully written to minutes earlier.

Error payload

{"error":"needs_project_grant","project_id":"<id>","prompt":"Allow Claude to edit this project? This lasts until you revoke it at claude.ai/design/settings."}

Steps to reproduce

1. From Claude Code, use mcp__claude-design__write_files or copy_files against a Claude Design project.
2. First write to a new project returns needs_project_grant as above — expected, per the tool's own description ("the first write... prompts a one-time approval").
3. No approval UI appears anywhere:

• Not inline in the Claude Code/chat session that issued the call.
• Not in claude.ai/design/settings (checked — only a general "Claude product access" On/Off toggle exists there, already On, no per-project list or pending-approval entries).
• Not on the project's own page (https://claude.ai/design/p/<id>) — opened it directly, no prompt/banner appeared.

1. Manually duplicating the project in the Claude Design app (as a workaround) does not help — the duplicate hits the same needs_project_grant error on first write.
2. Unexpectedly, a project that had been written to successfully earlier in the same session (multiple write_files/delete_files calls succeeded) later failed with the same needs_project_grant error on a subsequent write attempt, with no configuration change in between.

Expected behavior

Either:

• The approval prompt described in the error's prompt field should render as an actionable UI element somewhere the user can actually click (in the originating chat surface seems most natural, per the tool's phrasing), or
• If a grant already exists for a project (as evidenced by prior successful writes in the same session), it shouldn't need re-approval without any explicit revocation.

Actual behavior

• No UI surface renders the approval prompt at all, in any context tried.
• The grant appears to silently lapse/reset even mid-session, without the user revoking anything at claude.ai/design/settings.
• This makes any MCP-driven Claude Design workflow (e.g. building on a template project via copy_files) unusable once it touches a project that hasn't very recently been granted — with no way to grant it.

Environment

• Claude Code (Windows), claude-design MCP tools (list_projects, list_files, read_file, write_files, copy_files, finalize_plan, create_project)
• Checked Anthropic's public docs (Claude Design help center articles) — no mention of this grant mechanism, the approval prompt, or how to trigger/view it.

Additional context

Searched for prior reports of this specific error — found none. Related but distinct: #69313 and #69325 report the claude_design MCP server itself failing with HTTP 404, which may point to broader instability in this integration, though the symptom differs from the grant issue described here.