[BUG] Adobe for Creativity plugin: Dynamic Client Registration rejected (HTTP 403)

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

/mcp 실행 시 plugin:adobe-for-creativity:Adobe for creativity 서버가 "Needs Auth" 상태로 뜸
Authenticate 클릭 시 에러: SDK auth failed: Dynamic Client Registration rejected (HTTP 403)
재현 방법: /mcp → Adobe for creativity → Authenticate
OS: Windows 11
매번 재현됨 (Retry해도 동일한 에러)

### What Should Happen?

The Adobe for Creativity plugin should authenticate successfully via OAuth, and the MCP server should connect without errors.

### Error Messages/Logs

```shell

```

### Steps to Reproduce

1. Open Claude Code and run `/mcp`
2. Select the "plugin:adobe-for-creativity:Adobe for creativity" MCP server (status shows "Needs Auth")
3. Click "Authenticate"
4. Error appears: "SDK auth failed: Dynamic Client Registration rejected (HTTP 403)"

Note: This happens every time, on every attempt to authenticate this plugin. OS: Windows 11.

### Claude Model

None

### Is this a regression?

I don't know

### Last Working Version

_No response_

### Claude Code Version

2.1.236 (Claude Code)

### Platform

Anthropic API

### Operating System

Windows

### Terminal/Shell

VS Code integrated terminal

### Additional Information

_No response_

Reproduce on Windows 11 with Claude Code 2.1.236 by running /mcp, selecting the Adobe for Creativity server, and choosing Authenticate. Trace the reported Dynamic Client Registration HTTP 403 from that authentication entry point; done means OAuth authentication succeeds and the MCP server connects without errors.

Written by the indexing model from the issue text.