Codex auto-mirrors Claude Code marketplaces, breaking MCP handshake for Claude-only plugins

[Con-Benksl]

What version of Codex CLI is running?

v0.124.0

What subscription do you have?

pro 5x

Which model were you using?

No response

What platform is your computer?

macOS

What terminal emulator and version are you using (if applicable)?

Terminal.app

What issue are you seeing?

Problem

Codex CLI scans for .claude-plugin/marketplace.json files and
auto-imports any marketplace it finds into ~/.codex/.tmp/marketplaces/,
even when the marketplace is not declared in ~/.codex/config.toml.

When those marketplaces contain plugins designed only for Claude Code
(using ${CLAUDE_PLUGIN_ROOT} in .mcp.json — e.g., claude-mem),
Codex tries to launch their MCP servers at startup. Because Codex does
not substitute ${CLAUDE_PLUGIN_ROOT}, the command resolves to an
invalid path and the MCP handshake fails.

Reproduction

1. Install Claude Code and add a marketplace that ships a plugin with
   ${CLAUDE_PLUGIN_ROOT} in its .mcp.json (e.g. thedotmack/claude-mem).
2. Install Codex CLI. Do not declare the marketplace in config.toml.
3. Start Codex.
4. Observe:
   ⚠ MCP client for mcp-search failed to start:
   MCP startup failed: handshaking with MCP server failed:
   connection closed: initialize response

The offending directories ~/.codex/plugins/cache/thedotmack/ and
~/.codex/.tmp/marketplaces/thedotmack/ appear even though the user
never added thedotmack to their Codex config.

Workaround

Users currently have to either:

• Delete the mirrored cache (will be re-created on next start), or
• Add [plugins."<name>@<marketplace>"]\nenabled = false to config.toml
  for every leaked plugin

Neither scales as the user installs more Claude Code plugins.

Requested fix (any of)

1. Add a config.toml flag to opt out of Claude-marketplace discovery:

[plugins]                                                                                                                                                      
auto_discover_claude_marketplaces = false                                                                                                                    
2. Skip any plugin whose .mcp.json references ${CLAUDE_PLUGIN_ROOT}
(or any unresolved variable) instead of attempting the handshake.                                                                                              
3. Only import marketplaces explicitly listed in config.toml.    
                                                                                                                                                               
Environment                                                                                                                                                    
                                                                                                                                                               
- Codex CLI: <your version — run codex --version>                                                                                                              
- OS: macOS 15.4.0 / Darwin 25.4.0 (arm64)                                               
- Claude Code installed: yes 

### What steps can reproduce the bug?

**Summary**                                                                              
                                                                                                                                                               
Codex CLI auto-mirrors Claude Code marketplaces into `~/.codex/.tmp/marketplaces/` even when the marketplace is **not** declared in `~/.codex/config.toml`.    
When those marketplaces contain Claude-Code-only plugins (whose `.mcp.json` references `${CLAUDE_PLUGIN_ROOT}`), Codex tries to start their MCP servers at     
launch, and the handshake always fails because Codex does not substitute that variable.                                                                        
                                                                                         
**Steps to reproduce**                                                                                                                                       
                                                                                                                                                             
1. Install Claude Code and install a plugin that uses `${CLAUDE_PLUGIN_ROOT}` in its `.mcp.json` — e.g. `claude-mem` from the `thedotmack` marketplace         
(https://github.com/thedotmack/claude-mem).
2. Install Codex CLI (`@openai/codex` v0.124.0). Do **not** add `thedotmack` to `~/.codex/config.toml`.                                                        
3. Launch Codex.                                                                                                                                               
4. Observe startup errors:            
   ⚠ MCP client for mcp-search failed to start:                                                                                                                
     MCP startup failed: handshaking with MCP server failed:                                                                                                   
     connection closed: initialize response                                                                                                                    
5. Check the filesystem:                                                                                                                                       
- `~/.codex/plugins/cache/thedotmack/claude-mem/12.3.9/` exists                                                                                                
- `~/.codex/.tmp/marketplaces/thedotmack/` exists                                                                                                              
- Neither was ever declared in `config.toml` — they were mirrored from `~/.claude/plugins/marketplaces/thedotmack/`.                                           
                                                                                                                                                               
**Root cause (from strings inspection of the Codex binary)**                                                                                                   
                                                                                                                                                               
The Rust module `core-plugins/src/marketplace_upgrade.rs` scans for `.claude-plugin/marketplace.json` files and registers them as Codex marketplaces. There is 
no config flag to opt out.                                                                                                                                     
                                                                                         
---                            

### What is the expected behavior?

Codex should only load marketplaces that the user has explicitly declared in `~/.codex/config.toml`. Specifically, any of the following would fix the problem:
                                                                                                                                                               
1. **Preferred:** add an opt-out config flag:                                                                                                                  
   ```toml                                                                                                                                                     
   [plugins]                                                                                                                                                   
   auto_discover_claude_marketplaces = false                                                                                                                   
                                                                                                                                                             
2. Alternative: when Codex finds an MCP server whose command references an unresolved variable like ${CLAUDE_PLUGIN_ROOT}, skip it with a warning instead of   
attempting a doomed handshake.                                                           
3. Minimal: only import marketplaces that the user has explicitly added, and treat .claude-plugin/marketplace.json discovery as purely advisory.               
                                                                              

### Additional information

```markdown                                                                                                                                                  
**Current workaround**
                                                                                                                                                               
Adding this to `~/.codex/config.toml` for every leaked plugin:                                                                                                 
```toml                                                                                                                                                        
[plugins."claude-mem@thedotmack"]                                                                                                                              
enabled = false                                                                          
This doesn't scale — users who install more Claude Code plugins keep hitting new handshake failures.                                                         
                                                                                                                                                               
Environment
                                                                                                                                                               
- Codex CLI: codex-cli 0.124.0                                                                                                                                 
- OS: macOS 15.4.0 / Darwin 25.4.0 (arm64)
- Claude Code installed: yes                                                                                                                                   
- Affected plugin in my setup: claude-mem@thedotmack (12.3.9)                            
                                                                                                                                                               
Related GitHub MCP issue (may or may not be the same root cause)                                                                                               
                                                                                                                                                               
On the same setup, the built-in github@openai-curated plugin also fails to start, with:                                                                        
⚠ GitHub MCP does not support OAuth. Log in by adding a personal access token...         
This is a separate error but the user experience is the same — two startup warnings before any work begins.                                                    
                                                                                                                                                               
---