Subagent launch fails with 'Tool names must be unique' when MCP server is configured

Description

When an MCP server (particularly chrome-devtools) is configured, attempting to launch any subagent (Task tool) results in the following error, preventing subagent execution:

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."},"request_id":"req_..."}

Environment

• Claude Code Version: 2.0.30
• OS: macOS (Darwin 24.6.0)
• Configured MCP Servers: chrome-devtools, filesystem

Steps to Reproduce

1. Configure an MCP server in claude_desktop_config.json (e.g., chrome-devtools)

``json
{
"mcpServers": {
"chrome-devtools": {
"command": "npx",
"args": ["chrome-devtools-mcp@latest"]
}
}
}
``

1. Launch Claude Code

1. Attempt to launch any subagent

``
Task tool with subagent_type: rspec-runner, lint-fixer, code-reviewer, etc.
``

1. Error occurs

Expected Behavior

Subagents should launch successfully even when MCP servers are configured.

Actual Behavior

Subagent launch fails with "Tool names must be unique" error.

Root Cause Analysis

The issue appears to be caused by tool name conflicts between:

• Tools provided by MCP servers (e.g., mcp__chrome-devtools__*)
• Tool definitions during subagent initialization

These tools seem to be registered twice, causing the duplicate name error.

Workaround

Currently, the only workaround is to disable MCP servers, which allows subagents to function properly.

Related Issues

• #703 - Slash Command registration collision with MCP Server Configuration (fixed in v0.2.64)
• This appears to be a similar issue affecting subagents

Impact

All subagent types are affected by this issue:

• rspec-runner
• lint-fixer
• code-reviewer
• chrome-devtools
• temporary-script-runner
• serena-expert
• etc.