[Regression] "tools: Tool names must be unique" error when calling subagents in v2.0.30

Issue Description

When attempting to call any subagent using the Task tool, the API returns a 400 error with the message: "tools: Tool names must be unique."

This appears to be a regression of issue #703, which was fixed in v0.2.64.

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UPDATE: This is a duplicate of #10668, which has a more comprehensive analysis.

Closing in favor of #10668. Please see my comment there for additional information about Marketplace Plugins being affected.

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Environment

• Claude Code Version: v2.0.30
• OS: Windows 10 (10.0.19045)
• VSCode Version: (latest)
• Previous working version: v0.2.64 (per #703)

Configuration

.claude/settings.json:

{
  "plugins": [
    {
      "name": "backend-development",
      "marketplace": "claude-code-workflows",
      "enabled": true
    }
  ]
}

Steps to Reproduce

1. Enable any plugin from marketplace (e.g., backend-development)
2. Attempt to call a subagent using the Task tool:

``
Task(subagent_type="backend-development:backend-architect", prompt="...")
``

1. Error occurs immediately

Actual Behavior

API Error: 400 {
  "type":"error",
  "error":{
    "type":"invalid_request_error",
    "message":"tools: Tool names must be unique."
  },
  "request_id":"req_011CUeuizBxHEzd6xEsD1N4R"
}

The subagent call fails completely and cannot proceed.

Expected Behavior

The subagent should be invoked successfully, as it was in v0.2.64 according to #703.

Additional Context

• Tried with multiple subagent types: backend-development:backend-architect, general-purpose
• Same error occurs for all subagent types
• No custom MCP servers configured (only marketplace plugins)
• Issue #703 reported the same error with slash commands + MCP servers and was marked as fixed in v0.2.64
• This suggests a regression bug in v2.0.30

Related Issues

• #703 - Original issue fixed in v0.2.64
• #10668 - Comprehensive analysis of this regression (main issue)
• #10676 - Custom agents affected
• #10684 - MCP global permissions affected

Impact

This completely blocks the use of all subagents, which are core features of Claude Code workflows and plugins.

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Would appreciate any guidance or workaround while this is investigated. Thank you!