[BUG] MCPSearch usage breaks Haiku

Preflight Checklist

• [x] I have searched existing issues 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?

Using MCP Server tools with Haiku is broken, because Claude tries to use the MCPSearch tool. Whenever this happens an API error is returned. This used to work and did not utilized the MCPSearch before.

What Should Happen?

Do not use MCPSearch with Haiku model, otherwise it loses ability to use MCP provided tools.

Error Messages/Logs

MCPSearch(Search MCP tools: "select:mcp__chroma-mcp__chroma_query_documents")
  ⎿  Found 1 tool
  ⎿ API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"'claude-haiku-4-5-20251001' does 
    not support tool_reference blocks. This feature is only available on Claude Sonnet 4+, Opus 4+, and newer 
    models."},"request_id":"xxx"}

Steps to Reproduce

1. Connect MCP tools to claude code.
2. Configure claude code to always use Haiku model (also for agents)
3. Prompt Claude to use an MCP tool. See error when it uses MCPSearch to find a tool.

Claude Model

Other

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.0.64 (maybe also a higher version)

Claude Code Version

2.0.75

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_