[BUG] Claude displays optional nullable MCP parameters as `unknown`

Environment

• Platform (select one):
• [X] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.81
• Operating System: Windows 10
• Terminal: cmd

Bug Description

When displaying the description of an MCP Tool, claude-code shows the type of optional parameters as unknown instead of the actual type. E.g.

// max_results schema:
{
    "anyOf": [
        { "type": "integer" },
        { "type": "null" }
    ],
    "default": null,
    "description": "Maximum results to return",
    "title": "Max Results"
}

<img width="976" height="720" alt="Image" src="https://github.com/user-attachments/assets/c648cc26-d0a1-4327-9eda-43ee01fa19f3" />

Steps to Reproduce

1. Add the https://github.com/ast-grep/ast-grep-mcp MCP server
2. Launch claude-code
3. Inspect the ast-grep mcp server tools (find_code or find_code_by_rule) via the /mcp command

Expected Behavior

The parameter type is rendered as integer | null or integer? or since required parameters are already marked with (required) it might also be enough to simply render the type as integer.

Actual Behavior

claude-code displays the parameter type as unknown

Additional Context

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