[BUG] MCP: Emojis not supported in tool names

Environment

• Platform (select one):
• [X ] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.44 (Claude Code)
• Operating System: ProductName: macOS

ProductVersion: 15.5
BuildVersion: 24F74

• Terminal: Terminal app

Bug Description

When a MCP server has emojis in the tool name, Claude Code fails to handle any prompt.

Steps to Reproduce

1. Create an MCP server with emojis in the tool name.
2. Add the MCP server to Claude Code.
3. Try to run a prompt. Even if it has nothing to do with the MCP server.

Expected Behavior

It ignores the bad behaving MCP server and executes the prompt.

Actual Behavior

Claude fails to do anything and returns an error message that has no guidance on what to do:
⎿ API Error: 400 │
│ {"type":"error","error":{"type":"invalid_request_error", │
│ "message":"tools.15.custom.name: String should match pattern │
│ '^[a-zA-Z0-9_-]{1,128}$'"}}.

Additional Context

I don't have any logs, as even running claude --debug just provided this same error you see above.