[Bug] API Error 400: MCP tool_use.name exceeds 200 character limit, blocking all messages

Bug Description

After extended usage in a session, Claude Code becomes completely unresponsive to any input.
Every message (even simple ones like "hi") returns a 400 error indicating that a tool_use.name field exceeds the 200 character API limit.

The error references messages.35.content.1.tool_use.name, suggesting that a tool name in the conversation history is too long, likely from an MCP server with a long namespaced tool name.

Expected Behavior

Claude Code should either:

• Truncate or validate tool names before sending to the API
• Handle MCP tool names that approach the 200 character limit
• Provide a more actionable error message

Actual Behavior

Session becomes completely unusable. Any message returns:

API Error: 400
{"type":"error","error":{"type":"invalid_request_error","message":"messages.35.content.1.tool_use.name: String should have at most 200 characters"}}

Environment

• Version: 2.0.76
• Platform: macOS (darwin)
• Terminal: tmux
• Feedback ID: cb078242-4561-486a-b4de-0083c6c9f259

MCP list

claude-in-chrome
context7
playwright

Workaround

Starting a new conversation (/clear or new session) temporarily resolves the issue until long tool names are used again.

Screenshot

<img width="888" height="266" alt="Image" src="https://github.com/user-attachments/assets/de311077-c010-4949-a991-8a8efe9c52cc" />