MCP tool with invalid JSON Schema property key breaks entire session irrecoverably

Description

When an MCP server exposes a tool whose input schema contains a property key with characters outside the pattern ^[a-zA-Z0-9_.-]{1,64}$ (e.g., $.xgafv from Google APIs), the Anthropic API returns a 400 error. This is expected validation behavior, but the failure mode is catastrophic: the entire Claude Code session becomes permanently unusable.

Reproduction

1. Configure an MCP server that exposes a tool with a property key containing $ (or any char outside [a-zA-Z0-9_.-])
2. Use ToolSearch to load that tool into the session
3. Every subsequent prompt — including completely unrelated ones like "hello" — fails with:

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.42.custom.input_schema.properties: Property keys should match pattern '^[a-zA-Z0-9_.-]{1,64}'"}}

1. The only recovery is /clear to reset the conversation context

Issues

1. Session-breaking failure mode: A single invalid tool poisons the entire tool list, which is sent with every API request. There's no way to unload it or recover without clearing the session.

1. No graceful degradation: The API could reject/skip the individual invalid tool rather than failing the entire request. Alternatively, Claude Code could catch this error and remove the offending tool from the active set.

1. Unhelpful error message: The error says tools.42 (by index) but doesn't identify the tool name or the specific invalid property key, making debugging difficult.

Expected behavior

• Invalid MCP tool schemas should not break the entire session
• At minimum, Claude Code should detect this error pattern and either remove the offending tool or inform the user which tool is problematic
• Ideally, the API would skip invalid tools and proceed with the valid ones

Environment

• Claude Code CLI (claude-opus-4-6)
• Linux
• MCP server: locally generated server for Google Drive API (parameter $.xgafv has $ in property key)