This change adds additionalProperties = false to the tool_input schema for the use_mcp function to satisfy strict JSON schema requirements and resolve invalid schema errors when using GPT-5.x on GitHub Copilot. It enforces tighter validation for nested objects, prevents unexpected properties, and ensures tests and tooling pass cleanly. However, the stricter schema may break existing calls that relied on passing extra or dynamic fields in tool_input and could necessitate updates to client code or documentation.