I've had that looping issue with open models too. But never 4.1. I wonder if it's a model + harness combo? But yeah, one loop issue and I'm done with a model forever.
So if you use MCP a lot, simplify the params, be more lenient on validation and rework the errors.
It is quite good with shell.
No mcp support. I'll try copying deepseek harness's basic tool call formats as a starting point.