Proposed fix: Use OpenCode.

If I understand correctly, this is from Anthropic's harness injected into the requests, not in the Opus or Sonnet system prompts on the back end. Is that right?

Claude Managed Agents is different from Claude Code.

Not even close to the same thing though.

You can't use OpenCode if you have a subscription

OpenCode is not at all the same thing as Anthropic’s managed agents, and I’m under the impression that GP is paying API pricing.