makeWorkersAiModel narrows the AI binding to one model's chat completion: the harness gets `complete`, not `run` on any model at any cost. gpt-oss-120b replies in the OpenAI shape (checked with a one-off probe), so the text is choices[0].message.content; anything else throws, naming the keys it got. Green: the model counts 3 rs in strawberry. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>