Adapters Overview

VernLLM expects a client shaped roughly like OpenAI's chat.completions.create, its own LLMClient interface, not a copy of OpenAI's actual SDK types. Some providers already match closely enough to need no adapter; others need one that translates their native API into it. A few fields (ContentBlock[] multimodal input, is_error on tool messages) are VernLLM's own additions with no OpenAI equivalent, adapters translate those as needed per provider too.