Filter 16: handle hosted-only tools in Chat Completions translation

[leseb]

Parent

Part of #35 (responses_to_chat_completions)

Context

The Responses API supports hosted tool types that have no Chat Completions equivalent:

• code_interpreter — sandboxed Python execution
• computer_use / computer_use_preview — screen automation
• image_generation — DALL-E image generation
• tool_search — tool discovery (gpt-5.4+)

When translating a Responses API request to Chat Completions format, the filter needs a strategy for these tools.

Decision needed

For each hosted-only tool type, choose one of:

1. Synthesize — create a function tool equivalent (like web_search/file_search), proxy intercepts and dispatches
2. Strip — remove from the tools array, log a warning
3. Reject — return an error if the request contains unsupported tools for the target backend

The strategy may differ per tool type (e.g., strip image_generation but reject computer_use).

Reference

• tool_parse (tool_parse: parse and register function/built-in tools #42) promotes has_code_interpreter, has_computer_use, has_image_generation, has_tool_search metadata for routing decisions
• Filter 16: synthesize function tool definitions for built-in tools #296 covers synthesis for web_search/file_search