OpenAI bridge drops Claude Code tool calls #8

Description

Claude Code requests routed through an openai/* model work for text-only turns, but tool calls do not round-trip through the Messages/Responses bridge. When Codex returns a function_call, the bridge drops it and Claude Code receives an empty response with stop_reason: "end_turn".

Multi-turn tool transcripts also use invalid Responses input shapes: function_call and function_call_output are nested inside message content, and assistant text is encoded as input_text.

Steps to reproduce

1. Configure an OpenAI subscription account and an openai/* model.
2. Ask Claude Code to perform a task that requires a tool, such as reading a file.
3. Let the request continue into the tool-result turn.

Expected behaviour

• Codex function_call output is returned to Claude Code as an Anthropic tool_use block.
• The following tool_result is sent back as a top-level Responses function_call_output item using the same call_id.
• Streaming and non-streaming responses preserve text/tool ordering and return stop_reason: "tool_use" when a tool is requested.

Actual behaviour

The response mapper keeps text items only, so function calls disappear. On the next turn, the request converter nests call/result items inside message content; the Codex backend rejects that shape with HTTP 400.

Environment

• OS: macOS 26.5
• Node.js version: v26.4.0
• cc-router version: 0.6.2 (main)
• Mode: standalone

Logs

No proxy error is emitted for the dropped response item. The invalid follow-up request is rejected by the Codex backend with HTTP 400 invalid_value.