Feature request: Add /v1/responses endpoint for OpenAI Responses API compatibility

[lengxii]

Background

OpenAI introduced the Responses API (POST /v1/responses) as a successor to Chat Completions. Tools like Codex CLI (wire_api = "responses") exclusively use this endpoint and cannot fall back to /v1/chat/completions.

Currently WindsurfAPI returns 404 Not Found for /v1/responses, which makes it incompatible with Codex and similar agents.

Proposed Solution

Add a /v1/responses endpoint that:

1. Accepts the Responses API request format (input field instead of messages, reasoning.effort, etc.)
2. Converts to the existing Chat Completions handler internally
3. Converts the CC response back to Responses API format (output array with type: "message" items)
4. Supports both streaming (SSE with response.created, response.output_text.delta, response.completed events) and non-streaming modes

Example Request

POST /v1/responses
{
  "model": "gpt-5-5-xhigh",
  "input": "Hello",
  "reasoning": {"effort": "high"},
  "stream": true
}

Example Response (non-streaming)

{
  "id": "resp-xxx",
  "object": "response",
  "model": "gpt-5-5-xhigh",
  "output": [
    {
      "type": "message",
      "role": "assistant",
      "content": [{"type": "output_text", "text": "Hi!"}],
      "status": "completed"
    }
  ],
  "usage": {...},
  "status": "completed"
}

This would make WindsurfAPI a drop-in replacement for Codex, Claude Code (already supported via /v1/messages), and standard Chat Completions clients.

I have a working implementation and can submit a PR if interested.

[dwgx]

合实施完了 commit 575c2d9 部到 US v2.0.4 上去了

src/handlers/responses.js 476 LOC + test/responses.test.js 245 LOC 36 个断言 121/121 通过

实测真上游：

非流式 input='用一句话讲个冷笑话' → 200 OK return response 对象 含 output[message] 和 usage{input_tokens,output_tokens,total_tokens}

流式 → 完整事件序列：
response.created → output_item.added → content_part.added → output_text.delta → output_text.done → content_part.done → output_item.done → response.completed

input/instructions/max_output_tokens/reasoning.effort 都 map 上了 function tools 复用 Chat Completions tools[] 上行 function_call/function_call_output round-trip 也工作

@sandleft #63 是同一根线 一起关 你们都用最新 master + Codex CLI wire_api="responses" 试试 还有问题贴 stream 截图重开