Add OpenAI Responses-compatible endpoint

[CUHKSZzxy]

Summary

• Add a text-first OpenAI Responses-compatible POST /v1/responses endpoint.
• Support string/message input, instructions/developer-role normalization, function tools, tool choice validation, and Responses SSE events.
• Add focused tests, Responses API docs, and Codex integration docs.

Validation

• pytest tests/test_lmdeploy/serve/openai/test_responses.py -q (18 passed)
• git diff --check upstream/main...HEAD
• Local Codex smoke tests against LMDeploy for no-tool, read, edit, multi-step, and project workflows.

Codex Demo

[Copilot]

Pull request overview

This PR adds a text-first, OpenAI Responses API–compatible endpoint (POST /v1/responses) to LMDeploy’s OpenAI server, including request normalization (string/messages/instructions/developer role), function tool mapping/tool-choice validation, and an SSE streaming event surface. It also updates middleware route protection, integrates the new router into api_server, and adds tests + documentation (including Codex integration docs).

Changes:

• Add lmdeploy/serve/openai/responses.py implementing POST /v1/responses (non-stream + SSE streaming) and related request/response models.
• Wire the new endpoint into the OpenAI API server and protect it under engine-sleep middleware.
• Add focused unit tests plus English/Chinese documentation and integration guides (Codex / Claude Code).

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/test_lmdeploy/serve/openai/test_responses.py	Adds unit coverage for input normalization, tools/tool_choice validation, response shapes, and SSE event shapes.
lmdeploy/serve/utils/server_utils.py	Adds /v1/responses to sleeping-engine protected inference routes.
lmdeploy/serve/openai/responses.py	Implements the Responses-compatible router, request parsing, tool conversion, non-stream response construction, and SSE streaming events.
lmdeploy/serve/openai/api_server.py	Registers the new Responses router on the FastAPI app.
docs/zh_cn/llm/api_server.md	Links to the new Responses endpoint documentation.
docs/zh_cn/llm/api_server_responses.md	Documents the /v1/responses endpoint (Text V1 subset), tools, SSE events, and Codex setup notes.
docs/zh_cn/index.rst	Adds the Responses doc page to the Chinese toctree.
docs/en/llm/api_server.md	Links to the new Responses endpoint documentation.
docs/en/llm/api_server_responses.md	Documents the /v1/responses endpoint and points to Codex integration docs.
docs/en/integration/codex.md	Adds a Codex → LMDeploy /v1/responses integration guide.
docs/en/integration/claude_code.md	Adds a Claude Code → LMDeploy /v1/messages integration guide.
docs/en/index.rst	Adds the Responses doc page and a new Integrations toctree (Codex/Claude Code).

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