OpenAI Reasoning Proxy Spec

Goal

Provide a single-file FastAPI proxy that exposes an OpenAI-compatible POST /v1/chat/completions endpoint while translating reasoning controls to LM Studio native POST /api/v1/chat.

Scope

Implemented as one Python file.
Supports:
- GET /healthz
- GET /v1/models
- POST /v1/chat/completions
Accepts OpenAI-style reasoning and enable_thinking.
Translates them to LM Studio native reasoning: "on" | "off".
Converts native LM Studio output back into OpenAI-style choices[0].message.

Behavior

reasoning: "off" wins over enable_thinking.
If enable_thinking is provided:
- false => native reasoning: "off"
- true => native reasoning: "on"
If neither is provided, default to native reasoning: "on".
stream=true is rejected for now.

Message Mapping

OpenAI system messages are merged into native system_prompt.
Other messages are flattened into a plain-text transcript:
- User: ...
- Assistant: ...
This preserves basic chat context without depending on undocumented native message schemas.

Verification

Unit tests cover payload mapping and native-to-OpenAI response translation.
Real integration test confirmed:
- baseline => reasoning on
- enable_thinking: false => reasoning off
- reasoning: "off" => reasoning off
- reasoning: "on" => reasoning on