# 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