## 4.4 Implementation - Global Exception Handling (FastAPI)

Claude Code MUST implement global exception handling using FastAPI decorators.

---

### Step 1: Import

    from fastapi import Request, HTTPException
    from fastapi.responses import JSONResponse
    import traceback

---

### Step 2: Handle HTTPException

    @app.exception_handler(HTTPException)
    async def http_exception_handler(request: Request, exc: HTTPException):
        request_id = getattr(request.state, "request_id", "-")

        api_logger.warning(
            "[%s] %s %s %s %s",
            request_id,
            request.method,
            request.url.path,
            exc.status_code,
            str(exc.detail),
        )

        return JSONResponse(
            status_code=exc.status_code,
            content={
                "message": str(exc.detail),
                "request_id": request_id,
            },
        )

---

### Step 3: Handle Unhandled Exception

    @app.exception_handler(Exception)
    async def global_exception_handler(request: Request, exc: Exception):
        request_id = getattr(request.state, "request_id", "-")

        tb = "".join(traceback.format_exception(type(exc), exc, exc.__traceback__))

        api_logger.error(
            "[%s] %s %s unhandled exception\n%s",
            request_id,
            request.method,
            request.url.path,
            tb,
        )

        return JSONResponse(
            status_code=500,
            content={
                "message": "Internal server error",
                "request_id": request_id,
            },
        )

---

### Step 4: Requirements

- MUST use `@app.exception_handler`
- MUST NOT let exceptions go unlogged
- MUST include request_id in all logs
- MUST include traceback for ERROR logs
- MUST NOT expose traceback in response