Add request-scoped logging middleware with UUID request IDs

[mattmorgis]

Context

Our current logging is a single global basicConfig() call that prints naïve human-readable lines. For production-ish usage (even for a hobby project) we need:

1. A unique request ID so we can correlate all log entries that belong to the same HTTP request.
2. A single access-log line per request that captures method, path, status and latency.
3. The request ID returned to the caller via an X-Request-ID header so they can quote it in bug reports.
4. No new external dependencies (project requirement) – stick to stdlib + FastAPI.

Task

Create a new module app/logging_config.py that provides both logging configuration and a FastAPI middleware for request IDs. Then wire it into app/main.py.

Implementation details

1. Context var & filter
   • Create a contextvars.ContextVar named _request_id_ctx that stores a str | None.
   • Implement class RequestIdFilter(logging.Filter); filter() should set record.request_id to the current value or "-".

2. configure_logging()
   • Call logging.basicConfig() with:

   level=logging.INFO,
   format="%(asctime)s [%(levelname)s] [%(request_id)s] %(name)s: %(message)s",

   • Register the RequestIdFilter on the root logger (logging.getLogger().addFilter(...)).

3. Middleware

   def add_request_id_middleware(app: FastAPI) -> None:
       @app.middleware("http")
       async def _request_id_middleware(request: Request, call_next):
           import uuid, time, logging
           req_id = uuid.uuid4().hex
           token = _request_id_ctx.set(req_id)
           start = time.perf_counter()
           try:
               response = await call_next(request)
           finally:
               duration_ms = int((time.perf_counter() - start) * 1000)
               logging.getLogger("app.access").info(
                   "%s %s %s (%d ms)",
                   request.method,
                   request.url.path,
                   response.status_code if "response" in locals() else "ERR",
                   duration_ms,
               )
               _request_id_ctx.reset(token)
           response.headers["X-Request-ID"] = req_id
           return response

   • Expose this helper; consumers call add_request_id_middleware(app) once.

4. Integrate in app/main.py
   • Before creating the FastAPI app or as soon as possible, call configure_logging().
   • After app = FastAPI(...), call add_request_id_middleware(app).
   • Remove the old logging.basicConfig(...) call.
   • Ensure all existing log lines remain intact – the filter will enrich them automatically.

5. Compatibility
   • No other files should need changes.

Acceptance criteria

• uvicorn app.main:app starts without errors.
• Each HTTP response contains a header X-Request-ID whose value is a 32-char lowercase hex UUID.
• All log lines include the same request ID in square brackets for that request.
• Access log line format example:
  2025-07-08 12:34:56,789 [INFO] [d68a9d02c4c5493594f9654a4b8ac0fe] app.access: GET /health 200 (3 ms)
• Unit tests will be added in a follow-up issue.

Notes

This issue introduces a new file and modifies only app/main.py, minimizing conflict risk.