feat: add runnable simulator foundation

app/api/middleware.py

@@ -0,0 +1,42 @@
+"""Request correlation and access logging middleware."""
+
+from __future__ import annotations
+
+import logging
+import time
+import uuid
+from collections.abc import Awaitable, Callable
+
+from fastapi import Request, Response
+from starlette.middleware.base import BaseHTTPMiddleware
+
+logger = logging.getLogger(__name__)
+
+RequestHandler = Callable[[Request], Awaitable[Response]]
+
+
+class RequestContextMiddleware(BaseHTTPMiddleware):
+    """Attach a bounded request ID and log one structured completion event."""
+
+    def __init__(self, app: object, header_name: str) -> None:
+        super().__init__(app)  # type: ignore[arg-type]
+        self._header_name = header_name
+
+    async def dispatch(self, request: Request, call_next: RequestHandler) -> Response:
+        supplied = request.headers.get(self._header_name, "")
+        request_id = supplied if 0 < len(supplied) <= 128 else str(uuid.uuid4())
+        request.state.request_id = request_id
+        started = time.monotonic()
+        response = await call_next(request)
+        response.headers[self._header_name] = request_id
+        logger.info(
+            "request completed",
+            extra={
+                "request_id": request_id,
+                "method": request.method,
+                "path": request.url.path,
+                "status": response.status_code,
+                "duration_ms": round((time.monotonic() - started) * 1000, 3),
+            },
+        )
+        return response