[claude] API observability — structured logging + /api/metrics endpoint (#57) (#87)

artifacts/api-server/src/middlewares/request-id.ts

@@ -0,0 +1,18 @@
+import crypto from "crypto";
+import type { Request, Response, NextFunction } from "express";
+
+const HEADER = "X-Request-Id";
+
+/**
+ * Assigns a unique request ID to every incoming request.
+ * If the client (or a reverse proxy) already sent X-Request-Id, reuse it;
+ * otherwise generate a short random hex string.
+ * The ID is stored on `res.locals.requestId` for downstream middleware/routes
+ * and echoed back via the X-Request-Id response header.
+ */
+export function requestIdMiddleware(req: Request, res: Response, next: NextFunction): void {
+  const id = (req.headers[HEADER.toLowerCase()] as string | undefined) ?? crypto.randomUUID();
+  res.locals["requestId"] = id;
+  res.setHeader(HEADER, id);
+  next();
+}