feat(observability): add phase9 health, readiness, metrics, request tracing, and simulator ops checks

Backend/middleware/observability.ts

@@ -0,0 +1,31 @@
+import { randomUUID } from 'crypto';
+
+import type { NextFunction, Request, Response } from 'express';
+
+import { incrementMetric } from '../observability/metrics';
+
+export const requestContext = (req: Request, res: Response, next: NextFunction): void => {
+  const requestId = req.headers['x-request-id']?.toString() ?? randomUUID();
+  const start = Date.now();
+
+  res.setHeader('x-request-id', requestId);
+  incrementMetric('http.requests.total');
+
+  res.on('finish', () => {
+    const durationMs = Date.now() - start;
+    incrementMetric(`http.status.${res.statusCode}`);
+
+    console.log(
+      JSON.stringify({
+        requestId,
+        method: req.method,
+        path: req.path,
+        statusCode: res.statusCode,
+        durationMs,
+        ip: req.ip,
+      }),
+    );
+  });
+
+  next();
+};