fix(analytics): wrap GA4 fetch in waitUntil to prevent dropped events (#59)

The fire-and-forget fetch() in trackEvent() returns a dangling Promise
that the Vercel serverless runtime cancels the moment the response is
returned. With GA4_MEASUREMENT_ID and GA4_API_SECRET correctly set in
production, events were still never reaching google-analytics.com
because the POST was cut off mid-flight.

Wrap the fetch in waitUntil() from @vercel/functions so the runtime
keeps the function instance alive until the GA4 request settles —
without blocking the airdrop response.

waitUntil is runtime-agnostic and reads a context object Vercel
injects on globalThis; it does not change the deploy type, the runtime
(Node.js Fluid Compute), regions, or pricing. Outside Vercel it
silently no-ops, matching the prior fire-and-forget semantics.

Author: askov

lib/analytics.ts

@@ -10,6 +10,8 @@
  *   GA4_API_SECRET      – created in GA4 Admin › Data Streams › Measurement Protocol API secrets
  */
 
+import { waitUntil } from "@vercel/functions";
+
 const GA4_ENDPOINT = "https://www.google-analytics.com/mp/collect";
 
 type EventParams = Record<string, string | number | boolean | undefined>;
@@ -41,14 +43,16 @@ export function trackEvent(
     if (v !== undefined) cleanParams[k] = v;
   }
 
-  fetch(url, {
-    method: "POST",
-    headers: { "Content-Type": "application/json" },
-    body: JSON.stringify({
-      client_id: clientId,
-      events: [{ name, params: cleanParams }],
+  waitUntil(
+    fetch(url, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({
+        client_id: clientId,
+        events: [{ name, params: cleanParams }],
+      }),
+    }).catch((err) => {
+      console.error(`[ANALYTICS] Failed to send event "${name}":`, err);
     }),
-  }).catch((err) => {
-    console.error(`[ANALYTICS] Failed to send event "${name}":`, err);
-  });
+  );
 }

package-lock.json

@@ -21,6 +21,7 @@
     "@types/react": "18.2.14",
     "@types/react-dom": "18.2.6",
     "@vercel/edge-config": "^0.2.1",
+    "@vercel/functions": "^3.6.0",
     "autoprefixer": "10.4.14",
     "class-variance-authority": "^0.7.0",
     "eslint": "8.44.0",