fix(vercel-analytics): sink insight POSTs in dev to avoid 404s

Vercel Analytics collects via a relative `/_vercel/insights/*` endpoint
served by Vercel's edge. Outside Vercel (including `nuxt dev`) there is
no upstream, so the script POSTs to the local origin and 404s.

Register a dev-only handler that returns 204 on that path when
vercelAnalytics is enabled. Script behaviour, options (mode/debug), and
proxy domains are unchanged.

Author: harlan-zw

packages/script/src/module.ts

@@ -527,6 +527,16 @@ export default defineNuxtModule<ModuleOptions>({
     const proxyHandlerPath = await resolvePath('./runtime/server/proxy-handler')
     addServerHandler({ route: `${proxyPrefix}/**`, handler: proxyHandlerPath })
 
+    // In dev, sink Vercel Analytics insight POSTs to `/_vercel/insights/*` so
+    // they don't 404. Vercel's edge serves this path in production; locally
+    // there's no upstream, so we return 204 to keep the script happy.
+    if (nuxt.options.dev && config.registry?.vercelAnalytics) {
+      addServerHandler({
+        route: '/_vercel/insights/**',
+        handler: await resolvePath('./runtime/server/vercel-insights-sink'),
+      })
+    }
+
     const composables = [
       'useScript',
       'useScriptEventPage',

packages/script/src/runtime/server/vercel-insights-sink.ts

@@ -0,0 +1,6 @@
+import { defineEventHandler, setResponseStatus } from 'h3'
+
+export default defineEventHandler((event) => {
+  setResponseStatus(event, 204)
+  return null
+})