Delegate non-/ws/runs upgrade requests to Next instead of dropping them

Our upgrade handler on the shared httpServer was destroying every socket
that wasn't for /ws/runs, which silently killed Next's own dev-mode HMR
websocket (/_next/hmr) too - breaking hot reload with no useful error,
just a failed WebSocket connection in the browser console. Delegate to
app.getUpgradeHandler() instead, which must be called after prepare().

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/server.ts

@@ -23,6 +23,8 @@ const app = next({ dev, hostname, port });
 const handle = app.getRequestHandler();
 
 app.prepare().then(() => {
+  const nextUpgradeHandler = app.getUpgradeHandler();
+
   const httpServer = createServer((req, res) => {
     handle(req, res);
   });
@@ -33,7 +35,8 @@ app.prepare().then(() => {
   httpServer.on("upgrade", (req, socket, head) => {
     const { pathname } = new URL(req.url ?? "/", "http://internal");
     if (pathname !== "/ws/runs") {
-      socket.destroy();
+      // Anything else (e.g. Next's own dev-mode HMR websocket at /_next/hmr) is Next's to handle.
+      nextUpgradeHandler(req, socket, head).catch(() => socket.destroy());
       return;
     }