fix auth

www/app/lib/useUserId.ts

@@ -0,0 +1,19 @@
+"use client";
+
+import { useState, useEffect } from "react";
+import { useSession as useNextAuthSession } from "next-auth/react";
+import { Session } from "next-auth";
+import { useAuth } from "./AuthProvider";
+
+const assertUserId = <T>(u: T): T & { id: string } => {
+  if (typeof (u as { id: string }).id !== "string")
+    throw new Error("Expected user.id to be a string");
+  return u as T & { id: string };
+};
+
+// the current assumption in useSessionUser is that "useNextAuthSession" also returns user.id, although useNextAuthSession documentation states it doesn't
+// the hook is to isolate the potential impact and to document this behaviour
+export default function useUserId() {
+  const auth = useAuth();
+  return auth.status === "authenticated" ? assertUserId(auth.user) : null;
+}