fix: cache Convex JWT in server auth

lib/auth-server.ts

@@ -1,5 +1,30 @@
 import { convexBetterAuthNextJs } from "@convex-dev/better-auth/nextjs";
 
+function getErrorText(error: unknown): string {
+  if (error instanceof Error) {
+    return error.message;
+  }
+
+  if (typeof error === "string") {
+    return error;
+  }
+
+  if (error && typeof error === "object") {
+    const { data, message } = error as { data?: unknown; message?: unknown };
+    return [message, data]
+      .filter((value): value is string => typeof value === "string")
+      .join(" ");
+  }
+
+  return "";
+}
+
+function isConvexAuthError(error: unknown): boolean {
+  return /\b(Unauthenticated|Unauthorized|Not authenticated)\b/i.test(
+    getErrorText(error),
+  );
+}
+
 export const {
   handler,
   preloadAuthQuery,
@@ -11,4 +36,8 @@ export const {
 } = convexBetterAuthNextJs({
   convexUrl: process.env.NEXT_PUBLIC_CONVEX_URL!,
   convexSiteUrl: process.env.NEXT_PUBLIC_CONVEX_SITE_URL!,
+  jwtCache: {
+    enabled: true,
+    isAuthError: isConvexAuthError,
+  },
 });