feat: support guest session (#919)

lib/ai/entitlements.ts

@@ -0,0 +1,29 @@
+import type { UserType } from '@/app/(auth)/auth';
+import type { ChatModel } from './models';
+
+interface Entitlements {
+  maxMessagesPerDay: number;
+  availableChatModelIds: Array<ChatModel['id']>;
+}
+
+export const entitlementsByUserType: Record<UserType, Entitlements> = {
+  /*
+   * For users without an account
+   */
+  guest: {
+    maxMessagesPerDay: 20,
+    availableChatModelIds: ['chat-model', 'chat-model-reasoning'],
+  },
+
+  /*
+   * For users with an account
+   */
+  regular: {
+    maxMessagesPerDay: 100,
+    availableChatModelIds: ['chat-model', 'chat-model-reasoning'],
+  },
+
+  /*
+   * TODO: For users with an account and a paid membership
+   */
+};