feat: only send user message as part of request (#957)

app/(chat)/api/chat/schema.ts

@@ -0,0 +1,29 @@
+import { z } from 'zod';
+
+const textPartSchema = z.object({
+  text: z.string().min(1).max(2000),
+  type: z.enum(['text']),
+});
+
+export const postRequestBodySchema = z.object({
+  id: z.string().uuid(),
+  message: z.object({
+    id: z.string().uuid(),
+    createdAt: z.coerce.date(),
+    role: z.enum(['user']),
+    content: z.string().min(1).max(2000),
+    parts: z.array(textPartSchema),
+    experimental_attachments: z
+      .array(
+        z.object({
+          url: z.string().url(),
+          name: z.string().min(1).max(2000),
+          contentType: z.enum(['image/png', 'image/jpg', 'image/jpeg']),
+        }),
+      )
+      .optional(),
+  }),
+  selectedChatModel: z.enum(['chat-model', 'chat-model-reasoning']),
+});
+
+export type PostRequestBody = z.infer<typeof postRequestBodySchema>;