diff --git a/src/app/api/chat/route.ts b/src/app/api/chat/route.ts
index 606f070..d749cb7 100644
--- a/src/app/api/chat/route.ts
+++ b/src/app/api/chat/route.ts
@@ -17,11 +17,78 @@ import {
   getCustomOpenaiModelName,
 } from '@/lib/config';
 import { searchHandlers } from '@/lib/search';
-import { ChatApiBody as Body, Message, safeValidateBody } from './validation';
+import { z } from 'zod';
 
 export const runtime = 'nodejs';
 export const dynamic = 'force-dynamic';
 
+// Message schema
+const messageSchema = z.object({
+  messageId: z.string().min(1, 'Message ID is required'),
+  chatId: z.string().min(1, 'Chat ID is required'),
+  content: z.string().min(1, 'Message content is required'),
+});
+
+// ChatModel schema
+const chatModelSchema = z.object({
+  provider: z.string().optional(),
+  name: z.string().optional(),
+});
+
+// EmbeddingModel schema
+const embeddingModelSchema = z.object({
+  provider: z.string().optional(),
+  name: z.string().optional(),
+});
+
+// Main Body schema
+const bodySchema = z.object({
+  message: messageSchema,
+  optimizationMode: z.enum(['speed', 'balanced', 'quality'], {
+    errorMap: () => ({
+      message: 'Optimization mode must be one of: speed, balanced, quality',
+    }),
+  }),
+  focusMode: z.string().min(1, 'Focus mode is required'),
+  history: z
+    .array(
+      z.tuple([z.string(), z.string()], {
+        errorMap: () => ({
+          message: 'History items must be tuples of two strings',
+        }),
+      }),
+    )
+    .optional()
+    .default([]),
+  files: z.array(z.string()).optional().default([]),
+  chatModel: chatModelSchema.optional().default({}),
+  embeddingModel: embeddingModelSchema.optional().default({}),
+  systemInstructions: z.string().nullable().optional().default(''),
+});
+
+type Message = z.infer<typeof messageSchema>;
+type Body = z.infer<typeof bodySchema>;
+
+// Safe validation that returns success/error
+function safeValidateBody(data: unknown) {
+  const result = bodySchema.safeParse(data);
+
+  if (!result.success) {
+    return {
+      success: false,
+      error: result.error.errors.map((e) => ({
+        path: e.path.join('.'),
+        message: e.message,
+      })),
+    };
+  }
+
+  return {
+    success: true,
+    data: result.data,
+  };
+}
+
 const handleEmitterEvents = async (
   stream: EventEmitter,
   writer: WritableStreamDefaultWriter,
@@ -267,7 +334,7 @@ export const POST = async (req: Request) => {
       embedding,
       body.optimizationMode,
       body.files,
-      body.systemInstructions,
+      body.systemInstructions as string,
     );
 
     const responseStream = new TransformStream();
diff --git a/src/app/api/chat/validation.ts b/src/app/api/chat/validation.ts
deleted file mode 100644
index 8bed73f..0000000
--- a/src/app/api/chat/validation.ts
+++ /dev/null
@@ -1,70 +0,0 @@
-import { z } from 'zod';
-
-// Message schema
-const messageSchema = z.object({
-  messageId: z.string().min(1, 'Message ID is required'),
-  chatId: z.string().min(1, 'Chat ID is required'),
-  content: z.string().min(1, 'Message content is required'),
-});
-
-// ChatModel schema
-const chatModelSchema = z.object({
-  provider: z.string().optional(),
-  name: z.string().optional(),
-});
-
-// EmbeddingModel schema
-const embeddingModelSchema = z.object({
-  provider: z.string().optional(),
-  name: z.string().optional(),
-});
-
-// Main Body schema
-export const bodySchema = z.object({
-  message: messageSchema,
-  optimizationMode: z.enum(['speed', 'balanced', 'quality'], {
-    errorMap: () => ({
-      message: 'Optimization mode must be one of: speed, balanced, quality',
-    }),
-  }),
-  focusMode: z.string().min(1, 'Focus mode is required'),
-  history: z
-    .array(
-      z.tuple([z.string(), z.string()], {
-        errorMap: () => ({
-          message: 'History items must be tuples of two strings',
-        }),
-      }),
-    )
-    .optional()
-    .default([]),
-  files: z.array(z.string()).optional().default([]),
-  chatModel: chatModelSchema.optional().default({}),
-  embeddingModel: embeddingModelSchema.optional().default({}),
-  systemInstructions: z.string().optional().default(''),
-});
-
-export type Message = z.infer<typeof messageSchema>;
-export type ChatModel = z.infer<typeof chatModelSchema>;
-export type EmbeddingModel = z.infer<typeof embeddingModelSchema>;
-export type ChatApiBody = z.infer<typeof bodySchema>;
-
-// Safe validation that returns success/error
-export function safeValidateBody(data: unknown) {
-  const result = bodySchema.safeParse(data);
-
-  if (!result.success) {
-    return {
-      success: false,
-      error: result.error.errors.map((e) => ({
-        path: e.path.join('.'),
-        message: e.message,
-      })),
-    };
-  }
-
-  return {
-    success: true,
-    data: result.data,
-  };
-}