diff --git a/packages/backend/server/src/plugins/copilot/prompt.ts b/packages/backend/server/src/plugins/copilot/prompt.ts
index f7ab278e77..c71c4fc2fd 100644
--- a/packages/backend/server/src/plugins/copilot/prompt.ts
+++ b/packages/backend/server/src/plugins/copilot/prompt.ts
@@ -188,6 +188,7 @@ export class PromptService {
             create: messages.map((m, idx) => ({
               idx,
               ...m,
+              attachments: m.attachments || undefined,
               params: m.params || undefined,
             })),
           },
@@ -206,6 +207,7 @@ export class PromptService {
           create: messages.map((m, idx) => ({
             idx,
             ...m,
+            attachments: m.attachments || undefined,
             params: m.params || undefined,
           })),
         },
diff --git a/packages/backend/server/src/plugins/copilot/session.ts b/packages/backend/server/src/plugins/copilot/session.ts
index 607772d647..aa5b033a3c 100644
--- a/packages/backend/server/src/plugins/copilot/session.ts
+++ b/packages/backend/server/src/plugins/copilot/session.ts
@@ -161,6 +161,7 @@ export class ChatSessionService {
 
       const messages = state.messages.map(m => ({
         ...m,
+        attachments: m.attachments || undefined,
         params: m.params || undefined,
       }));
 
@@ -322,6 +323,7 @@ export class ChatSessionService {
             select: {
               role: true,
               content: true,
+              attachments: true,
               params: true,
               createdAt: true,
             },
diff --git a/packages/backend/server/src/plugins/copilot/types.ts b/packages/backend/server/src/plugins/copilot/types.ts
index 2d6f5651c1..805f0b3387 100644
--- a/packages/backend/server/src/plugins/copilot/types.ts
+++ b/packages/backend/server/src/plugins/copilot/types.ts
@@ -59,7 +59,7 @@ export const ChatMessageRole = Object.values(AiPromptRole) as [
 
 const PureMessageSchema = z.object({
   content: z.string(),
-  attachments: z.array(z.string()).optional(),
+  attachments: z.array(z.string()).optional().nullable(),
   params: z
     .record(z.union([z.string(), z.array(z.string())]))
     .optional()