diff --git a/scripts/backfill/__tests__/migrateRoom.test.ts b/scripts/backfill/__tests__/migrateRoom.test.ts
index 7ee86fdb8..40bd58eac 100644
--- a/scripts/backfill/__tests__/migrateRoom.test.ts
+++ b/scripts/backfill/__tests__/migrateRoom.test.ts
@@ -80,8 +80,15 @@ describe("migrateRoom", () => {
     expect(insertChat).toHaveBeenCalledTimes(1);
     // one batch call containing only the well-formed message
     expect(upsertChatMessages).toHaveBeenCalledTimes(1);
+    // `parts` stores the full UIMessage (matching the workflow's native
+    // persist path), not the bare parts array.
     expect(upsertChatMessages).toHaveBeenCalledWith([
-      expect.objectContaining({ id: "m1", chat_id: "room-1", role: "user" }),
+      expect.objectContaining({
+        id: "m1",
+        chat_id: "room-1",
+        role: "user",
+        parts: { id: "m1", role: "user", parts: [{ type: "text", text: "hi" }] },
+      }),
     ]);
     expect(stats.messagesWritten).toBe(1);
     expect(stats.messagesMalformed).toBe(1);
diff --git a/scripts/backfill/migrateRoom.ts b/scripts/backfill/migrateRoom.ts
index c95209ec2..79f8c192f 100644
--- a/scripts/backfill/migrateRoom.ts
+++ b/scripts/backfill/migrateRoom.ts
@@ -57,11 +57,16 @@ async function migrateMessages(
       malformed++;
       continue;
     }
+    // The workflow persists the FULL UIMessage in the `parts` column
+    // (see lib/chat/persistLatestUserMessage / persistAssistantMessage),
+    // and the read path (getSessionChatHandler) returns `parts` verbatim
+    // expecting a UIMessage. Store the same shape so migrated history
+    // deserializes identically to natively-written chats.
     rows.push({
       id: memory.id,
       chat_id: roomId,
       role: content.role,
-      parts: content.parts,
+      parts: { id: memory.id, role: content.role, parts: content.parts },
       created_at: memory.updated_at,
     });
   }