Update copilot-instructions.md

.github/copilot-instructions.md

@@ -33,6 +33,10 @@ This monorepo contains a Django backend and a Vite/React frontend, orchestrated
   - Static/media files: S3 in production, local in dev (see `settings.py`).
   - API versioning and docs: DRF Spectacular config in `settings.py`.
   - Custom permissions, filters, and serializers in each app.
+  - **Serializer Best Practices**:
+    - **Prevent Duplicate Schemas**: When the same `ChoiceField` or complex field appears in multiple serializers, define it once as a reusable field class and use it everywhere instead of repeated definitions.
+    - Example: Create `OrderStatusField(serializers.ChoiceField)` with `choices=Order.OrderStatus.choices` and reuse it in all serializers that need order status.
+    - This ensures consistent OpenAPI schema generation and reduces maintenance overhead.
 - **Frontend**
   - Use React Router layouts for shared UI (see `src/layouts/`, `LAYOUTS.md`).
   - API calls and JWT handling in `src/api/`.