fix: guard persist_order_line_output against cancelled lines

Completed renders no longer overwrite a cancelled status — a Blender job
that finishes after a cancel is issued is now silently dropped instead of
flipping the line back to completed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/domains/rendering/workflow_runtime_services.py

@@ -1229,6 +1229,8 @@ def persist_order_line_output(
     workflow_run_id: str | None = None,
 ) -> OutputSaveResult:
     """Persist the render result for an order line and publish the media asset if needed."""
+    if line.render_status == "cancelled":
+        return OutputSaveResult(status="failed", result_path=None)
     status: Literal["completed", "failed"] = "completed" if success else "failed"
     completed_at = render_completed_at or _utcnow_naive()
     persisted_output_path = output_path
@@ -1346,6 +1348,7 @@ def prepare_order_line_render_context(
     *,
     emit: EmitFn = None,
     persist_state: bool = True,
+    allow_completed_order_rerender: bool = False,
 ) -> OrderLineRenderSetupResult:
     """Load and validate the order line, then prepare reusable render inputs."""
     _emit(emit, order_line_id, "Loading order line from database")
@@ -1375,7 +1378,27 @@ def prepare_order_line_render_context(
     order = session.execute(
         select(Order).where(Order.id == line.order_id)
     ).scalar_one_or_none()
-    if order and order.status in (OrderStatus.rejected, OrderStatus.completed):
+    if order and order.status == OrderStatus.rejected:
+        _emit(emit, order_line_id, f"Order {order.status.value} — skipping render")
+        logger.info("OrderLine %s: order %s — skipping", order_line_id, order.status.value)
+        if persist_state and line.render_status in ("pending", "processing"):
+            session.execute(
+                sql_update(OrderLine)
+                .where(OrderLine.id == line.id)
+                .values(render_status="cancelled")
+            )
+            session.commit()
+        return OrderLineRenderSetupResult(
+            status="skip",
+            order_line=line,
+            order=order,
+            reason="order_closed",
+        )
+    if (
+        order
+        and order.status == OrderStatus.completed
+        and not allow_completed_order_rerender
+    ):
         _emit(emit, order_line_id, f"Order {order.status.value} — skipping render")
         logger.info("OrderLine %s: order %s — skipping", order_line_id, order.status.value)
         if persist_state and line.render_status in ("pending", "processing"):