fix: fix worker's push_handler non-blocking error upon stop word (#5157)

lib/runtime/src/pipeline/network/ingress/push_handler.rs

@@ -282,9 +282,24 @@ where
                 m.response_bytes.inc_by(resp_bytes.len() as u64);
             }
             if (publisher.send(resp_bytes.into()).await).is_err() {
+                send_complete_final = false;
+                if context.is_stopped() {
+                    // Say there are 2 threads accessing `context`, the sequence can be either:
+                    // 1. context.stop_generating (other) -> publisher.send failure (this)
+                    //    -> context.is_stopped (this)
+                    // 2. publisher.send failure (this) -> context.stop_generating (other)
+                    //    -> context.is_stopped (this)
+                    // Case 1 can happen when client closed the connection after receiving the
+                    // complete response from frontend. Hence, send failure can be expected in this
+                    // case.
+                    tracing::warn!("Failed to publish response for stream {}", context.id());
+                } else {
+                    // Otherwise, this is an error.
                     tracing::error!("Failed to publish response for stream {}", context.id());
                     context.stop_generating();
-                send_complete_final = false;
+                }
+                // Account errors in all cases, including cancellation. Therefore this metric can be
+                // inflated.
                 if let Some(m) = self.metrics() {
                     m.error_counter
                         .with_label_values(&[work_handler::error_types::PUBLISH_RESPONSE])