diff --git a/backend-java/src/main/java/com/nanri/aiimage/common/exception/GlobalExceptionHandler.java b/backend-java/src/main/java/com/nanri/aiimage/common/exception/GlobalExceptionHandler.java
index 5ac6409e..06e7daa7 100644
--- a/backend-java/src/main/java/com/nanri/aiimage/common/exception/GlobalExceptionHandler.java
+++ b/backend-java/src/main/java/com/nanri/aiimage/common/exception/GlobalExceptionHandler.java
@@ -55,10 +55,19 @@ public class GlobalExceptionHandler {
                     ? ApiResponse.fail(forwardEx.getMessage())
                     : ApiResponse.fail(forwardEx.getCode(), forwardEx.getMessage());
         } catch (Exception forwardEx) {
+            // 转发失败是**瞬时基础设施故障**（归属实例正在滚动重启），不是业务结论，
+            // 更不能表达成「任务不存活」。原先返回 ApiResponse.fail(40903) —— HTTP 200
+            // 加 data:null，而客户端那句 bool((resp.json().get("data") or {}).get("alive"))
+            // 会把「拿不到数据」折叠成 alive=false，于是客户端把**健康的长任务主动停掉**：
+            // 2026-09-18 任务 28616 就是这么死的（归属节点 server-110 重启窗口内，心跳经
+            // nginx 落到 server-121，转发 3 次 Connection refused 后返回空 data）。
+            // 改为 503 + 空 body：新客户端按状态码判为「未知」继续跑；老客户端因 body 不是
+            // JSON、resp.json() 抛异常，同样落到「未知」。顺带让这类故障在 HTTP 指标里可见
+            // （原先记成 200，监控完全看不到滚动重启期间丢了多少心跳）。
             log.warn("[instance-routing] forward failed taskId={} operation={} owner={} current={} msg={}",
                     ex.getTaskId(), ex.getOperation(), ex.getOwnerInstanceId(), ex.getCurrentInstanceId(),
                     forwardEx.getMessage(), forwardEx);
-            return ApiResponse.fail(40903, "任务归属实例转发失败: " + forwardEx.getMessage());
+            return ResponseEntity.status(HttpStatus.SERVICE_UNAVAILABLE).build();
         }
     }
 
diff --git a/backend-java/src/test/java/com/nanri/aiimage/common/exception/GlobalExceptionHandlerTest.java b/backend-java/src/test/java/com/nanri/aiimage/common/exception/GlobalExceptionHandlerTest.java
new file mode 100644
index 00000000..96b40f51
--- /dev/null
+++ b/backend-java/src/test/java/com/nanri/aiimage/common/exception/GlobalExceptionHandlerTest.java
@@ -0,0 +1,85 @@
+package com.nanri.aiimage.common.exception;
+
+import com.nanri.aiimage.common.api.ApiResponse;
+import com.nanri.aiimage.common.service.TaskOwnerForwardService;
+import jakarta.servlet.http.HttpServletRequest;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.client.ResourceAccessException;
+
+import java.net.ConnectException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+/**
+ * 跨实例转发的失败语义。
+ *
+ * <p>2026-09-18 任务 28616：归属节点 server-110 滚动重启期间，客户端心跳经 nginx 落到
+ * server-121，转发 3 次 Connection refused。当时这里返回 {@code ApiResponse.fail(40903)}
+ * ——HTTP 200 + {@code data:null}，而客户端用
+ * {@code bool((resp.json().get("data") or {}).get("alive"))} 解析，把「拿不到数据」折叠成
+ * {@code alive=false}，于是客户端把一个跑到 66/253 的健康上架任务主动停掉、关闭店铺。
+ * 修复后转发失败返回 503 + 空 body：新客户端按状态码判为「未知」，老客户端因 body 不是
+ * JSON、解析抛异常同样落到「未知」，两边都不会再自杀。</p>
+ */
+@ExtendWith(MockitoExtension.class)
+class GlobalExceptionHandlerTest {
+
+    @Mock private TaskOwnerForwardService taskOwnerForwardService;
+
+    @InjectMocks private GlobalExceptionHandler handler;
+
+    private static TaskOwnerMismatchException ownerMismatch() {
+        return new TaskOwnerMismatchException(28616L, "PUBLISH task heartbeat", "server-110", "server-121");
+    }
+
+    @Test
+    void forwardConnectFailureReturns503WithEmptyBody() {
+        when(taskOwnerForwardService.forwardCurrentRequest(any(), any()))
+                .thenThrow(new ResourceAccessException("Connection refused",
+                        new ConnectException("Connection refused")));
+
+        Object result = handler.handleTaskOwnerMismatchException(ownerMismatch(), mock(HttpServletRequest.class));
+
+        ResponseEntity<?> response = assertInstanceOf(ResponseEntity.class, result);
+        assertEquals(HttpStatus.SERVICE_UNAVAILABLE, response.getStatusCode());
+        // 空 body 是关键：一旦带上 JSON，老客户端的 bool((data or {}).get("alive")) 又会判成「死」
+        assertNull(response.getBody(), "转发失败必须无响应体，否则老客户端会把未知当成任务已死");
+    }
+
+    @Test
+    void successfulForwardPassesThroughUpstreamStatusAndBody() {
+        byte[] upstream = "{\"success\":true,\"data\":{\"alive\":true}}".getBytes(java.nio.charset.StandardCharsets.UTF_8);
+        when(taskOwnerForwardService.forwardCurrentRequest(any(), any()))
+                .thenReturn(ResponseEntity.ok(upstream));
+
+        Object result = handler.handleTaskOwnerMismatchException(ownerMismatch(), mock(HttpServletRequest.class));
+
+        ResponseEntity<?> response = assertInstanceOf(ResponseEntity.class, result);
+        assertEquals(HttpStatus.OK, response.getStatusCode());
+        assertEquals(upstream, response.getBody(), "转发成功时上游响应体必须原样透传");
+    }
+
+    @Test
+    void configErrorKeepsBusinessEnvelopeInsteadOfServiceUnavailable() {
+        // 路由未配置 / 检测到转发循环属于配置错误，不是瞬时故障：保留业务信封，不回 503
+        when(taskOwnerForwardService.forwardCurrentRequest(any(), any()))
+                .thenThrow(new BusinessException(40903, "任务归属实例未配置服务路由：server-110"));
+
+        Object result = handler.handleTaskOwnerMismatchException(ownerMismatch(), mock(HttpServletRequest.class));
+
+        ApiResponse<?> response = assertInstanceOf(ApiResponse.class, result);
+        assertFalse(response.isSuccess(), "配置错误仍按业务失败返回");
+    }
+}