diff --git a/backend-java/src/test/java/com/nanri/aiimage/metrics/TaskHeartbeatAgeMetricsTest.java b/backend-java/src/test/java/com/nanri/aiimage/metrics/TaskHeartbeatAgeMetricsTest.java
new file mode 100644
index 00000000..1615b720
--- /dev/null
+++ b/backend-java/src/test/java/com/nanri/aiimage/metrics/TaskHeartbeatAgeMetricsTest.java
@@ -0,0 +1,79 @@
+package com.nanri.aiimage.metrics;
+
+import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * task-184：task.heartbeat.age 心跳年龄 gauge 契约（spec 11 §1）。
+ * 年龄 = 距最后心跳的毫秒数，由 TaskHeartbeatService/巡检写入；新鲜/陈旧可观测；
+ * 刚心跳≈0；时钟负保护；未设置不产生 meter。
+ */
+class TaskHeartbeatAgeMetricsTest {
+
+    private final SimpleMeterRegistry registry = new SimpleMeterRegistry();
+    private final TaskObservabilityMetrics metrics = new TaskObservabilityMetrics("server-110", registry);
+
+    private io.micrometer.core.instrument.Gauge gauge(String moduleType) {
+        return registry.get("aiimage.task.heartbeat.age").tag("moduleType", moduleType).gauge();
+    }
+
+    @Test
+    void ageComputedFreshAndStale() {
+        metrics.taskHeartbeatAge("similarasin", 200L);
+        assertEquals(200.0, gauge("similarasin").value(), "新鲜心跳年龄应小");
+        metrics.taskHeartbeatAge("similarasin", 3_600_000L);
+        assertEquals(3_600_000.0, gauge("similarasin").value(), "陈旧心跳年龄应大");
+    }
+
+    @Test
+    void ageJustHeartbeatIsZero() {
+        metrics.taskHeartbeatAge("similarasin", 0L);
+        assertEquals(0.0, gauge("similarasin").value());
+    }
+
+    @Test
+    void ageClockNegativeGuard() {
+        metrics.taskHeartbeatAge("similarasin", -100L);
+        assertEquals(0.0, gauge("similarasin").value(), "时钟回拨导致的负年龄按 0 处理");
+    }
+
+    @Test
+    void ageUpdatesOnEachWrite() {
+        metrics.taskHeartbeatAge("similarasin", 1_000L);
+        metrics.taskHeartbeatAge("similarasin", 2_000L);
+        assertEquals(2_000.0, gauge("similarasin").value());
+    }
+
+    @Test
+    void ageSplitByModule() {
+        metrics.taskHeartbeatAge("similarasin", 500L);
+        metrics.taskHeartbeatAge("publish", 900L);
+        assertEquals(500.0, gauge("similarasin").value());
+        assertEquals(900.0, gauge("publish").value());
+    }
+
+    @Test
+    void noHeartbeatYetNoGauge() {
+        assertNull(registry.find("aiimage.task.heartbeat.age")
+                        .tag("moduleType", "withdraw").gauge(),
+                "从未写入心跳年龄时不应产生 gauge");
+    }
+
+    @Test
+    void ageNameFrozen() {
+        metrics.taskHeartbeatAge("similarasin", 10L);
+        assertTrue(registry.getMeters().stream()
+                .anyMatch(m -> m.getId().getName().equals("aiimage.task.heartbeat.age")));
+    }
+
+    @Test
+    void ageCarriesInstanceLabel() {
+        metrics.taskHeartbeatAge("similarasin", 10L);
+        assertEquals("server-110",
+                registry.get("aiimage.task.heartbeat.age").gauge().getId().getTag("instanceId"));
+    }
+}