task-183: task.duration 耗时指标契约（Timer，非负、分模块、名称冻结）+ 8 条测试

backend-java/src/test/java/com/nanri/aiimage/metrics/TaskDurationMetricsTest.java

@@ -0,0 +1,77 @@
+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.assertTrue;
+
+/**
+ * task-183：task.duration 耗时记录契约（spec 11 §1）。
+ * 开始→终态耗时以 Timer 记录（未配置注册表时降级 debug 日志）；非负；分 moduleType。
+ */
+class TaskDurationMetricsTest {
+
+    private final SimpleMeterRegistry registry = new SimpleMeterRegistry();
+    private final TaskObservabilityMetrics metrics = new TaskObservabilityMetrics("server-110", registry);
+
+    private io.micrometer.core.instrument.Timer timer(String moduleType) {
+        return registry.get("aiimage.task.duration").tag("moduleType", moduleType).timer();
+    }
+
+    @Test
+    void durationRecorded() {
+        metrics.taskDuration("similarasin", 1_234L);
+        assertEquals(1, timer("similarasin").count());
+        assertEquals(1_234.0, timer("similarasin").totalTime(java.util.concurrent.TimeUnit.MILLISECONDS), 0.001);
+    }
+
+    @Test
+    void durationAccumulates() {
+        metrics.taskDuration("similarasin", 100L);
+        metrics.taskDuration("similarasin", 200L);
+        assertEquals(2, timer("similarasin").count());
+        assertEquals(300.0, timer("similarasin").totalTime(java.util.concurrent.TimeUnit.MILLISECONDS), 0.001);
+    }
+
+    @Test
+    void shortTaskRecorded() {
+        metrics.taskDuration("similarasin", 1L);
+        assertTrue(timer("similarasin").count() >= 1);
+    }
+
+    @Test
+    void longTaskRecordedLarger() {
+        metrics.taskDuration("similarasin", 600_000L);
+        assertEquals(600_000.0, timer("similarasin").totalTime(java.util.concurrent.TimeUnit.MILLISECONDS), 0.001);
+    }
+
+    @Test
+    void durationNeverNegative() {
+        metrics.taskDuration("similarasin", -5L);
+        assertEquals(0.0, timer("similarasin").totalTime(java.util.concurrent.TimeUnit.MILLISECONDS), 0.001,
+                "负耗时按 0 处理，不应破坏指标");
+    }
+
+    @Test
+    void durationSplitByModule() {
+        metrics.taskDuration("similarasin", 100L);
+        metrics.taskDuration("publish", 50L);
+        assertEquals(1, timer("similarasin").count());
+        assertEquals(1, timer("publish").count());
+    }
+
+    @Test
+    void durationNameFrozen() {
+        metrics.taskDuration("similarasin", 10L);
+        assertTrue(registry.getMeters().stream()
+                .anyMatch(m -> m.getId().getName().equals("aiimage.task.duration")));
+    }
+
+    @Test
+    void durationCarriesInstanceLabel() {
+        metrics.taskDuration("similarasin", 10L);
+        assertEquals("server-110",
+                registry.get("aiimage.task.duration").timer().getId().getTag("instanceId"));
+    }
+}