fix(aiot): 告警触发时不发送持续时长，等待回岗后再计算

修改算法层告警触发逻辑：
- 移除 duration_minutes 字段（告警触发时不计算持续时长）
- 新增 first_frame_time 字段（记录离开时间）
- 修改消息为固定文本"人员离岗告警"

持续时长改为在人员回岗时由 alarm_resolve 事件计算

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

algorithms.py

@@ -289,16 +289,14 @@ class LeavePostAlgorithm:
                    (current_time - self.alert_cooldowns[cooldown_key]).total_seconds() > self.cooldown_sec:
 
                     bbox = self._get_latest_bbox(tracks, roi_id)
-                    total_off_duty_sec = (current_time - self._leave_start_time).total_seconds()
-                    elapsed_minutes = int(total_off_duty_sec / 60)
 
                     alerts.append({
                         "track_id": roi_id,
                         "camera_id": camera_id,
                         "bbox": bbox,
-                        "duration_minutes": elapsed_minutes,
                         "alert_type": "leave_post",
-                        "message": f"离岗 {elapsed_minutes} 分钟",
+                        "message": "人员离岗告警",
+                        "first_frame_time": self._leave_start_time.strftime('%Y-%m-%d %H:%M:%S'),
                     })
 
                     self.alert_cooldowns[cooldown_key] = current_time

test_leave_post_no_duration.py

@@ -0,0 +1,62 @@
+import sys
+sys.path.insert(0, 'C:/Users/16337/PycharmProjects/ai_edge')
+
+from algorithms import LeavePostAlgorithm
+from datetime import datetime, timedelta
+
+def test_alarm_trigger_no_duration():
+    """测试告警触发时不包含持续时长"""
+    algo = LeavePostAlgorithm(
+        confirm_on_duty_sec=1,
+        confirm_off_duty_sec=1,
+        leave_countdown_sec=2,
+    )
+
+    # 滑动窗口大小是10秒，我们需要在整个流程中考虑这一点
+    t0 = datetime(2026, 2, 12, 14, 0, 0)
+    person_track = [{"matched_rois": [{"roi_id": "roi1"}], "class": "person"}]
+
+    # 1. 上岗阶段：持续检测到人 (2秒，超过confirm_on_duty_sec=1秒)
+    for i in range(20):  # 每100ms一帧，共2秒
+        t = t0 + timedelta(milliseconds=i*100)
+        algo.process("roi1", "cam1", person_track, t)
+
+    print(f"[1] 上岗后状态: {algo.state}")
+    assert algo.state == "ON_DUTY", f"Expected ON_DUTY, got {algo.state}"
+
+    # 2. 离开阶段：等待11秒让窗口内的人检测完全过期，然后再发空帧
+    # 关键：需要等待窗口过期(10秒) + 确认时间(1秒)
+    t_leave_start = t0 + timedelta(seconds=2)
+
+    # 发送空帧超过窗口大小，确保detection_ratio变为0
+    for i in range(120):  # 每100ms一帧，共12秒
+        t = t_leave_start + timedelta(milliseconds=i*100)
+        algo.process("roi1", "cam1", [], t)
+
+    print(f"[2] 离开12秒后状态: {algo.state}")
+
+    # 3. 继续发送空帧，等待倒计时结束 (leave_countdown_sec=2秒)
+    t_wait_alarm = t_leave_start + timedelta(seconds=12)
+    for i in range(30):  # 每100ms一帧，共3秒 (超过倒计时)
+        t = t_wait_alarm + timedelta(milliseconds=i*100)
+        alerts = algo.process("roi1", "cam1", [], t)
+        if alerts:
+            break
+
+    print(f"[3] 告警触发后状态: {algo.state}")
+    print(f"   告警数量: {len(alerts)}")
+    print(f"   告警内容: {alerts}")
+
+    # ✅ 验证：告警不包含 duration_minutes
+    assert len(alerts) == 1, f"Expected 1 alert, got {len(alerts)}"
+    alarm = alerts[0]
+    assert alarm["alert_type"] == "leave_post"
+    assert "duration_minutes" not in alarm, "告警不应包含 duration_minutes"
+    assert "first_frame_time" in alarm, "告警应包含 first_frame_time"
+    assert alarm["message"] == "人员离岗告警", f"消息错误: {alarm['message']}"
+
+    print(f"测试通过：告警不含持续时长")
+    print(f"   first_frame_time: {alarm['first_frame_time']}")
+
+if __name__ == "__main__":
+    test_alarm_trigger_no_duration()