feat(aiot): 实现离岗倒计时功能 - 修复持续时长过短问题

问题描述：
- 用户反馈告警持续时长只有48秒、103秒
- 预期：离岗倒计时5分钟后才告警，持续时长应>5.5分钟
- 根因：代码在"离岗确认"后立即触发告警，缺少倒计时环节

业务流程：
1. 上岗确认期：10秒（confirm_on_duty_sec）
2. 离岗确认期：30秒（confirm_leave_sec）
3. 离岗倒计时：300秒（leave_countdown_sec）← 新增
4. 告警冷却期：600秒（cooldown_sec）

修改内容：
1. LeavePostAlgorithm 构造函数
   - 新增 leave_countdown_sec 参数（默认300秒）
   - 新增 _off_duty_start_time 状态变量
   - 新增 _alarm_triggered 告警标志

2. LEAVING → OFF_DUTY 状态转换（Line 197-207）
   - 移除立即告警逻辑
   - 进入OFF_DUTY后仅记录时间，开始倒计时

3. OFF_DUTY 状态处理（Line 209-258）
   - 新增倒计时检查：off_duty_elapsed >= leave_countdown_sec
   - 倒计时结束才触发告警
   - 人员回岗时检查是否已告警，决定是否发送resolve事件

4. 算法实例创建（Line 600-607, 701-708）
   - 从配置读取 leave_countdown_sec（默认300秒）

5. reset() 方法
   - 清理新增状态变量

影响范围：
- 告警时机：从离岗确认后立即告警 → 倒计时结束后告警
- 持续时长：现在必然 >= 330秒（30s确认 + 300s倒计时）

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

algorithms.py

@@ -28,12 +28,14 @@ class LeavePostAlgorithm:
         self,
         confirm_on_duty_sec: int = 10,
         confirm_leave_sec: int = 30,
+        leave_countdown_sec: int = 300,  # 新增：离岗倒计时（默认5分钟）
         cooldown_sec: int = 600,
         working_hours: Optional[List[Dict]] = None,
         target_class: Optional[str] = "person",
     ):
         self.confirm_on_duty_sec = confirm_on_duty_sec
         self.confirm_leave_sec = confirm_leave_sec
+        self.leave_countdown_sec = leave_countdown_sec  # 离岗倒计时
         self.cooldown_sec = cooldown_sec
         self.working_hours = working_hours or []
         self.target_class = target_class
@@ -48,6 +50,8 @@ class LeavePostAlgorithm:
         self.last_person_time: Optional[datetime] = None
 
         self._last_alarm_id: Optional[str] = None      # 最近一次告警ID
+        self._off_duty_start_time: Optional[datetime] = None  # OFF_DUTY状态开始时间（用于倒计时）
+        self._alarm_triggered: bool = False  # 是否已触发告警（OFF_DUTY期间只告警一次）
         self._leave_start_time: Optional[datetime] = None  # 离岗开始时间（LEAVING 状态的开始时间）
 
     def _is_in_working_hours(self, dt: Optional[datetime] = None) -> bool:
@@ -192,19 +196,53 @@ class LeavePostAlgorithm:
             elapsed = (current_time - self.state_start_time).total_seconds()
 
             if roi_has_person:
+                # 人回来了，回到ON_DUTY
                 self.state = self.STATE_ON_DUTY
                 self.state_start_time = current_time
             elif elapsed >= self.confirm_leave_sec:
-                # 确认离岗后直接触发告警，不再进入 OFF_DUTY 二次等待
+                # 离岗确认期结束 → 进入OFF_DUTY开始倒计时（暂不触发告警）
-                leaving_start_time = self.state_start_time  # 保存 LEAVING 状态开始时间（人员离开时间）
+                leaving_start_time = self.state_start_time  # 保存人员离开时间
                 self.state = self.STATE_OFF_DUTY
                 self.state_start_time = current_time
+                self._off_duty_start_time = current_time  # 记录OFF_DUTY开始时间用于倒计时
+                self._leave_start_time = leaving_start_time  # 保存LEAVING开始时间（人员离开时间）
+                self._alarm_triggered = False  # 重置告警标志
 
+        elif self.state == self.STATE_OFF_DUTY:
+            # OFF_DUTY 状态：离岗倒计时 + 等待人员回岗
+            off_duty_elapsed = (current_time - self._off_duty_start_time).total_seconds() if self._off_duty_start_time else 0
+
+            if roi_has_person:
+                # 人员回岗
+                if self._last_alarm_id and self._leave_start_time and self._alarm_triggered:
+                    # 如果已经触发过告警，发送resolve事件
+                    duration_ms = int((current_time - self._leave_start_time).total_seconds() * 1000)
+                    alerts.append({
+                        "alert_type": "alarm_resolve",
+                        "resolve_alarm_id": self._last_alarm_id,
+                        "duration_ms": duration_ms,
+                        "last_frame_time": current_time.strftime('%Y-%m-%d %H:%M:%S'),
+                        "resolve_type": "person_returned",
+                    })
+                # 清理告警追踪信息
+                self._last_alarm_id = None
+                self._leave_start_time = None
+                self._off_duty_start_time = None
+                self._alarm_triggered = False
+                # 回到确认在岗状态
+                self.state = self.STATE_CONFIRMING
+                self.state_start_time = current_time
+                self.detection_history.clear()
+                self.detection_history.append((current_time, True))
+            elif off_duty_elapsed >= self.leave_countdown_sec and not self._alarm_triggered:
+                # 离岗倒计时结束，触发告警
                 cooldown_key = f"{camera_id}_{roi_id}"
                 now = datetime.now()
                 if cooldown_key not in self.alert_cooldowns or (now - self.alert_cooldowns[cooldown_key]).total_seconds() > self.cooldown_sec:
                     bbox = self._get_latest_bbox(tracks, roi_id)
-                    elapsed_minutes = int(elapsed / 60)
+                    # 计算总离岗时长（从人离开到现在）
+                    total_leave_duration = (current_time - self._leave_start_time).total_seconds() if self._leave_start_time else 0
+                    elapsed_minutes = int(total_leave_duration / 60)
                     alerts.append({
                         "track_id": roi_id,
                         "camera_id": camera_id,
@@ -214,31 +252,8 @@ class LeavePostAlgorithm:
                         "message": f"离岗 {elapsed_minutes} 分钟",
                     })
                     self.alert_cooldowns[cooldown_key] = now
-
+                    self._alarm_triggered = True  # 标记已触发告警
-                    # 保存告警追踪信息（alarm_id 由 main.py 通过 set_last_alarm_id() 回填）
+                    # alarm_id 由 main.py 通过 set_last_alarm_id() 回填
-                    self._last_alarm_id = None
-                    self._leave_start_time = leaving_start_time  # LEAVING 状态开始时间 = 人员离开时间
-
-        elif self.state == self.STATE_OFF_DUTY:
-            # OFF_DUTY 状态：只等待人员回岗，不再重复告警
-            # 必须经过 CONFIRMING 重新确认在岗后，才允许新一轮离岗检测
-            if roi_has_person:
-                # 生成 resolve 事件（人员回岗）
-                if self._last_alarm_id and self._leave_start_time:
-                    duration_ms = int((current_time - self._leave_start_time).total_seconds() * 1000)
-                    alerts.append({
-                        "alert_type": "alarm_resolve",
-                        "resolve_alarm_id": self._last_alarm_id,
-                        "duration_ms": duration_ms,
-                        "last_frame_time": current_time.strftime('%Y-%m-%d %H:%M:%S'),
-                        "resolve_type": "person_returned",
-                    })
-                self._last_alarm_id = None
-                self._leave_start_time = None
-                self.state = self.STATE_CONFIRMING
-                self.state_start_time = current_time
-                self.detection_history.clear()
-                self.detection_history.append((current_time, True))
 
         return alerts
 
@@ -255,6 +270,8 @@ class LeavePostAlgorithm:
         self.alert_cooldowns.clear()
         self._last_alarm_id = None
         self._leave_start_time = None
+        self._off_duty_start_time = None
+        self._alarm_triggered = False
 
     def get_state(self, roi_id: str) -> Dict[str, Any]:
         return {
@@ -583,6 +600,7 @@ class AlgorithmManager:
                         self.algorithms[roi_id][key]["leave_post"] = LeavePostAlgorithm(
                             confirm_on_duty_sec=algo_params["confirm_on_duty_sec"],
                             confirm_leave_sec=algo_params["confirm_leave_sec"],
+                            leave_countdown_sec=algo_params.get("leave_countdown_sec", 300),  # 离岗倒计时，默认5分钟
                             cooldown_sec=algo_params["cooldown_sec"],
                             working_hours=algo_params["working_hours"],
                             target_class=algo_params["target_class"],
@@ -683,6 +701,7 @@ class AlgorithmManager:
             self.algorithms[roi_id][key]["leave_post"] = LeavePostAlgorithm(
                 confirm_on_duty_sec=algo_params.get("confirm_on_duty_sec", 10),
                 confirm_leave_sec=algo_params.get("confirm_leave_sec", 30),
+                leave_countdown_sec=algo_params.get("leave_countdown_sec", 300),  # 离岗倒计时，默认5分钟
                 cooldown_sec=algo_params.get("cooldown_sec", 600),
                 working_hours=roi_working_hours,
                 target_class=algo_params.get("target_class", "person"),