功能：新增会话记忆管理器，支持多轮对话状态机

每用户独立会话，10轮对话上限，10分钟TTL自动过期。
状态机：idle/waiting_location/waiting_confirm/waiting_close_photo

app/services/session_manager.py

@@ -0,0 +1,108 @@
+"""
+会话记忆管理器
+
+管理每个用户的对话上下文，支持多轮对话状态机。
+内存缓存，10 分钟 TTL 自动清除。
+"""
+
+import time
+from typing import Dict, List, Optional
+
+from app.utils.logger import logger
+
+SESSION_TTL = 600  # 10 分钟
+
+
+class UserSession:
+    """单个用户的会话上下文"""
+
+    def __init__(self, user_id: str):
+        self.user_id = user_id
+        self.state = "idle"  # idle / waiting_location / waiting_confirm / waiting_close_photo
+        self.pending_image_url = ""      # 暂存的图片 COS key
+        self.pending_analysis = ""       # VLM 分析结果描述
+        self.pending_alarm_type = ""     # VLM 识别的告警类型
+        self.pending_order_id = ""       # 待结单的工单 ID
+        self.pending_alarm_id = ""       # 关联的告警 ID
+        self.history: List[Dict] = []    # 对话历史 [{"role": "user/assistant", "content": ...}]
+        self.updated_at = time.time()
+
+    def is_expired(self) -> bool:
+        return time.time() - self.updated_at > SESSION_TTL
+
+    def touch(self):
+        self.updated_at = time.time()
+
+    def reset(self):
+        """重置状态机（保留 history）"""
+        self.state = "idle"
+        self.pending_image_url = ""
+        self.pending_analysis = ""
+        self.pending_alarm_type = ""
+        self.pending_order_id = ""
+        self.pending_alarm_id = ""
+
+    def add_history(self, role: str, content):
+        """添加对话记录，content 可以是 str 或 list（多模态）"""
+        self.history.append({"role": role, "content": content})
+        # 保留最近 10 轮（20 条消息）
+        if len(self.history) > 20:
+            self.history = self.history[-20:]
+        self.touch()
+
+    def get_history_for_vlm(self) -> List[Dict]:
+        """获取用于 VLM 调用的 history（过滤掉过大的图片内容）"""
+        return self.history.copy()
+
+
+class SessionManager:
+    """全局会话管理器（单例）"""
+
+    def __init__(self):
+        self._sessions: Dict[str, UserSession] = {}
+        self._last_cleanup = time.time()
+
+    def get(self, user_id: str) -> UserSession:
+        """获取或创建用户会话"""
+        # 定期清理过期会话（每 5 分钟）
+        if time.time() - self._last_cleanup > 300:
+            self._cleanup_expired()
+
+        session = self._sessions.get(user_id)
+        if session and not session.is_expired():
+            session.touch()
+            return session
+
+        # 过期或不存在，创建新会话
+        session = UserSession(user_id)
+        self._sessions[user_id] = session
+        return session
+
+    def clear(self, user_id: str):
+        """清除用户会话"""
+        if user_id in self._sessions:
+            self._sessions[user_id].reset()
+            self._sessions[user_id].history.clear()
+
+    def _cleanup_expired(self):
+        """清理过期会话"""
+        expired = [uid for uid, s in self._sessions.items() if s.is_expired()]
+        for uid in expired:
+            del self._sessions[uid]
+        if expired:
+            logger.debug(f"清理 {len(expired)} 个过期会话")
+        self._last_cleanup = time.time()
+
+    @property
+    def active_count(self) -> int:
+        return sum(1 for s in self._sessions.values() if not s.is_expired())
+
+
+_session_manager: Optional[SessionManager] = None
+
+
+def get_session_manager() -> SessionManager:
+    global _session_manager
+    if _session_manager is None:
+        _session_manager = SessionManager()
+    return _session_manager