feat(models): 组织、用户、角色、客户、会话与消息模型

按组织边界定义数据关系，补齐仓储层与通用工具，迁移脚本可重复执行。

backend/app/models/session_to_agent.py

@@ -0,0 +1,109 @@
+"""
+Copyright 2024-2026 ReplyPier
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+from sqlalchemy import Column, String, DateTime, ForeignKey, Enum as SQLEnum, JSON, Float
+from sqlalchemy.orm import relationship
+from sqlalchemy.dialects.postgresql import UUID
+from app.core.encryption import EncryptedText
+from app.database import Base
+import enum
+from sqlalchemy.sql import func
+from app.models.user import UserGroup
+
+
+class SessionStatus(str, enum.Enum):
+    OPEN = "open"
+    TRANSFERRED = "transferred"
+    CLOSED  = "closed"
+
+
+class EndChatReasonType(str, enum.Enum):
+    ISSUE_RESOLVED = "ISSUE_RESOLVED"
+    CUSTOMER_REQUEST = "CUSTOMER_REQUEST"
+    CONFIRMATION_RECEIVED = "CONFIRMATION_RECEIVED"
+    FAREWELL = "FAREWELL"
+    THANK_YOU = "THANK_YOU"
+    NATURAL_CONCLUSION = "NATURAL_CONCLUSION"
+    TASK_COMPLETED = "TASK_COMPLETED"
+
+
+# A conversation the visitor can still talk in.
+ACTIVE_STATUSES = (SessionStatus.OPEN, SessionStatus.TRANSFERRED)
+
+
+class SessionToAgent(Base):
+    __tablename__ = "session_to_agents"
+
+    session_id = Column(UUID(as_uuid=True), primary_key=True)
+    user_id = Column(UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True)
+    agent_id = Column(UUID(as_uuid=True), ForeignKey("agents.id", ondelete="SET NULL"), nullable=True)
+    customer_id = Column(UUID(as_uuid=True), ForeignKey("customers.id", ondelete="SET NULL"), nullable=False, index=True)
+    group_id = Column(UUID(as_uuid=True), ForeignKey("groups.id", ondelete="SET NULL"), nullable=True)
+    organization_id = Column(UUID(as_uuid=True), ForeignKey("organizations.id", ondelete="CASCADE"), nullable=False)
+    status = Column(SQLEnum(SessionStatus), nullable=False, default=SessionStatus.OPEN)
+    # Messaging channel the session belongs to ('web' = widget, 'telegram',
+    # 'whatsapp', ...). Routing key for outbound delivery of replies.
+    channel = Column(String, nullable=False, server_default='web', index=True)
+    # Which widget conversation token may resume this session (see
+    # conversation_token.conversation_scope). NULL: only a token the embedding app
+    # vouched for - and every non-widget channel, which never resumes by token.
+    conversation_key = Column(String(64), nullable=True)
+    assigned_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
+    transfer_reason = Column(String, nullable=True)
+    # The free-text fields below are AI-written summaries of the conversation, so
+    # they are encrypted at rest alongside the messages themselves.
+    transfer_description = Column(EncryptedText, nullable=True)
+    end_chat_reason = Column(SQLEnum(EndChatReasonType), nullable=True)
+    end_chat_description = Column(EncryptedText, nullable=True)
+
+    # Ticket-related fields
+    ticket_id = Column(String, nullable=True)
+    ticket_status = Column(String, nullable=True)
+    ticket_summary = Column(EncryptedText, nullable=True)
+    ticket_description = Column(EncryptedText, nullable=True)
+    integration_type = Column(String, nullable=True)
+    ticket_priority = Column(String, nullable=True)
+
+    # Sentiment fields
+    sentiment_label = Column(String, nullable=True)  # Overall session sentiment: 'positive', 'neutral', 'negative'
+    sentiment_score = Column(Float, nullable=True)  # Overall average sentiment score: -1.0 to 1.0
+
+    # Workflow-related fields
+    workflow_id = Column(UUID(as_uuid=True), ForeignKey("workflows.id", ondelete="SET NULL"), nullable=True)
+    current_node_id = Column(UUID(as_uuid=True), ForeignKey("workflow_nodes.id", ondelete="SET NULL"), nullable=True)
+
+    workflow_state = Column(JSON, default={})  # Store workflow execution state
+    workflow_history = Column(JSON, default=[])  # Store form submissions and workflow interactions
+
+    # Relationships
+    user = relationship("User", back_populates="session_assignments")
+    agent = relationship("Agent", back_populates="session_assignments")
+    customer = relationship("Customer", back_populates="session_assignments")
+    group = relationship("UserGroup", back_populates="session_assignments")
+    ratings = relationship("Rating", back_populates="session_assignments")
+    workflow = relationship("Workflow", back_populates="sessions")
+    current_node = relationship("WorkflowNode")
+
+
+# Add back-reference in UserGroup model if not already present
+if not hasattr(UserGroup, 'session_assignments'):
+    UserGroup.session_assignments = relationship(
+        "SessionToAgent",
+        back_populates="group",
+        uselist=True
+    )