Initial commit: 浼佷笟寰俊 AI 鏈哄櫒浜哄姪鐞?MVP

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/models/message.py

@@ -0,0 +1,18 @@
+"""单条消息（仅存 public 可见内容，隔离内部信息）。"""
+from datetime import datetime
+from sqlalchemy import String, Text, DateTime, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class Message(Base):
+    __tablename__ = "messages"
+
+    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
+    session_id: Mapped[int] = mapped_column(ForeignKey("chat_sessions.id", ondelete="CASCADE"), nullable=False, index=True)
+    role: Mapped[str] = mapped_column(String(16), nullable=False)  # user / assistant / system
+    content: Mapped[str] = mapped_column(Text, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=datetime.utcnow)
+
+    session: Mapped["ChatSession"] = relationship("ChatSession", back_populates="messages")