feat(agent): complete closed-loop runtime and pricing fallback

backend/src/v1/agent/repository.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+from uuid import UUID
+
+from fastapi import HTTPException
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from models.agent_chat_session import AgentChatSession
+
+
+class AgentRepository:
+    def __init__(self, session: AsyncSession) -> None:
+        self._session = session
+
+    async def get_session_owner(self, *, session_id: str) -> str:
+        try:
+            session_uuid = UUID(session_id)
+        except ValueError as exc:
+            raise HTTPException(status_code=422, detail="Invalid session_id") from exc
+
+        stmt = select(AgentChatSession.user_id).where(
+            AgentChatSession.id == session_uuid
+        )
+        owner_id = (await self._session.execute(stmt)).scalar_one_or_none()
+        if owner_id is None:
+            raise HTTPException(status_code=404, detail="Session not found")
+        return str(owner_id)
+
+    async def create_session_for_user(self, *, user_id: str) -> str:
+        try:
+            user_uuid = UUID(user_id)
+        except ValueError as exc:
+            raise HTTPException(status_code=422, detail="Invalid user_id") from exc
+
+        session = AgentChatSession(user_id=user_uuid)
+        self._session.add(session)
+        await self._session.flush()
+        await self._session.refresh(session)
+        return str(session.id)
+
+    async def commit(self) -> None:
+        await self._session.commit()
+
+    async def rollback(self) -> None:
+        await self._session.rollback()
+
+    async def delete_session(self, *, session_id: str) -> None:
+        try:
+            session_uuid = UUID(session_id)
+        except ValueError as exc:
+            raise HTTPException(status_code=422, detail="Invalid session_id") from exc
+        session = await self._session.get(AgentChatSession, session_uuid)
+        if session is not None:
+            await self._session.delete(session)
+            await self._session.flush()