feat(agent-chat): complete core workflow and strengthen auth rate limiting

backend/tests/unit/database/test_agent_chat_migration_contract.py

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+from __future__ import annotations
+
+from pathlib import Path
+
+
+def test_agent_chat_migration_exists_and_creates_expected_tables() -> None:
+    versions_dir = Path(__file__).resolve().parents[3] / "alembic" / "versions"
+    migration = versions_dir / "20260226_create_agent_chat_core_tables.py"
+
+    assert migration.exists()
+
+    content = migration.read_text(encoding="utf-8")
+    assert 'create_table(\n        "llm_factory"' in content
+    assert 'create_table(\n        "llms"' in content
+    assert 'create_table(\n        "sessions"' in content
+    assert 'create_table(\n        "messages"' in content
+    assert "tool_calls" not in content

backend/tests/unit/database/test_agent_chat_models.py

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+from __future__ import annotations
+
+from uuid import uuid4
+
+import pytest
+from sqlalchemy import Column, String, Table, select
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+
+from core.db.base import Base
+from models.agent_chat_message import AgentChatMessage
+from models.agent_chat_session import AgentChatSession, AgentChatSessionStatus
+from models.llm import Llm
+from models.llm_factory import LlmFactory
+
+
+@pytest.fixture
+async def db_engine():
+    users_table = Table(
+        "users",
+        Base.metadata,
+        Column("id", String, primary_key=True),
+        schema="auth",
+        extend_existing=True,
+    )
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:", echo=False)
+    async with engine.begin() as conn:
+        await conn.exec_driver_sql("ATTACH DATABASE ':memory:' AS auth")
+        await conn.run_sync(Base.metadata.create_all)
+    yield engine
+    Base.metadata.remove(users_table)
+    await engine.dispose()
+
+
+@pytest.fixture
+async def db_session(db_engine):
+    async_session = async_sessionmaker(
+        bind=db_engine,
+        class_=AsyncSession,
+        expire_on_commit=False,
+    )
+    async with async_session() as session:
+        yield session
+        await session.rollback()
+
+
+@pytest.mark.asyncio
+async def test_llm_factory_and_llm_relationship(db_session: AsyncSession) -> None:
+    factory = LlmFactory(
+        name="qwen",
+        request_url="https://dashscope.aliyuncs.com/compatible-mode/v1",
+        avatar="https://cdn.example.com/qwen.png",
+    )
+    db_session.add(factory)
+    await db_session.flush()
+
+    llm = Llm(
+        factory_id=factory.id,
+        model_code="qwen3.5-flash",
+    )
+    db_session.add(llm)
+    await db_session.commit()
+
+    found_llm = await db_session.get(Llm, llm.id)
+    assert found_llm is not None
+    assert found_llm.factory_id == factory.id
+
+
+@pytest.mark.asyncio
+async def test_session_status_supports_required_values(
+    db_session: AsyncSession,
+) -> None:
+    user_id = uuid4()
+    session = AgentChatSession(
+        user_id=user_id,
+        title="test",
+        status="pending",
+    )
+    db_session.add(session)
+    await db_session.commit()
+
+    statuses = [
+        AgentChatSessionStatus.PENDING,
+        AgentChatSessionStatus.RUNNING,
+        AgentChatSessionStatus.COMPLETED,
+        AgentChatSessionStatus.FAILED,
+    ]
+    for status in statuses:
+        session.status = status
+        await db_session.commit()
+        await db_session.refresh(session)
+        assert session.status == status
+
+
+@pytest.mark.asyncio
+async def test_messages_role_supports_tool(db_session: AsyncSession) -> None:
+    user_id = uuid4()
+    session = AgentChatSession(
+        user_id=user_id,
+        title="tool test",
+        status="pending",
+    )
+    db_session.add(session)
+    await db_session.flush()
+
+    message = AgentChatMessage(
+        session_id=session.id,
+        seq=1,
+        role="tool",
+        content="tool output",
+        cost=0,
+    )
+    db_session.add(message)
+    await db_session.commit()
+
+    result = await db_session.execute(
+        select(AgentChatMessage).where(AgentChatMessage.session_id == session.id)
+    )
+    found = result.scalar_one()
+    assert found.role == "tool"