feat: Phase 5 — AI Research Agent（受控工具白名单 + LLM 编排 + API）

- agent/tools.py：Tool 元数据（JSON Schema）+ 白名单调用（异常转可读反馈，不中断对话）
- agent/tools_impl.py：6 个受控工具 search_stocks / get_market_data / test_factor / run_backtest / get_experiment / compare_experiments —— 全部只读经 Job/Experiment 链路，研究自动归档；无 shell/任意执行/写删数据能力
- agent/llm.py：LLMClient 抽象 + OpenAI 兼容客户端（LLM_API_KEY/LLM_BASE_URL/LLM_MODEL 走 .env，未配置给出引导提示）+ 研究纪律 system prompt（反过拟合/样本外/成本）
- agent/service.py：编排循环（tool/final JSON 决策 → 执行 → 回喂 → 结论），轮次上限兜底，未知工具拒绝
- /api/agent/chat；httpx 移至主依赖；Job 默认工厂抽取（api/agent/executor 复用）
- 测试 6 项（白名单无 shell、完整研究循环产出、未知工具拒绝、轮次兜底），全量 79 passed / ruff clean

backend/app/application/services/job_executor.py

@@ -18,6 +18,7 @@ from app.domain.entities.research import (
     BacktestResult,
     ExperimentRecord,
     FactorTestReport,
+    JobRecord,
     JobStatus,
     ResearchSpec,
 )
@@ -144,3 +145,56 @@ def execute_job(
                     session.commit()
         except Exception:  # noqa: BLE001
             pass
+
+
+def default_factories() -> dict:
+    """后台执行所需的独立 Session / Repository / 引擎装配（跨请求生命周期）。"""
+    from app.infrastructure.persistence.sqlalchemy.repositories.jobs_impl import (
+        SqlAlchemyExperimentRepository,
+        SqlAlchemyJobRepository,
+    )
+    from app.infrastructure.persistence.sqlalchemy.repositories.market_impl import (
+        SqlAlchemyDailyBarRepository,
+        SqlAlchemyStockRepository,
+    )
+    from app.infrastructure.persistence.sqlalchemy.session import SessionLocal
+    from app.quant.engine import LocalEngine
+
+    return {
+        "session_factory": SessionLocal,
+        "job_repo_factory": lambda s: SqlAlchemyJobRepository(s),
+        "experiment_repo_factory": lambda s: SqlAlchemyExperimentRepository(s),
+        "stock_repo_factory": lambda s: SqlAlchemyStockRepository(s),
+        "daily_repo_factory": lambda s: SqlAlchemyDailyBarRepository(s),
+        "engine": LocalEngine(),
+    }
+
+
+def submit_and_run(spec: ResearchSpec, *, factories: dict | None = None) -> JobRecord:
+    """同步创建并执行一个 Job（复用 Job 状态机与 Experiment 归档），返回终态 Job。"""
+    facts = factories or default_factories()
+    session_factory = facts["session_factory"]
+    job_repo = facts["job_repo_factory"]
+    job = JobRecord(
+        id=new_id("JOB"),
+        kind=spec.type,
+        spec_json=json.dumps(spec.model_dump(mode="json"), ensure_ascii=False),
+        status=JobStatus.QUEUED,
+        created_at=datetime.now(),
+    )
+    with session_factory() as session:
+        job_repo(session).create(job)
+        session.commit()
+    execute_job(
+        job.id,
+        session_factory=session_factory,
+        job_repo_factory=job_repo,
+        experiment_repo_factory=facts["experiment_repo_factory"],
+        stock_repo_factory=facts["stock_repo_factory"],
+        daily_repo_factory=facts["daily_repo_factory"],
+        engine=facts["engine"],
+    )
+    with session_factory() as session:
+        done = job_repo(session).get(job.id)
+    assert done is not None
+    return done