refactor(server): steward 决策链路改用 LangGraph 编排

- 新增 StewardGraphPlannerService，用 LangGraph 状态图编排意图识别→流程判断→模型/规则分支→兜底，替代原 planner 内线性调用
- 新增 StewardGraphRuntimeService 编排运行时决策与槽位决策；StewardActionContracts/Executor 统一动作合约与执行
- steward_intent_agent/application_fact_resolver/runtime_chat 适配图执行器，config 暴露图相关开关
- pyproject/uv.lock 新增 langgraph 依赖
- 新增 graph_planner/graph_runtime/action_executor 测试，更新 intent_agent/planner/fact_resolver/runtime_chat/reimbursement 测试

server/tests/test_steward_graph_planner.py

@@ -0,0 +1,234 @@
+from __future__ import annotations
+
+from app.api.v1.endpoints import steward as steward_endpoint
+from app.core.config import get_settings
+from app.schemas.steward import StewardPlanRequest
+from app.services.steward_graph_planner import StewardGraphPlannerService
+from app.services.steward_intent_agent import StewardIntentAgentResult
+from app.services.steward_planner import StewardPlannerService
+
+
+class GraphTravelApplicationIntentAgent:
+    def __init__(self) -> None:
+        self.calls = 0
+
+    def detect(self, request, *, base_date, canonical_fields):
+        self.calls += 1
+        return StewardIntentAgentResult(
+            payload={
+                "thinking_events": [
+                    {
+                        "stage": "task_split",
+                        "title": "识别出差申请草稿",
+                        "content": "模型识别到用户要创建上海出差申请，并保存草稿。",
+                    }
+                ],
+                "tasks": [
+                    {
+                        "task_type": "expense_application",
+                        "title": "上海出差申请",
+                        "summary": (
+                            "2026-02-20 至 2026-02-23 前往上海，"
+                            "国网仿生产服务器部署，火车出行。"
+                        ),
+                        "requested_action": "save_draft",
+                        "confidence": 0.95,
+                        "ontology_fields": {
+                            "time_range": "2026-02-20 至 2026-02-23",
+                            "location": "上海",
+                            "expense_type": "差旅",
+                            "reason": "国网仿生产服务器部署",
+                            "transport_type": "火车",
+                        },
+                        "missing_fields": [],
+                    }
+                ],
+                "attachment_groups": [],
+            },
+            model_call_traces=[
+                {
+                    "slot": "main",
+                    "provider": "MiniMax",
+                    "model": "abab-test",
+                    "attempt": 1,
+                    "status": "succeeded",
+                }
+            ],
+        )
+
+
+class GraphSubmitTravelApplicationIntentAgent:
+    def __init__(self) -> None:
+        self.calls = 0
+
+    def detect(self, request, *, base_date, canonical_fields):
+        self.calls += 1
+        return StewardIntentAgentResult(
+            payload={
+                "thinking_events": [
+                    {
+                        "stage": "task_split",
+                        "title": "识别出差申请提交",
+                        "content": "模型识别到用户要创建上海出差申请，并直接提交。",
+                    }
+                ],
+                "tasks": [
+                    {
+                        "task_type": "expense_application",
+                        "title": "上海出差申请",
+                        "summary": (
+                            "2026-02-20 至 2026-02-23 前往上海，"
+                            "辅助国网仿生产服务器部署，火车出行。"
+                        ),
+                        "requested_action": "submit",
+                        "confidence": 0.96,
+                        "ontology_fields": {
+                            "time_range": "2026-02-20 至 2026-02-23",
+                            "location": "上海",
+                            "expense_type": "差旅",
+                            "reason": "辅助国网仿生产服务器部署",
+                            "transport_mode": "火车",
+                        },
+                        "missing_fields": [],
+                    }
+                ],
+                "attachment_groups": [],
+            },
+            model_call_traces=[
+                {
+                    "slot": "main",
+                    "provider": "MiniMax",
+                    "model": "abab-test",
+                    "attempt": 1,
+                    "status": "succeeded",
+                }
+            ],
+        )
+
+
+class GraphEmptyIntentAgent:
+    def __init__(self) -> None:
+        self.calls = 0
+
+    def detect(self, request, *, base_date, canonical_fields):
+        self.calls += 1
+        return None
+
+
+def test_langgraph_planner_preserves_llm_save_draft_plan() -> None:
+    intent_agent = GraphTravelApplicationIntentAgent()
+    service = StewardGraphPlannerService(intent_agent=intent_agent)
+
+    result = service.build_plan(
+        StewardPlanRequest(
+            message="2026-02-20 至 2026-02-23，上海出差，国网仿生产服务器部署，火车，保存草稿",
+            client_now_iso="2026-02-10T09:00:00+08:00",
+        )
+    )
+
+    assert intent_agent.calls == 1
+    assert result.planning_source == "llm_function_call"
+    assert result.tasks[0].requested_action == "save_draft"
+    assert result.tasks[0].ontology_fields["time_range"] == "2026-02-20 至 2026-02-23"
+    assert result.tasks[0].ontology_fields["transport_mode"] == "train"
+    assert result.model_call_traces[0]["provider"] == "MiniMax"
+
+
+def test_langgraph_planner_builds_submit_action_steps_for_application() -> None:
+    intent_agent = GraphSubmitTravelApplicationIntentAgent()
+    service = StewardGraphPlannerService(intent_agent=intent_agent)
+
+    result = service.build_plan(
+        StewardPlanRequest(
+            message="2026-02-20 至 2026-02-23，去上海出差，辅助国网仿生产服务器部署，交通火车，直接提交",
+            client_now_iso="2026-02-10T09:00:00+08:00",
+        )
+    )
+
+    assert intent_agent.calls == 1
+    assert result.planning_source == "llm_function_call"
+    assert result.action_steps[0].action_type == "detect_intent"
+    assert [step.action_type for step in result.tasks[0].action_steps] == [
+        "fill_application_fields",
+        "build_application_preview",
+        "validate_required_fields",
+        "run_duplicate_precheck",
+        "submit_application",
+    ]
+    assert result.tasks[0].action_steps[0].payload["ontology_fields"]["location"] == "上海"
+    assert result.tasks[0].action_steps[-1].requires_confirmation is True
+    assert result.tasks[0].action_steps[-1].status == "pending_confirmation"
+
+
+def test_langgraph_planner_falls_back_when_model_returns_no_tool_call() -> None:
+    intent_agent = GraphEmptyIntentAgent()
+    service = StewardGraphPlannerService(intent_agent=intent_agent)
+
+    result = service.build_plan(
+        StewardPlanRequest(
+            message="2026-02-20 至 2026-02-23，上海出差，国网仿生产服务器部署，火车，保存草稿",
+            client_now_iso="2026-02-10T09:00:00+08:00",
+        )
+    )
+
+    assert intent_agent.calls == 1
+    assert result.planning_source == "rule_fallback"
+    assert result.tasks[0].requested_action == "save_draft"
+    assert result.tasks[0].ontology_fields["time_range"] == "2026-02-20 至 2026-02-23"
+    assert result.tasks[0].ontology_fields["transport_mode"] == "train"
+    assert result.model_call_traces == []
+
+
+def test_langgraph_planner_rule_fallback_builds_save_draft_action_steps() -> None:
+    intent_agent = GraphEmptyIntentAgent()
+    service = StewardGraphPlannerService(intent_agent=intent_agent)
+
+    result = service.build_plan(
+        StewardPlanRequest(
+            message="2026-02-20 至 2026-02-23，上海出差，国网仿生产服务器部署，火车，保存草稿",
+            client_now_iso="2026-02-10T09:00:00+08:00",
+        )
+    )
+
+    assert result.planning_source == "rule_fallback"
+    assert result.tasks[0].requested_action == "save_draft"
+    assert [step.action_type for step in result.tasks[0].action_steps] == [
+        "fill_application_fields",
+        "build_application_preview",
+        "validate_required_fields",
+        "save_application_draft",
+    ]
+    assert result.tasks[0].action_steps[-1].status == "planned"
+
+
+def test_build_steward_planner_uses_langgraph_runtime_when_enabled(monkeypatch) -> None:
+    monkeypatch.setenv("STEWARD_AGENT_RUNTIME", "langgraph")
+    get_settings.cache_clear()
+    try:
+        planner = steward_endpoint._build_steward_planner(db=object())
+    finally:
+        get_settings.cache_clear()
+
+    assert isinstance(planner, StewardGraphPlannerService)
+
+
+def test_build_steward_planner_defaults_to_langgraph_runtime(monkeypatch) -> None:
+    monkeypatch.delenv("STEWARD_AGENT_RUNTIME", raising=False)
+    get_settings.cache_clear()
+    try:
+        planner = steward_endpoint._build_steward_planner(db=object())
+    finally:
+        get_settings.cache_clear()
+
+    assert isinstance(planner, StewardGraphPlannerService)
+
+
+def test_build_steward_planner_can_fall_back_to_legacy_runtime(monkeypatch) -> None:
+    monkeypatch.setenv("STEWARD_AGENT_RUNTIME", "legacy")
+    get_settings.cache_clear()
+    try:
+        planner = steward_endpoint._build_steward_planner(db=object())
+    finally:
+        get_settings.cache_clear()
+
+    assert isinstance(planner, StewardPlannerService)