feat(steward): 拦截业务无关输入返回 off_topic 计划

- schemas/steward.py：StewardPlanResponse 新增 suggested_prompts 字段
- steward_planner.py：新增 STEWARD_BUSINESS_SIGNAL_KEYWORDS 与
  _is_business_irrelevant_input 守卫，在 build_plan 入口前置；
  新增 _build_off_topic_plan 构造 plan_status=off_topic 的引导计划
- steward_intent_agent.py：system prompt 追加业务无关约束
- test_steward_planner.py：覆盖 123/你好/纯标点走 off_topic，
  并验证正常业务输入不受守卫影响

server/src/app/schemas/steward.py

@@ -128,6 +128,10 @@ class StewardPlanResponse(BaseModel):
     )
     candidate_flows: list[StewardCandidateFlow] = Field(default_factory=list, description="等待用户确认的候选流程快捷列表。")
     model_call_traces: list[dict[str, Any]] = Field(default_factory=list, description="模型工具调用轨迹。")
+    suggested_prompts: list[str] = Field(
+        default_factory=list,
+        description="当 plan_status 为 off_topic 等场景时，给用户的推荐话术示例。",
+    )
 
 
 class StewardSlotOption(BaseModel):

server/src/app/services/steward_intent_agent.py

@@ -115,6 +115,10 @@ class StewardIntentAgent:
                     "如果输入里出现 occurred_date、transport_type、reason_value 等别名，必须映射为 canonical 字段。"
                     "相对日期必须以 base_date 为准转换为明确日期。"
                     "thinking_events 只能是面向用户的过程摘要，不能暴露内部推理链。"
+                    "如果用户输入与出差、费用、报销、申请等财务事项完全无关"
+                    "（例如纯数字、问候、闲聊、无意义字符、单字符重复），"
+                    "必须让 tasks 返回空数组，并在 thinking_events 中明确说明“未识别到财务事项”，"
+                    "不要强行把无关输入识别为 expense_application 或 reimbursement 任务。"
                 ),
             },
             {

server/src/app/services/steward_planner.py

@@ -49,6 +49,27 @@ CITY_NAMES = (
     "无锡",
 )
 
+# 业务信号关键词：用于判定输入是否与小财管家支持的财务事项相关。
+# 只要清洗后的消息命中其中任意一个关键词，就视为业务相关；否则进入 off_topic 拦截。
+STEWARD_BUSINESS_SIGNAL_KEYWORDS: tuple[str, ...] = (
+    # 动作词
+    "申请", "报销", "草稿", "提交", "审批", "保存", "发起", "创建", "核对", "归集",
+    # 差旅场景
+    "出差", "差旅", "费用", "交通", "住宿", "招待", "酒店", "机票", "航班", "高铁",
+    "动车", "火车", "出租车", "的士", "网约车", "打车", "地铁", "公交", "用餐", "餐饮", "宴请",
+    # 票据/凭证
+    "票据", "发票", "凭证", "行程单", "付款截图", "付款", "小票", "收据",
+    # 业务对象
+    "客户", "项目", "拜访", "会议", "培训", "部署", "实施", "支撑", "支持", "协助",
+    "调研", "驻场", "上线", "验收", "审核",
+    # 时间信号
+    "昨天", "前天", "明天", "后天", "下周", "下月", "近期", "月底", "今天", "上周", "上月",
+    # 金额/数量（"天"用于"出差3天"等表达）
+    "金额", "元", "块", "万", "千", "天",
+    # 复用城市名信号
+    *CITY_NAMES,
+)
+
 APPLICATION_SPLIT_PATTERN = re.compile(r"(?:^|[，,。；;])[^，,。；;]*?(?:申请|出差申请|差旅申请)[^，,。；;]*")
 REIMBURSEMENT_PATTERN = re.compile(r"(?:我要报销|还需要报销|需要报销|报销)([^，,。；;！？?!\n]+)")
 MONTH_DAY_PATTERN = re.compile(r"(?P<month>\d{1,2})\s*月\s*(?P<day>\d{1,2})\s*(?:日|号)?")
@@ -107,6 +128,9 @@ class StewardPlannerService:
             raise ValueError("小财管家需要一段任务描述。")
 
         base_date = self._resolve_base_date(request.client_now_iso, request.context_json)
+        # 业务无关输入拦截（纯数字、问候、闲聊、乱码等）：在进入 LLM/规则兜底之前直接返回 off_topic 计划。
+        if self._is_business_irrelevant_input(message, request):
+            return self._build_off_topic_plan(request)
         model_call_traces: list[dict[str, Any]] = []
         fallback_reason = ""
         if self.intent_agent is not None and self._should_use_model_intent_recognition(message, base_date, request):
@@ -159,6 +183,51 @@ class StewardPlannerService:
             return False
         return self._has_multiple_financial_demands(message)
 
+    @staticmethod
+    def _is_business_irrelevant_input(message: str, request: StewardPlanRequest) -> bool:
+        """判断输入是否与小财管家支持的财务事项完全无关。
+
+        判定规则：消息去除所有空白后不含任何业务信号关键词，且没有上传附件，
+        即视为业务无关输入（如纯数字、问候、闲聊、乱码）。
+        """
+        if request.attachments:
+            return False
+        compact = re.sub(r"\s+", "", message)
+        if not compact:
+            return False
+        return not any(keyword in compact for keyword in STEWARD_BUSINESS_SIGNAL_KEYWORDS)
+
+    def _build_off_topic_plan(self, request: StewardPlanRequest) -> StewardPlanResponse:
+        """业务无关输入的兜底计划：明确告知用户未识别到财务事项，并给出话术示例。"""
+        return StewardPlanResponse(
+            plan_id=f"steward_plan_{uuid.uuid4().hex[:12]}",
+            plan_status="off_topic",
+            planning_source="rule_fallback",
+            next_action="none",
+            summary="这看起来跟财务任务没什么关系，小财管家没识别到费用申请或费用报销的意图。",
+            thinking_events=[
+                StewardThinkingEvent(
+                    event_id="intent_agent_off_topic",
+                    stage="off_topic",
+                    title="未识别到财务事项",
+                    content=(
+                        "我检查了这句话，没有发现费用申请、报销、出差、交通、招待等财务线索。"
+                        "如果你确实是要处理财务任务，可以参考下面的示例换一种说法。"
+                    ),
+                )
+            ],
+            tasks=[],
+            attachment_groups=[],
+            confirmation_groups=[],
+            candidate_flows=[],
+            suggested_prompts=[
+                "我想要申请明天去北京出差3天，支撑客户现场实施",
+                "我要报销昨天的交通费",
+                "报销上周出差上海的费用",
+            ],
+            model_call_traces=[],
+        )
+
     def _build_rule_fallback_plan(
         self,
         request: StewardPlanRequest,