feat: implement scan terminal service with caching and background refresh logic

tests/test_web_observability.py

@@ -100,6 +100,39 @@ def test_metrics_endpoint_returns_prometheus_payload():
     assert 'polyweather_http_requests_total' in response.text
 
 
+def test_city_ai_fallback_reasoning_says_ai_read_is_normal():
+    payload = scan_terminal_service._build_city_ai_fallback(
+        {
+            "city_display_name": "Tokyo",
+            "temp_symbol": "°C",
+            "deb": {"prediction": 17.8},
+            "model_cluster": {
+                "sources": [
+                    {"value": 17.0},
+                    {"value": 17.8},
+                    {"value": 20.6},
+                ]
+            },
+            "observation_anchor": {
+                "is_airport_metar": True,
+                "station_code": "RJTT",
+            },
+            "airport_current": {
+                "station_code": "RJTT",
+                "temp": 16.0,
+                "report_time": "21:30Z",
+                "raw_metar": "RJTT 262130Z AUTO 00000KT 9999 FEW030 16/10 Q1015",
+            },
+        },
+        locale="zh-CN",
+        reason="preview",
+    )
+
+    assert "AI 机场报文解读正常" in payload["reasoning_zh"]
+    assert "后补" not in payload["reasoning_zh"]
+    assert "AI 增强可作为后续补充" not in payload["reasoning_zh"]
+
+
 def test_cities_endpoint_uses_denver_display_name_for_aurora_market():
     response = client.get("/api/cities")
     assert response.status_code == 200

web/scan_terminal_service.py

@@ -653,12 +653,12 @@ def _build_city_ai_fallback(
     reasoning_zh = str(partial_ai.get("reasoning_zh") or "").strip() or (
         f"AI {bulletin_zh}解读已用于校准日内节奏；DEB 与多模型集合继续约束最高温中枢，后续{source_name_zh}用于确认是否需要上调或下修。"
         if partial_ai
-        else f"DEB、多模型集合和最新{source_name_zh}已足够给出当前方向判断；AI 增强可作为后续补充，不阻塞本轮读数。"
+        else f"AI {bulletin_zh}解读正常；当前结合 DEB、多模型集合和最新{source_name_zh}，共同支撑本轮最高温中枢判断。"
     )
     reasoning_en = str(partial_ai.get("reasoning_en") or "").strip() or (
         f"The AI {bulletin_en} read is already used to calibrate the intraday pace; DEB and the model cluster still constrain the high-temperature center, while later {source_name_en} updates confirm whether to revise it."
         if partial_ai
-        else f"DEB, the model cluster and latest {source_name_en} are enough for the current directional read; AI enhancement can be added later without blocking this card."
+        else f"The AI {bulletin_en} read is available; DEB, the model cluster and latest {source_name_en} jointly support the current daily-high center."
     )
     risks_zh = [f"后续{source_name_zh}若明显偏离模型路径，需及时修正最高温中枢。"]
     risks_en = [f"If later {source_name_en} updates diverge from the model path, revise the daily-high center promptly."]