diff --git a/frontend/components/dashboard/scan-terminal/__tests__/refreshCadencePolicy.test.ts b/frontend/components/dashboard/scan-terminal/__tests__/refreshCadencePolicy.test.ts
index 1d9efe30..3513f3cb 100644
--- a/frontend/components/dashboard/scan-terminal/__tests__/refreshCadencePolicy.test.ts
+++ b/frontend/components/dashboard/scan-terminal/__tests__/refreshCadencePolicy.test.ts
@@ -142,15 +142,15 @@ export async function runTests() {
   );
   assert(
     flushCityDetailBatchBlock.includes("if (!payload)") &&
-      flushCityDetailBatchBlock.includes("resolveCityDetailBatchWithSingleFallback") &&
-      flushCityDetailBatchBlock.includes("resolveBatchWaiters(waiters, null)"),
-    "single-city detail fallback should be reserved for whole-batch failures rather than successful batch misses",
+      flushCityDetailBatchBlock.includes("resolveAllBatchWaitersAsNull") &&
+      !flushCityDetailBatchBlock.includes("resolveCityDetailBatchWithSingleFallback"),
+    "whole-batch failures should stop at the chart batch layer instead of fanning out into single-city full-detail requests",
   );
-  const fetchHourlyBlock = chartLogicSource.match(/async function fetchHourlyForecastForCity[\s\S]*?\r?\n}\r?\n\r?\nfunction fetchCityDetailWithTimeout/)?.[0] || "";
+  const fetchHourlyBlock = chartLogicSource.match(/async function fetchHourlyForecastForCity[\s\S]*?\r?\n}\r?\n\r?\nfunction shouldPollLiveChart/)?.[0] || "";
   assert(
     fetchHourlyBlock.includes("queueCityDetailBatch(city, resParam)") &&
       !fetchHourlyBlock.includes("runQueuedHourlyDetailRequest"),
-    "first-paint and background city detail refreshes should both enter the batch queue before falling back to single requests",
+    "first-paint and background city detail refreshes should both enter the batch queue without falling back to single requests",
   );
   assert(
     dashboardSource.includes("ONLINE_USERS_REFRESH_MS = 5 * 60_000") &&
diff --git a/frontend/components/dashboard/scan-terminal/__tests__/ssePatchArchitecture.test.ts b/frontend/components/dashboard/scan-terminal/__tests__/ssePatchArchitecture.test.ts
index 1350457b..716717ad 100644
--- a/frontend/components/dashboard/scan-terminal/__tests__/ssePatchArchitecture.test.ts
+++ b/frontend/components/dashboard/scan-terminal/__tests__/ssePatchArchitecture.test.ts
@@ -259,7 +259,7 @@ export function runTests() {
   );
   assert(
     chartLogic.includes("HOURLY_DETAIL_REQUEST_TIMEOUT_MS = 12_000") &&
-      chartLogic.includes("fetchCityDetailWithTimeout") &&
+      chartLogic.includes("fetchCityDetailBatchWithTimeout") &&
       chartLogic.includes("signal: controller.signal") &&
       chartLogic.includes("controller.abort()"),
     "city detail chart fetches must have a frontend timeout so panels cannot stay on 加载图表 forever",
diff --git a/frontend/components/dashboard/scan-terminal/temperature-chart-logic.ts b/frontend/components/dashboard/scan-terminal/temperature-chart-logic.ts
index b237583f..6ce12965 100644
--- a/frontend/components/dashboard/scan-terminal/temperature-chart-logic.ts
+++ b/frontend/components/dashboard/scan-terminal/temperature-chart-logic.ts
@@ -1033,16 +1033,6 @@ function primeCityDetailCache(
   return data;
 }
 
-async function fetchSingleHourlyForecastForCity(
-  city: string,
-  resolution: string,
-): Promise<HourlyForecast> {
-  const res = await fetchCityDetailWithTimeout(city, resolution);
-  if (!res || !res.ok) return null;
-  const json = await res.json() as CityDetail;
-  return primeCityDetailCache(city, resolution, json);
-}
-
 function queueCityDetailBatch(city: string, resolution: string): Promise<HourlyForecast> {
   return new Promise<HourlyForecast>((resolve, reject) => {
     const queue = _cityDetailBatchQueues.get(resolution) || {
@@ -1073,13 +1063,6 @@ function resolveBatchWaiters(
   (waiters || []).forEach((waiter) => waiter.resolve(value));
 }
 
-function rejectBatchWaiters(
-  waiters: CityDetailBatchWaiter[] | undefined,
-  reason: unknown,
-) {
-  (waiters || []).forEach((waiter) => waiter.reject(reason));
-}
-
 function resolveCityDetailFromBatch(
   details: Record<string, CityDetail | null | undefined> | undefined,
   city: string,
@@ -1119,7 +1102,7 @@ async function flushCityDetailBatch(resolution: string) {
   try {
     const payload = await fetchCityDetailBatchWithTimeout(cities, resolution);
     if (!payload) {
-      await resolveCityDetailBatchWithSingleFallback(cities, queue, resolution);
+      resolveAllBatchWaitersAsNull(cities, queue);
       return;
     }
 
@@ -1145,29 +1128,17 @@ async function flushCityDetailBatch(resolution: string) {
       }),
     );
   } catch (error) {
-    await resolveCityDetailBatchWithSingleFallback(cities, queue, resolution, error);
+    resolveAllBatchWaitersAsNull(cities, queue);
   }
 }
 
-async function resolveCityDetailBatchWithSingleFallback(
+function resolveAllBatchWaitersAsNull(
   cities: string[],
   queue: CityDetailBatchQueue,
-  resolution: string,
-  reason?: unknown,
 ) {
-  await Promise.all(
-    cities.map(async (city) => {
-      const waiters = queue.waiters.get(city);
-      try {
-        resolveBatchWaiters(
-          waiters,
-          await runQueuedHourlyDetailRequest(() => fetchSingleHourlyForecastForCity(city, resolution)),
-        );
-      } catch (fallbackError) {
-        rejectBatchWaiters(waiters, fallbackError || reason);
-      }
-    }),
-  );
+  cities.forEach((city) => {
+    resolveBatchWaiters(queue.waiters.get(city), null);
+  });
 }
 
 function fetchCityDetailBatchWithTimeout(cities: string[], resolution: string) {
@@ -1227,17 +1198,6 @@ async function fetchHourlyForecastForCity(
   return request;
 }
 
-function fetchCityDetailWithTimeout(city: string, resolution: string) {
-  const controller = new AbortController();
-  const timeoutId = globalThis.setTimeout(() => controller.abort(), HOURLY_DETAIL_REQUEST_TIMEOUT_MS);
-  return fetch(`/api/city/${encodeURIComponent(city)}/detail?depth=full&force_refresh=false&resolution=${resolution}`, {
-    headers: { Accept: "application/json" },
-    signal: controller.signal,
-  })
-    .catch(() => null)
-    .finally(() => globalThis.clearTimeout(timeoutId));
-}
-
 function shouldPollLiveChart({
   city,
   compact,
diff --git a/tests/test_web_observability.py b/tests/test_web_observability.py
index 91c6c8f3..89d603f0 100644
--- a/tests/test_web_observability.py
+++ b/tests/test_web_observability.py
@@ -31,6 +31,27 @@ def test_healthz_returns_ok_shape():
     assert 'cities_count' in payload
 
 
+def test_healthz_keeps_liveness_200_when_db_health_is_degraded(monkeypatch):
+    from web.services import system_api
+
+    monkeypatch.setattr(
+        system_api,
+        "build_health_payload",
+        lambda: {
+            "status": "degraded",
+            "time_utc": "2026-05-30T00:00:00+00:00",
+            "db": {"ok": False, "error": "database is locked"},
+            "state_storage_mode": "sqlite",
+            "cities_count": 50,
+        },
+    )
+
+    response = client.get("/healthz")
+
+    assert response.status_code == 200
+    assert response.json()["status"] == "degraded"
+
+
 def test_system_status_returns_summary_shape():
     response = client.get('/api/system/status')
     assert response.status_code == 200
@@ -697,41 +718,45 @@ def test_city_detail_batch_chart_scope_returns_only_chart_fields(monkeypatch):
             assert kind == "full"
             return {
                 "payload": {
-                    "city": city,
+                    "name": city,
+                    "display_name": city.title(),
+                    "local_date": "2026-05-30",
+                    "local_time": "15:20",
+                    "temp_symbol": "°C",
+                    "current": {
+                        "temp": 20.0,
+                        "settlement_source": "metar",
+                        "settlement_source_label": "METAR",
+                    },
                     "hourly": {"times": ["2026-05-30T00:00:00Z"], "temps": [20.0]},
+                    "forecast": {
+                        "today_high": 22.0,
+                        "daily": [{"date": "2026-05-30", "max_temp": 22.0}],
+                    },
+                    "multi_model": {
+                        "hourly_times": ["15:00"],
+                        "hourly_forecasts": {"ECMWF": [21.0]},
+                    },
+                    "deb": {"prediction": 21.5, "hourly_path": {"times": ["15:00"], "temps": [21.5]}},
+                    "probabilities": {"mu": 21.4, "distribution": [{"value": 21, "probability": 0.4}]},
+                    "runway_plate_history": {"01/19": [{"time": "2026-05-30T15:20:00Z", "temp": 20.1}]},
+                    "airport_current": {"temp": 20.0},
+                    "airport_primary": {"temp": 20.0},
+                    "airport_primary_today_obs": [["15:20", 20.0]],
+                    "wunderground_current": {"max_so_far": 20.5},
+                    "settlement_station": {"settlement_station_label": "Station"},
+                    "amos": {"runway_obs": {"point_temperatures": []}},
+                    "metar_today_obs": [{"time": "15:20", "temp": 20.0}],
+                    "settlement_today_obs": [],
+                    "dynamic_commentary": {"summary": "large text"},
+                    "official_nearby": [{"name": "unused"}],
+                    "taf": {"raw": "unused"},
+                    "ai_analysis": "unused",
                 }
             }
 
-    def build_detail(data, market_slug, target_date, resolution):
-        return {
-            "city": data["city"],
-            "overview": {
-                "local_date": "2026-05-30",
-                "local_time": "15:20",
-                "deb_prediction": 21.5,
-                "airport_primary_today_obs": [["15:20", 20.0]],
-            },
-            "timeseries": {
-                "hourly": data["hourly"],
-                "metar_today_obs": [{"time": "15:20", "temp": 20.0}],
-                "settlement_today_obs": [],
-                "forecast_daily": [{"date": "2026-05-30", "max_temp": 22.0}],
-            },
-            "models_hourly": {"times": ["15:00"], "curves": {"ECMWF": [21.0]}},
-            "deb": {"prediction": 21.5, "hourly_path": {"times": ["15:00"], "temps": [21.5]}},
-            "probabilities": {"mu": 21.4, "distribution": [{"value": 21, "probability": 0.4}]},
-            "runway_plate_history": {"01/19": [{"timestamp": "15:20", "temp_c": 20.1}]},
-            "runway_band_history": [{"time": "2026-05-30T15:20:00Z", "high_temp": 20.1}],
-            "airport_current": {"temp": 20.0},
-            "airport_primary": {"temp": 20.0},
-            "wunderground_current": {"max_so_far": 20.5},
-            "settlement_station": {"settlement_station_label": "Station"},
-            "amos": {"runway_obs": {"point_temperatures": []}},
-            "dynamic_commentary": {"summary": "large text"},
-            "official_nearby": [{"name": "unused"}],
-            "taf": {"raw": "unused"},
-            "ai_analysis": "unused",
-        }
+    def build_detail(_data, _market_slug, _target_date, _resolution):
+        raise AssertionError("chart scope must not build the full city detail payload")
 
     monkeypatch.setattr(city_api.legacy_routes, "_CACHE_DB", FakeCache())
     monkeypatch.setattr(city_api.legacy_routes, "_build_city_detail_payload", build_detail)
diff --git a/web/analysis_service.py b/web/analysis_service.py
index cdc0c663..9608d74a 100644
--- a/web/analysis_service.py
+++ b/web/analysis_service.py
@@ -37,6 +37,7 @@ from src.data_collection.city_registry import ALIASES, CITY_REGISTRY
 from src.data_collection.city_time import get_city_utc_offset_seconds
 from src.database.runtime_state import IntradayPathSnapshotRepository
 from web.services.city_payloads import (
+    build_city_chart_detail_payload as _city_chart_payload_detail,
     build_city_detail_payload as _city_payload_detail,
     build_city_summary_payload as _city_payload_summary
 )
@@ -2312,6 +2313,13 @@ def _build_city_detail_payload(
     )
 
 
+def _build_city_chart_detail_payload(
+    data: Dict[str, Any],
+    resolution: Optional[str] = "10m",
+) -> Dict[str, Any]:
+    return _city_chart_payload_detail(data, resolution=resolution)
+
+
 
 # ──────────────────────────────────────────────────────────
 #  Routes
diff --git a/web/core.py b/web/core.py
index 69518b37..f135be2a 100644
--- a/web/core.py
+++ b/web/core.py
@@ -511,7 +511,7 @@ def _is_excluded_model_name(model_name: str) -> bool:
 
 def _sqlite_health() -> Dict[str, Any]:
     try:
-        with sqlite3.connect(_account_db.db_path) as conn:
+        with sqlite3.connect(_account_db.db_path, timeout=0.05) as conn:
             conn.execute("SELECT 1").fetchone()
         return {"ok": True, "db_path": _account_db.db_path}
     except Exception as exc:
diff --git a/web/services/city_api.py b/web/services/city_api.py
index 98203d62..331bd6c2 100644
--- a/web/services/city_api.py
+++ b/web/services/city_api.py
@@ -146,6 +146,24 @@ async def _get_city_full_data(city: str, *, force_refresh: bool) -> Dict[str, An
     return await _refresh_city_full_data(city, False)
 
 
+async def _get_city_chart_data(city: str, *, force_refresh: bool) -> Dict[str, Any]:
+    if force_refresh:
+        return await _get_city_full_data(city, force_refresh=True)
+
+    cached_entry = await run_in_threadpool(legacy_routes._CACHE_DB.get_city_cache, "full", city)
+    if cached_entry:
+        payload = cached_entry.get("payload") or {}
+        if payload:
+            if not legacy_routes._city_cache_is_fresh(cached_entry, legacy_routes.CITY_FULL_CACHE_TTL_SEC):
+                _start_city_full_stale_refresh(city)
+            return await _overlay_cached_wunderground(city, payload)
+
+    return {
+        "name": city,
+        "display_name": str((legacy_routes.CITY_REGISTRY.get(city, {}) or {}).get("display_name") or city.title()),
+    }
+
+
 def _city_detail_payload_cache_key(
     data: Dict[str, Any],
     market_slug: Optional[str],
@@ -228,6 +246,17 @@ async def _build_city_detail_payload_cached(
     return payload
 
 
+async def _build_city_chart_detail_payload(
+    data: Dict[str, Any],
+    resolution: Optional[str],
+) -> Dict[str, Any]:
+    return await run_in_threadpool(
+        legacy_routes._build_city_chart_detail_payload,
+        data,
+        resolution,
+    )
+
+
 def _default_deb_recent() -> Dict[str, object]:
     return {
         "tier": "other",
@@ -577,6 +606,21 @@ async def _build_city_detail_batch_item_async(
     detail_scope: str = "full",
     timing_recorder: Optional[ServerTimingRecorder] = None,
 ) -> Tuple[str, Dict[str, Any]]:
+    if detail_scope == "chart":
+        if timing_recorder is not None:
+            data = await timing_recorder.measure_async(
+                f"chart_data_{city}",
+                lambda: _get_city_chart_data(city, force_refresh=force_refresh),
+            )
+            detail = await timing_recorder.measure_async(
+                f"chart_payload_{city}",
+                lambda: _build_city_chart_detail_payload(data, resolution),
+            )
+        else:
+            data = await _get_city_chart_data(city, force_refresh=force_refresh)
+            detail = await _build_city_chart_detail_payload(data, resolution)
+        return city, detail
+
     if timing_recorder is not None:
         data = await timing_recorder.measure_async(
             f"full_data_{city}",
diff --git a/web/services/city_payloads.py b/web/services/city_payloads.py
index 92d0e868..fa349c61 100644
--- a/web/services/city_payloads.py
+++ b/web/services/city_payloads.py
@@ -161,6 +161,151 @@ def build_runway_band_history(raw_history: Dict[str, List[Dict[str, Any]]], reso
     return band_history
 
 
+def build_runway_chart_histories(
+    raw_history: Dict[str, List[Dict[str, Any]]],
+    resolution: str,
+) -> tuple[Dict[str, List[Dict[str, Any]]], List[Dict[str, Any]]]:
+    if not raw_history:
+        return {}, []
+
+    try:
+        if resolution.endswith("m"):
+            minutes = int(resolution[:-1])
+        elif resolution.endswith("h"):
+            minutes = int(resolution[:-1]) * 60
+        else:
+            minutes = 10
+    except Exception:
+        minutes = 10
+
+    seconds = max(60, minutes * 60)
+    per_runway_buckets: Dict[str, Dict[int, List[float]]] = {}
+    all_buckets: Dict[int, List[float]] = {}
+
+    for rwy, points in raw_history.items():
+        if not points:
+            continue
+        rwy_key = str(rwy or "").strip()
+        if not rwy_key:
+            continue
+        runway_buckets = per_runway_buckets.setdefault(rwy_key, {})
+        for pt in points:
+            t_str = pt.get("time") or pt.get("timestamp")
+            temp = pt.get("temp") or pt.get("temp_c") or pt.get("value")
+            if temp is None or not isinstance(t_str, str):
+                continue
+            dt = _parse_time_val(t_str)
+            if not dt:
+                continue
+            try:
+                temp_value = float(temp)
+            except Exception:
+                continue
+
+            bucket_ts = (int(dt.timestamp()) // seconds) * seconds
+            runway_buckets.setdefault(bucket_ts, []).append(temp_value)
+            all_buckets.setdefault(bucket_ts, []).append(temp_value)
+
+    aggregated_history: Dict[str, List[Dict[str, Any]]] = {}
+    for rwy, buckets in per_runway_buckets.items():
+        bucket_points = []
+        for bucket_ts in sorted(buckets.keys()):
+            temps = buckets[bucket_ts]
+            if not temps:
+                continue
+            bucket_dt = datetime.fromtimestamp(bucket_ts, tz=timezone.utc)
+            bucket_points.append(
+                {
+                    "time": bucket_dt.isoformat(),
+                    "temp": round(temps[-1], 1),
+                }
+            )
+        if bucket_points:
+            aggregated_history[rwy] = bucket_points
+
+    band_history = []
+    for bucket_ts in sorted(all_buckets.keys()):
+        temps = all_buckets[bucket_ts]
+        if not temps:
+            continue
+        bucket_dt = datetime.fromtimestamp(bucket_ts, tz=timezone.utc)
+        band_history.append(
+            {
+                "time": bucket_dt.isoformat(),
+                "high_temp": round(max(temps), 1),
+                "low_temp": round(min(temps), 1),
+                "avg_temp": round(sum(temps) / len(temps), 1),
+            }
+        )
+
+    return aggregated_history, band_history
+
+
+def build_city_chart_detail_payload(
+    data: Dict[str, Any],
+    resolution: Optional[str] = "10m",
+) -> Dict[str, Any]:
+    forecast = data.get("forecast") if isinstance(data.get("forecast"), dict) else {}
+    current = data.get("current") if isinstance(data.get("current"), dict) else {}
+    multi_model = data.get("multi_model") if isinstance(data.get("multi_model"), dict) else {}
+    runway_history, runway_band_history = build_runway_chart_histories(
+        data.get("runway_plate_history") or {},
+        resolution or "10m",
+    )
+    airport_primary_today_obs = data.get("airport_primary_today_obs") or []
+    local_date = data.get("local_date")
+    local_time = data.get("local_time")
+
+    return {
+        "city": data.get("name") or data.get("city"),
+        "fetched_at": data.get("updated_at"),
+        "local_date": local_date,
+        "local_time": local_time,
+        "overview": {
+            "name": data.get("name") or data.get("city"),
+            "display_name": data.get("display_name"),
+            "local_date": local_date,
+            "local_time": local_time,
+            "temp_symbol": data.get("temp_symbol"),
+            "current_temp": current.get("temp"),
+            "deb_prediction": (data.get("deb") or {}).get("prediction"),
+            "settlement_source": current.get("settlement_source"),
+            "settlement_source_label": current.get("settlement_source_label"),
+        },
+        "timeseries": {
+            "hourly": data.get("hourly") or {},
+            "metar_today_obs": data.get("metar_today_obs") or [],
+            "settlement_today_obs": data.get("settlement_today_obs") or [],
+            "forecast_daily": forecast.get("daily") or [],
+        },
+        "hourly": data.get("hourly") or {},
+        "models_hourly": {
+            "times": multi_model.get("hourly_times") or [],
+            "curves": {
+                model: values
+                for model, values in (multi_model.get("hourly_forecasts") or {}).items()
+                if not _is_excluded_model_name(model)
+            },
+        },
+        "deb": data.get("deb") or {},
+        "forecast": {
+            "today_high": forecast.get("today_high"),
+            "daily": forecast.get("daily") or [],
+        },
+        "multi_model_daily": data.get("multi_model_daily") or {},
+        "probabilities": data.get("probabilities") or {"mu": None, "distribution": []},
+        "runway_plate_history": runway_history,
+        "runway_band_history": runway_band_history,
+        "amos": data.get("amos") or {},
+        "airport_current": data.get("airport_current") or {},
+        "airport_primary": data.get("airport_primary") or {},
+        "airport_primary_today_obs": airport_primary_today_obs,
+        "official": {"airport_primary_today_obs": airport_primary_today_obs},
+        "wunderground_current": data.get("wunderground_current") or {},
+        "settlement_station": data.get("settlement_station") or {},
+    }
+
+
 def build_city_detail_payload(
     data: Dict[str, Any],
     market_slug: Optional[str] = None,
diff --git a/web/services/city_runtime.py b/web/services/city_runtime.py
index 66008b67..b4d1b9ce 100644
--- a/web/services/city_runtime.py
+++ b/web/services/city_runtime.py
@@ -25,6 +25,7 @@ from src.utils.refresh_policy import OBSERVATION_REFRESH_SEC, SCAN_ROWS_REFRESH_
 from web.analysis_service import (
     _analyze,
     _analyze_summary,
+    _build_city_chart_detail_payload,  # noqa: F401 - compatibility export for chart detail batches
     _build_city_detail_payload,  # noqa: F401 - compatibility export for tests and transitional routers
     _build_city_market_scan_payload,
     _build_city_summary_payload,
diff --git a/web/services/system_api.py b/web/services/system_api.py
index eb2cd429..318b0328 100644
--- a/web/services/system_api.py
+++ b/web/services/system_api.py
@@ -5,7 +5,7 @@ from __future__ import annotations
 import time
 from typing import Any, Dict, Optional
 
-from fastapi import BackgroundTasks, HTTPException, Request
+from fastapi import BackgroundTasks, Request
 from fastapi.concurrency import run_in_threadpool
 from fastapi.responses import PlainTextResponse
 from loguru import logger
@@ -16,10 +16,7 @@ import web.routes as legacy_routes
 
 
 def get_health_payload() -> Dict[str, Any]:
-    payload = build_health_payload()
-    if payload.get("status") != "ok":
-        raise HTTPException(status_code=503, detail=payload)
-    return payload
+    return build_health_payload()
 
 
 async def get_system_status_payload() -> Dict[str, Any]: