Reduce terminal detail refresh traffic

frontend/components/dashboard/scan-terminal/__tests__/proxyCachePolicy.test.ts

@@ -20,6 +20,7 @@ export function runTests() {
   const cached = buildCityDetailProxyCachePolicy("false", 15);
   assert.equal(cached.fetchMode, "revalidate");
   assert.equal(cached.revalidateSeconds, 15);
+  assert.match(cached.responseCacheControl, /max-age=15/);
   assert.match(cached.responseCacheControl, /s-maxage=15/);
 
   const scanForced = buildForceRefreshProxyCachePolicy("true", 10);

frontend/components/dashboard/scan-terminal/__tests__/refreshCadencePolicy.test.ts

@@ -76,6 +76,12 @@ export async function runTests() {
       chartSource.includes("setHourly(data)"),
     "visible chart fallback must refresh the full city detail payload at the current chart resolution when SSE patches stop",
   );
+  assert(
+    chartLogicSource.includes("HOURLY_FORCE_REFRESH_DEDUP_MS") &&
+      chartLogicSource.includes("maxAgeMs: HOURLY_FORCE_REFRESH_DEDUP_MS") &&
+      chartLogicSource.includes("recentlyRefreshed.data"),
+    "forced chart detail refreshes should reuse a very recent full-detail payload instead of refetching repeatedly",
+  );
   assert(
     __shouldPollLiveChartForTest({ city: "shanghai", compact: true, isActive: false, isMaximized: false }) === true,
     "compact grid slots are visible charts and should run the no-patch fallback guard",

frontend/components/dashboard/scan-terminal/temperature-chart-logic.ts

@@ -353,6 +353,7 @@ type LocalDayBounds = { start: number; end: number };
 
 const MAX_OBS_POINTS = 1440;
 const HOURLY_CACHE_TTL_MS = DASHBOARD_REFRESH_POLICY_MS.metar;
+const HOURLY_FORCE_REFRESH_DEDUP_MS = 60_000;
 const _hourlyCache = new Map<string, { ts: number; data: HourlyForecast }>();
 const _hourlyRequestCache = new Map<string, Promise<HourlyForecast>>();
 const MAX_HOURLY_DETAIL_CONCURRENT_REQUESTS = 3;
@@ -366,13 +367,16 @@ const SESSION_CACHE_TTL_MS = DASHBOARD_REFRESH_POLICY_MS.metar;
 
 type HourlyCacheEntry = { ts: number; data: HourlyForecast };
 
-function isFreshHourlyCacheEntry(entry: HourlyCacheEntry | null | undefined) {
+function isFreshHourlyCacheEntry(
-  return Boolean(entry && Date.now() - Number(entry.ts || 0) < SESSION_CACHE_TTL_MS);
+  entry: HourlyCacheEntry | null | undefined,
+  maxAgeMs = SESSION_CACHE_TTL_MS,
+) {
+  return Boolean(entry && Date.now() - Number(entry.ts || 0) < maxAgeMs);
 }
 
 function readSessionCache(
   city: string,
-  options: { allowStale?: boolean } = {},
+  options: { allowStale?: boolean; maxAgeMs?: number } = {},
 ): HourlyCacheEntry | null {
   if (typeof window === "undefined") return null;
   try {
@@ -382,7 +386,7 @@ function readSessionCache(
     if (
       item &&
       item.ts &&
-      (options.allowStale || Date.now() - item.ts < SESSION_CACHE_TTL_MS)
+      (options.allowStale || Date.now() - item.ts < (options.maxAgeMs ?? SESSION_CACHE_TTL_MS))
     ) {
       return item;
     }
@@ -392,10 +396,10 @@ function readSessionCache(
 
 function readHourlyCacheEntry(
   cacheKey: string,
-  options: { allowStale?: boolean } = {},
+  options: { allowStale?: boolean; maxAgeMs?: number } = {},
 ): HourlyCacheEntry | null {
   const cached = _hourlyCache.get(cacheKey);
-  if (cached && (options.allowStale || isFreshHourlyCacheEntry(cached))) {
+  if (cached && (options.allowStale || isFreshHourlyCacheEntry(cached, options.maxAgeMs))) {
     return cached;
   }
 
@@ -1193,6 +1197,13 @@ async function fetchHourlyForecastForCity(
     if (cached) {
       return cached.data;
     }
+  } else {
+    const recentlyRefreshed = readHourlyCacheEntry(cacheKey, {
+      maxAgeMs: HOURLY_FORCE_REFRESH_DEDUP_MS,
+    });
+    if (recentlyRefreshed) {
+      return recentlyRefreshed.data;
+    }
   }
 
   const requestKey = options.ignoreCache ? `${city}:${resParam}:live` : `${city}:${resParam}`;
@@ -2459,6 +2470,7 @@ export {
   MAX_HOURLY_DETAIL_CONCURRENT_REQUESTS,
   HOURLY_DETAIL_REQUEST_TIMEOUT_MS,
   HOURLY_CACHE_TTL_MS,
+  HOURLY_FORCE_REFRESH_DEDUP_MS,
   _hourlyCache,
   __readHourlyCacheEntryForTest,
   resolveCityDetailFromBatch as __resolveCityDetailFromBatchForTest,

frontend/lib/proxy-cache-policy.ts

@@ -28,4 +28,22 @@ export function buildForceRefreshProxyCachePolicy(
   };
 }
 
-export const buildCityDetailProxyCachePolicy = buildForceRefreshProxyCachePolicy;
+export function buildCityDetailProxyCachePolicy(
+  forceRefresh: string | null | undefined,
+  revalidateSeconds = 15,
+): ProxyCachePolicy {
+  if (isForceRefreshValue(forceRefresh)) {
+    return {
+      fetchMode: "no-store",
+      responseCacheControl: "no-store, max-age=0",
+    };
+  }
+  return {
+    fetchMode: "revalidate",
+    responseCacheControl: `public, max-age=${revalidateSeconds}, s-maxage=${revalidateSeconds}, stale-while-revalidate=${Math.max(
+      revalidateSeconds * 3,
+      30,
+    )}`,
+    revalidateSeconds,
+  };
+}