Limit city detail fallback to batch failures

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

@@ -118,6 +118,12 @@ export async function runTests() {
       flushCityDetailBatchBlock.includes("payload?.partial === true"),
     "partial detail-batch misses should resolve without immediately issuing single-city fallback requests",
   );
+  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",
+  );
   const fetchHourlyBlock = chartLogicSource.match(/async function fetchHourlyForecastForCity[\s\S]*?\r?\n}\r?\n\r?\nfunction fetchCityDetailWithTimeout/)?.[0] || "";
   assert(
     fetchHourlyBlock.includes("queueCityDetailBatch(city, resParam)") &&

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

@@ -1118,6 +1118,11 @@ async function flushCityDetailBatch(resolution: string) {
 
   try {
     const payload = await fetchCityDetailBatchWithTimeout(cities, resolution);
+    if (!payload) {
+      await resolveCityDetailBatchWithSingleFallback(cities, queue, resolution);
+      return;
+    }
+
     const details = payload?.details || {};
     const partialMissingCities =
       payload?.partial === true
@@ -1136,33 +1141,35 @@ async function flushCityDetailBatch(resolution: string) {
           resolveBatchWaiters(waiters, null);
           return;
         }
-        try {
-          resolveBatchWaiters(
-            waiters,
-            await runQueuedHourlyDetailRequest(() => fetchSingleHourlyForecastForCity(city, resolution)),
-          );
-        } catch (error) {
-          rejectBatchWaiters(waiters, error);
-        }
+        resolveBatchWaiters(waiters, null);
       }),
     );
   } catch (error) {
-    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 || error);
-        }
-      }),
-    );
+    await resolveCityDetailBatchWithSingleFallback(cities, queue, resolution, error);
   }
 }
 
+async function resolveCityDetailBatchWithSingleFallback(
+  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);
+      }
+    }),
+  );
+}
+
 function fetchCityDetailBatchWithTimeout(cities: string[], resolution: string) {
   const controller = new AbortController();
   const timeoutId = globalThis.setTimeout(() => controller.abort(), HOURLY_DETAIL_REQUEST_TIMEOUT_MS);