Scale SSE replay window by visible cities

frontend/README.md

@@ -192,7 +192,7 @@ Ops：
 - 支付相关路由：`no-store`
 - 当 detail 缓存只返回单模型或单日 forecast 时，前端会自动强刷完整 detail，并在补齐前显示同步提示 / 占位卡
 - 今日日内分析打开时如果正在切换城市、日期或 detail 深度，弹窗会阻断旧内容点击并显示刷新锁
-- 终端图表订阅 `/api/events?cities=...&since_revision=...&replay_limit=500`，接收 `city_observation_patch.v1`；无 patch 超过 2 分钟时，可见图表才触发 60 秒兜底刷新
+- 终端图表订阅 `/api/events?cities=...&since_revision=...&replay_limit=按可见城市数动态限制`，接收 `city_observation_patch.v1`；无 patch 超过 2 分钟时，可见图表才触发 60 秒兜底刷新
 - 前端只消费 HTTP snapshot + SSE patch，不直接感知 Redis；Redis Stream / SQLite event log 都由后端统一封装
 
 ## Vercel 节流建议

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

@@ -94,6 +94,13 @@ export function runTests() {
   assert(hook.includes("subscribedCities"), "frontend patch hook must track the visible city subscription set");
   assert(hook.includes("since_revision"), "frontend patch hook must reconnect with since_revision");
   assert(hook.includes("resync_required"), "frontend patch hook must react to server resync_required events");
+  assert(
+    hook.includes("SSE_REPLAY_EVENTS_PER_CITY") &&
+      hook.includes("resolveSseReplayLimit") &&
+      hook.includes('params.set("replay_limit", String(resolveSseReplayLimit(cities.length)))') &&
+      !hook.includes('params.set("replay_limit", "500")'),
+    "frontend patch hook should size SSE replay_limit by visible city count instead of always asking for 500 events",
+  );
   assert(hook.includes("lastRevision"), "frontend patch hook must track the global last processed revision");
   assert(hook.includes("Map<"), "frontend patch hook must keep latest patches in a Map");
   assert(hook.includes("useLatestPatch"), "frontend patch hook must export useLatestPatch(city)");

frontend/hooks/use-sse-patches.ts

@@ -5,6 +5,9 @@ import { resolveBackendApiUrl } from "@/lib/backend-api";
 
 const V1_EVENT_TYPE = "city_observation_patch.v1";
 const SSE_SUBSCRIPTION_RECONNECT_DELAY_MS = 150;
+const SSE_REPLAY_BASE_LIMIT = 60;
+const SSE_REPLAY_EVENTS_PER_CITY = 24;
+const SSE_REPLAY_MAX_LIMIT = 240;
 
 export type CityPatch = {
   type?: string;
@@ -91,12 +94,17 @@ function buildSseUrl(baseUrl: string) {
   if (lastRevision > 0) {
     params.set("since_revision", String(lastRevision));
   }
-  params.set("replay_limit", "500");
+  params.set("replay_limit", String(resolveSseReplayLimit(cities.length)));
 
   const query = params.toString();
   return query ? `${baseUrl}?${query}` : baseUrl;
 }
 
+function resolveSseReplayLimit(cityCount: number) {
+  const requested = Math.max(1, cityCount) * SSE_REPLAY_EVENTS_PER_CITY;
+  return Math.max(SSE_REPLAY_BASE_LIMIT, Math.min(SSE_REPLAY_MAX_LIMIT, requested));
+}
+
 function currentConnectionKey() {
   return `${useFallbackUrl ? "fallback" : "direct"}:${subscribedCityList().join("|")}:${lastRevision}`;
 }