perf: bound Today readiness latency (#441)

frontend/service-worker.js

@@ -1,6 +1,6 @@
 const BASE = new URL('./', self.location.href).pathname;
 importScripts(BASE + 'static/background-issue-sync.js');
-const CACHE = 'stackchain-dashboard-shell-v73';
+const CACHE = 'stackchain-dashboard-shell-v74';
 const OFFLINE_LEASE_URL = new URL(BASE + '__offline-session-lease', self.location.origin).href;
 const OUTAGE_STATUSES = new Set([500, 502, 503, 504]);
 const NAVIGATION_TIMEOUT_MS = self.__STACKCHAIN_NAVIGATION_TIMEOUT_MS || 4000;

frontend/today-readiness.js

@@ -32,15 +32,19 @@
       const candidates = preferredIndex >= 0
         ? ordered.slice(preferredIndex).concat(ordered.slice(0, preferredIndex))
         : [preferred].concat(ordered);
-      const states = [];
-      for (const item of candidates) states.push({ item, ...(await classify(item)) });
+      const targetState = { item:preferred, ...(await classify(preferred)) };
       if (request !== generation) return 'superseded';
-      const targetState = states[0];
       if (targetState.status === 'ready') {
         pending = null;
         onOpen(action, preferred);
         return 'opened';
       }
+      const fallbackStates = await Promise.all(candidates.slice(1).map(async item => ({
+        item,
+        ...(await classify(item)),
+      })));
+      const states = [targetState, ...fallbackStates];
+      if (request !== generation) return 'superseded';
       const nextReadyState = states.slice(1).find(state => state.status === 'ready');
       pending = {
         action,