Alert history: say what each alert is for, where, and when

- Plain-language meaning for common NWS products, shown in the row and expanded view
- Details column: reason, area, severity, effective window; click for full text/instructions
- New alerts log area, severity, urgency, certainty and sender
- Older entries are filled in from NWS by alert id (cached in data/alert-details.json);
  alerts NWS no longer serves fall back to the built-in meaning

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app/server.js

@@ -190,6 +190,13 @@ function recordAlertLog(entry) {
   }
 }
 
+// Fields worth keeping from an NWS alert so the history can say what it was for and where
+function nwsLogFields(p) {
+  return { event: p.event, headline: p.headline, description: p.description, instruction: p.instruction,
+    areaDesc: p.areaDesc, severity: p.severity, urgency: p.urgency, certainty: p.certainty, senderName: p.senderName,
+    effective: p.effective, expires: p.expires };
+}
+
 // Tracks NWS alert IDs already written this process lifetime to avoid duplicate log lines
 // across multiple subscribers covering the same geographic alert.
 const loggedAlertIds = new Set();
@@ -530,7 +537,7 @@ try {
   else rebuildRecordsFromFiles();
 } catch (e) { console.error('[records] startup rebuild error:', e.message); }
 setInterval(saveRecordsStore, 30 * 1000).unref();
-for (const sig of ['SIGTERM', 'SIGINT']) process.on(sig, () => { saveRecordsStore(); process.exit(0); });
+for (const sig of ['SIGTERM', 'SIGINT']) process.on(sig, () => { saveRecordsStore(); try { saveAlertDetails(); } catch {} process.exit(0); });
 
 function loadStationReadings(rangeMs) {
   const now = Date.now();
@@ -1254,7 +1261,7 @@ async function alertWatcherCron() {
       if (alertId && !loggedAlertIds.has(alertId)) {
         loggedAlertIds.add(alertId);
         const p = a.properties || {};
-        recordAlertLog({ type: 'nws', alertId, event: p.event, headline: p.headline, description: p.description, instruction: p.instruction, effective: p.effective, expires: p.expires, lat: dashLat, lon: dashLon });
+        recordAlertLog({ type: 'nws', alertId, ...nwsLogFields(p), lat: dashLat, lon: dashLon });
       }
     }
   }
@@ -1280,7 +1287,7 @@ async function alertWatcherCron() {
           const alertId = a.id || p.id;
           if (alertId && !loggedAlertIds.has(alertId)) {
             loggedAlertIds.add(alertId);
-            recordAlertLog({ type: 'nws', alertId, event: p.event, headline: p.headline, description: p.description, instruction: p.instruction, effective: p.effective, expires: p.expires, lat: sub.lat, lon: sub.lon });
+            recordAlertLog({ type: 'nws', alertId, ...nwsLogFields(p), lat: sub.lat, lon: sub.lon });
           }
         }
         sub.seenAlertIds = [...new Set([...sub.seenAlertIds, ...newAlerts.map(f => f.id || f.properties?.id)])].slice(-200);
@@ -2056,6 +2063,51 @@ app.get('/api/station/trend', requireDashboardAuth, (_req, res) => {
 });
 
 // Alert history log
+// ── NWS alert details (looked up by alert id, cached on disk) ────────────────
+const ALERT_DETAIL_FILE = path.join(DATA_DIR, 'alert-details.json');
+let alertDetails = {};
+try { alertDetails = JSON.parse(fs.readFileSync(ALERT_DETAIL_FILE, 'utf8')); } catch {}
+let alertDetailsDirty = false;
+function saveAlertDetails() {
+  if (!alertDetailsDirty) return;
+  try { fs.writeFileSync(ALERT_DETAIL_FILE + '.tmp', JSON.stringify(alertDetails)); fs.renameSync(ALERT_DETAIL_FILE + '.tmp', ALERT_DETAIL_FILE); alertDetailsDirty = false; }
+  catch (e) { console.error('[alerts] detail cache save error:', e.message); }
+}
+setInterval(saveAlertDetails, 30 * 1000).unref();
+
+const ALERT_ID_RE = /^https:\/\/api\.weather\.gov\/alerts\/[A-Za-z0-9:._-]+$/;
+const alertLookupsInFlight = new Map();
+async function lookupAlertDetail(id) {
+  const hit = alertDetails[id];
+  if (hit && !hit.unavailable) return hit;
+  if (hit && hit.unavailable && Date.now() - hit.at < 6 * 3600000) return hit; // don't hammer NWS for gone alerts
+  if (alertLookupsInFlight.has(id)) return alertLookupsInFlight.get(id);
+  const job = (async () => {
+    try {
+      const r = await fetchWithRetry(id, { attempts: 1, timeoutMs: 10000, fetchOptions: { headers: { 'User-Agent': 'weather-app-v2 (nate@necloud.us)', Accept: 'application/geo+json' } } });
+      const f = await r.json();
+      const p = f.properties || f;
+      if (!p.event) throw new Error('no event');
+      alertDetails[id] = { ...nwsLogFields(p), fetchedAt: Date.now() };
+    } catch (e) {
+      alertDetails[id] = { unavailable: true, at: Date.now() };
+    }
+    alertDetailsDirty = true;
+    alertLookupsInFlight.delete(id);
+    return alertDetails[id];
+  })();
+  alertLookupsInFlight.set(id, job);
+  return job;
+}
+
+app.get('/api/dashboard/alert-detail', requireDashboardAuth, async (req, res) => {
+  const id = String(req.query.id || '');
+  if (!ALERT_ID_RE.test(id)) return res.status(400).json({ error: 'Invalid alert id' });
+  const d = await lookupAlertDetail(id);
+  if (d.unavailable) return res.status(404).json({ error: 'NWS no longer provides this alert' });
+  res.json(d);
+});
+
 app.get('/api/dashboard/alert-history', requireDashboardAuth, (req, res) => {
   const days = Math.min(90, Math.max(1, parseInt(req.query.days) || 30));
   const results = [];
@@ -2071,6 +2123,12 @@ app.get('/api/dashboard/alert-history', requireDashboardAuth, (req, res) => {
       }
     } catch {}
   }
+  // Fill in text/area for older entries from the detail cache when we have it
+  for (const e of results) {
+    if (e.type !== 'nws' || e.description || !e.alertId) continue;
+    const d = alertDetails[e.alertId];
+    if (d && !d.unavailable) Object.assign(e, Object.fromEntries(Object.entries(d).filter(([k, v]) => v != null && e[k] == null)));
+  }
   results.sort((a, b) => b.ts - a.ts);
   res.json(results);
 });