feat: add GPS status endpoint and dashboard indicator

- add /api/gps/status for thread/fix-age visibility
- surface GPS status in Pi health and live GPS cards
- add tests for app_gps status snapshots

Co-authored-by: Copilot <[email protected]>

static/js/yaris.js

@@ -209,6 +209,59 @@ function reverseGeocode(lat, lon) {
         .catch(() => { clearTimeout(t); _geocodePending = false; el.textContent = fallback; });
 }
 
+function formatGpsAge(seconds) {
+    if (seconds == null) return 'No fix yet.';
+    if (seconds < 10) return 'Last fix just now.';
+    if (seconds < 60) return `Last fix ${Math.round(seconds)}s ago.`;
+    const mins = Math.floor(seconds / 60);
+    const secs = Math.round(seconds % 60);
+    return secs ? `Last fix ${mins}m ${secs}s ago.` : `Last fix ${mins}m ago.`;
+}
+
+function renderGpsStatus(status) {
+    const liveBadge = document.getElementById('gps-live-badge');
+    const fixDetail = document.getElementById('gps-fix-detail');
+    const healthStatus = document.getElementById('pi-gps-status');
+    const healthDetail = document.getElementById('pi-gps-detail');
+    if (!liveBadge || !fixDetail || !healthStatus || !healthDetail) return;
+
+    let label = 'Unavailable';
+    let badgeClass = 'text-bg-secondary';
+    let detail = 'GPS thread has not started.';
+
+    if (status.thread_alive) {
+        if (status.has_fix) {
+            const stale = status.fix_age_seconds != null && status.fix_age_seconds > 30;
+            label = stale ? 'Stale fix' : 'Live fix';
+            badgeClass = stale ? 'text-bg-warning' : 'text-bg-success';
+            detail = formatGpsAge(status.fix_age_seconds);
+        } else {
+            label = 'No fix';
+            badgeClass = 'text-bg-warning';
+            detail = 'GNSS thread is running, but no fix is available yet.';
+        }
+    } else {
+        label = 'Offline';
+        badgeClass = 'text-bg-danger';
+    }
+
+    liveBadge.className = `badge ${badgeClass}`;
+    liveBadge.textContent = label;
+    fixDetail.textContent = detail;
+    healthStatus.textContent = label;
+    healthStatus.className = `h6 fw-bold mb-0 ${label === 'Live fix' ? 'text-success' : label === 'Offline' ? 'text-danger' : 'text-warning'}`;
+    healthDetail.textContent = detail;
+}
+
+async function refreshGpsStatus() {
+    const response = await fetch('/api/gps/status');
+    const status = await response.json();
+    if (!response.ok) {
+        throw new Error(status.error || 'Could not load GPS status.');
+    }
+    renderGpsStatus(status);
+}
+
 socket.on('gps_location', function(data) {
     const LocationX = document.getElementById('gpsLocationX');
     const LocationY = document.getElementById('gpsLocationY');
@@ -218,6 +271,7 @@ socket.on('gps_location', function(data) {
     const lat = parseFloat(data[0]);
     const lon = parseFloat(data[1]);
     if (lat != null && lon != null) {
+        renderGpsStatus({thread_alive: true, has_fix: true, fix_age_seconds: 0});
         if (!map.hasLayer(mapTiles)) {
             mapTiles.addTo(map);
         }
@@ -334,3 +388,19 @@ window.setInterval(function () {
         message.hidden = false;
     });
 }, 30000);
+
+refreshGpsStatus().catch(function (error) {
+    renderGpsStatus({thread_alive: false, has_fix: false, fix_age_seconds: null});
+    const fixDetail = document.getElementById('gps-fix-detail');
+    const healthDetail = document.getElementById('pi-gps-detail');
+    if (fixDetail) fixDetail.textContent = error.message;
+    if (healthDetail) healthDetail.textContent = error.message;
+});
+window.setInterval(function () {
+    refreshGpsStatus().catch(function (error) {
+        const fixDetail = document.getElementById('gps-fix-detail');
+        const healthDetail = document.getElementById('pi-gps-detail');
+        if (fixDetail) fixDetail.textContent = error.message;
+        if (healthDetail) healthDetail.textContent = error.message;
+    });
+}, 15000);