location-first scan: geolocation prompt decides the scan (8s fallback to plain scan, never blocks); server 'location upgrade' rule re-alerts with map link when coords arrive after a no-loc alert

frontend/internal/handlers/scan.go

@@ -162,11 +162,13 @@ func (a *App) shouldAlert(ctx context.Context, tag db.Tag, scan db.Scan, hasLoc
 
 	// Within the window?
 	if time.Since(last.ScannedAt.Time) < alertWindow {
-		// Re-alert on movement >250 m, or a different finder phone.
+		// Re-alert on movement >250 m, a different finder phone, or a location
+		// upgrade (previous alert had no coords — send the map link).
 		moved := hasLoc && last.Lat.Valid && last.Lng.Valid &&
 			sms.HaversineMeters(last.Lat.Float64, last.Lng.Float64, *lat, *lng) > alertMinDistance
+		locationUpgrade := hasLoc && !last.Lat.Valid
 		differentPhone := phone != "" && phone != last.ScannerPhone.String
-		return moved || differentPhone, ""
+		return moved || locationUpgrade || differentPhone, ""
 	}
 	return true, ""
 }

frontend/templates/tag-public.html

@@ -142,12 +142,12 @@
             function () {
               sendScan(null, null); // no location — page still works, button stays
             },
-            {timeout: 20000, maximumAge: 0}
+            {timeout: 8000, maximumAge: 0}
           );
         }
-        // Fire a scan immediately so a tag view always reports (and alerts) —
+        // Location-first: send coords when the finder approves. If the prompt is
-        // location is an upgrade, never a gate.
+        // denied, unsupported, or silently blocked (8s), fall back to a plain scan
-        sendScan(null, null);
+        // so every tag view still reports.
         if (btn) btn.addEventListener("click", tryLocation);
         tryLocation();
       })();