Send heartbeats from the provider. This keeps unauthorized and offline devices present as well, which is what we want. This also greatly reduces the number of queries to rethinkdb.

lib/roles/provider.js

@@ -362,6 +362,19 @@ module.exports = function(options) {
     lifecycle.share('Tracker', tracker)
   })
 
+  // This keeps the devices "present" in the database. It relies on the
+  // provider channel changing on every run so that we never match old
+  // devices.
+  ;(function heartbeat() {
+    push.send([
+      wireutil.heartbeat
+    , wireutil.envelope(new wire.ProviderHeartbeatMessage(
+        solo
+      ))
+    ])
+    setTimeout(heartbeat, options.heartbeatInterval)
+  })()
+
   lifecycle.observe(function() {
     clearTimeout(totalsTimer)