Advertise muc#stable_id feature

xmpp/handlers.go

@@ -572,6 +572,7 @@ func handleGetDisco(dt discoType, s xmpp.Sender, iq *stanza.IQ) {
 							"muc_unmoderated",
 							"muc_nonanonymous",
 							"muc_unsecured",
+							"http://jabber.org/protocol/muc#stable_id",
 						)
 						fields := []*stanza.Field{
 							&stanza.Field{
@@ -594,7 +595,10 @@ func handleGetDisco(dt discoType, s xmpp.Sender, iq *stanza.IQ) {
 						disco.Form = stanza.NewForm(fields, "result")
 					}
 				} else {
-					disco.AddFeatures(stanza.NSDiscoItems)
+					disco.AddFeatures(
+						stanza.NSDiscoItems,
+						"http://jabber.org/protocol/muc#stable_id",
+					)
 					disco.AddIdentity("Telegram group chats", "conference", "text")
 				}
 			}