src/Pure/Tools/build_cluster.scala

     init()
     _init.foreach(_.join)
 
     _workers =
       for (session <- _sessions) yield {
-        Future.thread(session.host.message("run")) {
-          Exn.release(capture(session.host, "run") { session.start() })
+        Future.thread(session.host.message("work")) {
+          Exn.release(capture(session.host, "work") { session.start() })
         }
       }
   }
 
   override def join: List[Build_Cluster.Result] = synchronized {