src/Tools/VSCode/src/server.scala

           {
             progress.echo(fail_msg); error(fail_msg)
           }
         }
 
-        val session_base = Sessions.session_base(options, session_name, session_dirs)
+        val session_base =
+          Sessions.session_base(options, session_name, dirs = session_dirs, all_known = true)
         val resources = new VSCode_Resources(options, session_base, log)
           {
             override def commit(change: Session.Change): Unit =
               if (change.deps_changed || undefined_blobs(change.version.nodes).nonEmpty)
                 delay_load.invoke()