src/Tools/jEdit/src/session_build.scala

           case exn: Throwable =>
             (Output.error_text(Exn.message(exn)) + "\n", Exn.return_code(exn, 2))
         }
 
       progress.echo(out + (if (rc == 0) "OK\n" else "Return code: " + rc + "\n"))
+
       if (rc == 0) Isabelle_Logic.session_start()
+      else progress.echo("Build failed -- prover remains inactive!")
 
       return_code(rc)
     }
   }
 }