code: @TaskAction
    public void startAction() throws AppEngineException, IOException {
  
      // Add a listener to write to a file for non-blocking starts, this really only works
      // when the gradle daemon is running (which is default for newer versions of gradle)
      File logFile = new File(devAppServerLoggingDir, "dev_appserver.out");
      FileOutputLineListener logFileWriter = new FileOutputLineListener(logFile);
  
      Logger taskLogger = getLogger();
      ProcessHandler processHandler =
          LegacyProcessHandler.builder()
              .addStdOutLineListener(taskLogger::lifecycle)
              .addStdOutLineListener(logFileWriter)
              .addStdErrLineListener(taskLogger::lifecycle)
              .addStdErrLineListener(logFileWriter)
              .setExitListener(new NonZeroExceptionExitListener())
              .buildDevAppServerAsync(runConfig.getStartSuccessTimeout());
  
      devServers.newDevAppServer(processHandler).run(runConfig.toRunConfiguration());
  
      getLogger().lifecycle("Dev App Server output written to : " + logFile.getAbsolutePath());
    }
docs: Task entrypoint : start the dev appserver (non-blocking).