Right now, AFAIK, 'mach build' does not automatically store a build log. I'm guessing it's similar for other mach commands. I know it has a '-l' option but it has to be invoked manually. Since space is cheap and time is not, it would make sense IMO to always automatically store the last mach run log - for 'build' and also for other commands. Possibly also rotate the last 10 or NN logs in case several attempts are made. It could output the logs to ./logs dir, for instance.