Well, as I said, you are asking for something we don’t have at the moment, and something that’s not easy to add to the firmware. So either you use the features available to accommodate your need, or just throw away OpenSprinkler and find a product that fits your need. Look, if the feature was easy to add, we would have added it already, don’t you think?
Regardless, I think you are refusing to make creative use of features already available to address your need. For example, if you can’t let each zone run for a short amount of time and switch to another zone, you can create one program per zone. Have that program run just one zone, and use ‘repeat’ to break it into small sessions so if power is reset it loses just one small session. Because the entire program has only one zone, it will just continuously run that zone until it finishes all repeats. Create another program for the next zone and start at the appropriate time. There are creative ways to get what you need. But it seems you would rather want to complain about what’s missing than to leverage what’s already there to address your need.
And I don’t understand why UPS is not viable solution. I am not talking about a big box UPS — it can be as small as a USB power bank. Only the controller itself needs to be powered, not your solenoids. No matter how small your box is, I can’t imagine why it wouldn’t fit essentially a cell phone battery in it.
I have never hard of this definition of ‘fail-safe’ as you described.
Lastly, again, why not choose another product? If every other product has this essential feature you want, why spending so much time here complaining about OpenSprinkler? Don’t you want to find a product that does what you want, and move on?