I see, sleepy me didn't find anything you didn't think of before^^

Suggestion for the problem with staying open after a number of flips:
maybe it's possible to get the amount of gas needed to compress the springs again estimated (or tested). thus you can try to build a digital manometer in, and only allow flipping when you got more than a certain amount of pressure (and gas) left, maybe except you press an "override" button for desperate needs? I don't know much about pneumatics (the little i know comes from softair guns a few years ago, so...), but if there is a good way to do this, it could be an option.
Gas needed will vary by temperature, so measuring pressure could be more reliable than just counting flips.
From one of my softair the range for how long a tank of gas works is from "barely the 20 rounds in the magazin" when firing fast up to "no problem shooting three magazins in a row if every shot is taken with care"