Thanks for fixing G3.
I like out of the box solutions and that includes my D8 solution :P The exponential nature of the level makes it very attractive for unrolling, nothing wrong with that :P Especially because its just one level where it even is viable in the first place, and considering the cost tradeoff it will never affect the normal solutions.
If larger test cases are added, it will first of all start lagging the game quite hard and secondly, it will still always be more optimal to hardcode the bottom layers and add a proper iterative algorithm ontop of this. You could restrict the number of workers but this will invalidate a large potion of current solutions aswell as add significant difficulty for future players, and it will just bloat the root score instead if that option will be available.
Another alternative would be to just hard limit the cost but that would be quite lame. Overall I think you should just come to terms with the solution considering that it only really affects this level.
If the cost graph is the problem, why not make it logarithmic (for this level only maybe considering the exponential nature) and/or implementing a graph break?
This is less about technicalities (the threshold is already excluded, so it doesn't affect other players' scores or graphs), and more about the concept that solutions work in the general case. If you need to change your algorithm whenever new test cases are added, then I don't consider it a valid solution, and I'll work to improve the test cases until it is invalidated.
Brute-forcing is actually the easiest one for me - it's evident from the graphs and doesn't require a "prove or disprove" process (recall that I handle players' solutions as black boxes). And D8 is not special in this respect, previous cases that I've invalidated included a solution that assumed out-degree <= 5 or so (I'm sure that it was out of the box...)
Note that this approach doesn't preclude loop unrolling as an optimization strategy. The game does favor minimal and elegant solutions (that's why cost is calculated as it is, and why certain achievements exist), but score is determined equally as a function of cost and cycles (i.e. commutatively).