Optimal paths with varying target gradients

Hi, my name is Gaku

I need some help to get the optimal paths with varying target gradients.

Now I design the slope on the mountain.

And I want to make it under the  1:12 gradients (this is good for people to walk).

So I need the program of grasshopper for "path finding" on the certain surface which change the curve following the defined "max gradient".

I couldn't find programs which have the parameter "max gradient".

So please help me to show the someone's programs or tell me how to make.

And please let me know which add-on should I use.

Thanks