Maximum Total from Optimal Activation Order

You are given two integer arrays energy and threshold, each of length n.
Initially, all reactors are inactive. You can activate them in any order, but under specific conditions:
• To activate a reactor at index i, the number of currently active reactors must be strictly less than threshold[i].
• When you activate reactor i, it contributes energy[i] to your total energy output.
• After each activation, if the number of currently active reactors becomes x, then all reactors j where threshold[j] <= x become permanently inactive, even if they are currently active.
Your task is to determine the maximum total energy that can be achieved through an optimal activation sequence.