We cannot support dynamic hashInvalidation.
This means the invalidation can change *after* or *before* a 'vars generate'
But not during the generation itself. This causes heavy performance overhead.
Additionally this introduces a fixed-point-iteration (compare: fixed-point-iteration vs. fixed-point-function)
This iteration takes ~ 1min for two bare-bones machine with 1 generator (see: checks/data-mesher)
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