Unless you think otherwise - what, exactly, is the Constitutional error?
Appeals of charging decisions are not limited to only constitutional errors, as you term them.
“...there are two clear situations in which it is inappropriate for a prosecutor to bring charges: (1) when such prosecution is unfair or biased and (2) when it is vindictive. A third possible situation is when the charging decision is in disregard of legislative intent...”
These are reasons that have existing associated case law.
“Vindictive” sounds like the most likely grounds to me.
And there’s nothing to preclude a NOVEL application of defendents’ rights in this case either... is there? Because the overarching conclusion is that a charging decision IS appealable. For several reasons already in common law, and maybe others as well. Contrary to what you have been touting.