Crystallinity for reduced syntomic cohomology and the mod $(p,v_1^{p^{n-2}})$ $K$-theory of $\mathbb{Z}/p^{n}$

We prove that the functor taking an animated ring $R$ to its mod $(p,v_1^{p^n})$ derived syntomic cohomology factors through the functor $R \mapsto R/p^{n+2}$. We then use this to completely and explicitly compute the mod $(p,v_1 ^{p^{n}})$ syntomic cohomology of $\mathbb{Z}/p^{k}$ whenever $k \geq n+2$.