  We extend the covering of even and odd Khovanov link homology to tangles,
using arc algebras. For this, we develop the theory of quasi-associative
algebras and bimodules graded over a category with a 3-cocycle. Furthermore, we
show that a covering version of a level 2 cyclotomic half 2-Kac--Moody algebra
acts on the bicategory of quasi-associative bimodules over the covering arc
algebras, relating our work to a construction of Vaz.
