It is better to add snapshot of dev-lang/mujs and use it in app-text/mupdf.
Created attachment 575986 [details, diff] Patch
I'm not convinced that it's better. Upstream might deem this snapshot ready for a release of mupdf, but if they don't bother making a 1.0.6 release, it might mean that they don't deem it ready for other revdeps. I prefer using the bundled mupdf until 1.0.6 is released.