Actually, here is a clue:

> ./pre-inst-env guix build --check next-gtk-webkit
The following graft will be made:
   /gnu/store/jgb5j3pg45kf19n7cgw1j5kjagzmbqg1-next-gtk-webkit-1.1.0.drv
applying 2 grafts for /gnu/store/jgb5j3pg45kf19n7cgw1j5kjagzmbqg1-next-gtk-webkit-1.1.0.drv...
grafting '/gnu/store/8llinghxcslyxmvszjlvlxbv411vra0x-next-gtk-webkit-1.1.0' -> '/gnu/store/ildn4l2wr0y7irm2536dnp88hhrdphsz-next-gtk-webkit-1.1.0'...
/gnu/store/ildn4l2wr0y7irm2536dnp88hhrdphsz-next-gtk-webkit-1.1.0

So it's a grafting issue, probably caused by a dependency.

- How can I know which dependency causes the graft?

- Why isn't grafting taken into account by `guix size` and `guix pack`?

- Is `guix pack --no-grafts` the way to go?  Well, I'll try that...

-- 
Pierre Neidhardt
https://ambrevar.xyz/