Hi Julien,

> When [invoke's child return status] is correct, [invoke] returns #<unspecified>, so we need to explicitly return #t.

That's not true.  invoke returns #t in the successful case--I designed it that way mostly to get rid of the many vestigal #t's in phases.

(I hope that in a future version of guix, the necessity of using #t to end phases will be gone entirely)