While running:

  guix pull -q --commit=0ff72d105

on two different machines, we found that the resulting derivation would
be different.  The “right one” (same as on ci.guix is):

--8<---------------cut here---------------start------------->8---
$ readlink $(readlink  my.0ff72d105)
/gnu/store/1g1zhh3864xzh0csqrzf5c1qkbd3q5pp-profile
$ guix gc --derivers $(readlink -f my.0ff72d105)
/gnu/store/b6zvsh8z7fmx5bpw21wqhnl82kfag5s1-profile.drv
$ guix gc -R $(guix gc --derivers $(readlink -f my.0ff72d105)) |grep guix-0ff72d105
/gnu/store/sarff52m9zavyyadllixk9brjqfacn57-guix-0ff72d105-modules-builder
/gnu/store/ys9rcn7d9xp4d2wwcy6i21gm6rmviv31-guix-0ff72d105-builder
/gnu/store/6l3xi9lcib99lpdq6z7x5bahm4ppxw45-guix-0ff72d105-modules.drv
/gnu/store/w3h8kvag0dbw9y6qq35r3fb87b1xpykd-guix-0ff72d105.drv
--8<---------------cut here---------------end--------------->8---

On the other machine, where substitutes would consequently be
unavailable, we’d get:

--8<---------------cut here---------------start------------->8---
$ readlink fernando.0ff72d105.drv
/gnu/store/hl1di1dq6mcd7jl0phk5bi12yqcc9dif-guix-0ff72d105.drv
$ guix gc -R /gnu/store/hl1di1dq6mcd7jl0phk5bi12yqcc9dif-guix-0ff72d105.drv |grep guix-0ff72d105
/gnu/store/p04znrg5frzj6gpiafpx7cgr4n7jly5s-guix-0ff72d105-modules-builder
/gnu/store/sc7y5i9pi5w2cpba0xmk7pzqckn642bp-guix-0ff72d105-modules.drv
/gnu/store/p4bh6x0r8qy9lpg77p52cjzxjzhp0mwr-guix-0ff72d105-builder
/gnu/store/hl1di1dq6mcd7jl0phk5bi12yqcc9dif-guix-0ff72d105.drv
--8<---------------cut here---------------end--------------->8---

Digging into the derivation graph reveals the difference below in the
derivation that builds the grafted avahi: