Andreas Enge <andreas@enge.fr> skribis:

>  385: 2 [process-stderr #]
>  170: 1 [read-string #<input-output: socket 5>]
> In unknown file:
>    ?: 0 [utf8->string #vu8(115 97 109 112 108 101 95 114 97 116 101 95 105 

That’s because the build log contains a non-UTF-8 sequence, and
store.scm expects UTF-8 (for no good reason).

The attached patch removes that UTF-8 assumption.  Can you test whether
it fixes the problem?