‘inferior-eval-with-store’ swallows build output. Namely, the ‘proxy’ procedure proxies interactions between the daemon and the inferior, without any interpretation. Thus, the inferior gets to see build output, which it may or may not display, depending on its ‘current-build-output-port’ binding, but the calling process itself doesn’t see anything.
This is similar to <https://issues.guix.gnu.org/41930>. To fix it would require either interpreting all the protocol as messages are forwarded, or having another socket to forward build output from the inferior to the caller. (Another option might be to install a “build handler” in the inferior, but older Guixes didn’t have that.) Note that this issue is normally quite rare. The one case where it happens is when calling ‘inferior-package-derivation’ on a package where grafts potentially apply; in this case, the inferior starts building the ungrafted variant of the package, and it’s that build output that’s swallowed. Ludo’.
