Offline nixos-install still built from source: the drvs that embed the
user's hostname/username/UUIDs (etc, initrd, toplevel, HM activation)
must be REBUILT, and their builders need tools outside every runtime
closure (etc → python3-minimal, initrd → packing tools). Pin each drv's
inputDerivation into the ISO — the standard nixos-test offline trick.
Also: with no network every substituter query is a DNS retry storm that
ends in a nix goal.cc assertion crash (core dump observed); the installer
now probes connectivity and disables substituters when offline, both on
the live system and inside the nixos-enter HM pre-activation.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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