nixos-install builds with --store /mnt and passes its own substituter as
"auto?trusted=1", which in that context resolves to the target store
itself — so nothing flowed from the ISO and nix fell back to a
full-source bootstrap (gcc/python/bash tarball fetches → offline death).
Host-store simulation (fresh local?root, substituters cleared) proves
"daemon?trusted=1" makes the whole install substitute + build offline:
1125 paths copied, only the per-machine config drvs built locally.
Also drop --offline from the chroot HM build (that flag disables ALL
substituters; plain empty substituters does what we want without it).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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