installer-iso: force script stage 1 — systemd initrd has no findiso

terra booted the staged installer this time but dropped to an emergency
shell: stage 1 mounted /sysroot, then timed out on /sysroot/nix/.ro-store
waiting for /dev/disk/by-label/nixos-minimal-26.05-x86_64.

findiso= is handled only in the scripted stage-1-init.sh, which loop-mounts
the file the param points at and symlinks it to /dev/root. The systemd initrd
— the default since 26.05 — has no findiso handling at all: iso-image.nix
mounts /iso directly from /dev/disk/by-label/<volumeID>, a label that only
exists when the ISO is the physical boot medium. Booted as kernel + initrd
off the ESP with the iso as a plain file on another partition, that label
never appears, so the store squashfs never mounts.

The entire `install <config> localhost` path is built on findiso, so pin the
installer to script stage 1. Verified: /iso device flips to /dev/root,
root=LABEL=... is added to the params, the rebuilt initrd's /init is
stage-1-init.sh and carries the findiso logic.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CLAUDE.md

@@ -145,6 +145,15 @@ kept its ssh host key. Run it after ANY change to the kexec paths.
   rather than `--print-boot-path` in that mode. `homelab-auto-install.service` deletes
   the leftover NVRAM entry as soon as it boots; both it and the script match the label
   `Homelab Installer` EXACTLY (a prefix match would delete the Windows or Limine entry).
+- **`installer-iso` must force `boot.initrd.systemd.enable = false`.** `findiso=` is a
+  SCRIPT-stage-1 feature (`stage-1-init.sh` loop-mounts the file it points at and
+  symlinks it to `/dev/root`). The systemd initrd — default since 26.05 — has NO findiso
+  path: it mounts `/iso` straight from `/dev/disk/by-label/<volumeID>` (iso-image.nix),
+  a label that only exists when the ISO is the physical boot medium. EFI-stub-booted off
+  the ESP with the iso as a plain file on another fs, that label never appears; stage 1
+  mounts `/sysroot` fine, then times out on `/sysroot/nix/.ro-store` waiting for
+  `/dev/disk/by-label/nixos-minimal-…` and drops to an emergency shell. The whole
+  `install <config> localhost` findiso path depends on script stage 1.
 - **The staging-dir guard must fail CLOSED, and `findmnt` needs `--nofsroot`**: on btrfs
   `findmnt -no SOURCE` prints `/dev/sdb2[/@]`, which `lsblk` cannot open, so a naive
   parent-device lookup comes back empty. Treating empty as "different disk" silently

flake.nix

@@ -208,6 +208,19 @@
               networking.hostName = "homelab-installer";
               environment.systemPackages = [ pkgs.git ];
 
+              # findiso= is a SCRIPT-stage-1 feature (stage-1-init.sh) only. The
+              # systemd initrd — the default since 26.05 — has no findiso path
+              # at all: it mounts /iso straight from
+              # /dev/disk/by-label/<volumeID> (iso-image.nix), which only exists
+              # when the ISO is the physical boot medium. Booted as a kernel +
+              # initrd off the ESP with the iso as a plain file elsewhere, that
+              # label never appears and stage 1 times out into an emergency
+              # shell (mounts /sysroot fine, then fails /sysroot/nix/.ro-store).
+              # Script stage 1 instead loop-mounts the file findiso= points at
+              # and symlinks it to /dev/root — which is the whole mechanism this
+              # install path relies on. So force it off here.
+              boot.initrd.systemd.enable = false;
+
               # installation-cd-minimal leaves experimental-features unset, so
               # the ISO's nix.conf has no `nix-command`/`flakes` at all (unlike
               # the nixos-images kexec installer, which sets