Fix auto-install.sh to work standalone, not just baked into the image

Two real bugs, both hit live:

1. Shebang: #!/run/current-system/sw/bin/bash only resolves on an
   already-activated NixOS system -- running the checked-out script
   directly (e.g. from a stock ISO, cloned repo) failed with "cannot
   execute: required file not found" on a non-NixOS box. Switched to
   #!/usr/bin/env bash, which resolves identically on NixOS
   (environment.usrbinenv's own default) and any normal Linux distro.
   Also fixed the file's missing executable bit.

2. FLAKE_BASE_URL: previously depended on pkgs.replaceVars substituting
   a Nix-templated @lanDomain@ placeholder at build time -- meaning it
   only ever worked when baked into the built installer image, not when
   run straight from a checkout (the literal, unexpanded "@lanDomain@"
   string reached git as a bogus hostname). Replaced with LAN_DOMAIN in
   scripts/env.sh (manually kept in sync with variables.nix's lanDomain,
   same pattern as NIX_CACHE_HOST/nixCacheHost already), sourced by the
   script itself like every other script in scripts/. Dropped
   pkgs.replaceVars from modules/installer/common.nix entirely --
   scripts/env.sh is now baked into the image alongside auto-install.sh
   at a matching relative path (/etc/nixos-installer/env.sh next to
   /etc/nixos-installer/installer/auto-install.sh) so the script's own
   relative `source` line resolves the same way in both contexts.

loginShellInit's invocation path and docs/auto-installer.md updated to
match. Verified: shellcheck clean on both scripts, the baked files are
byte-identical to their checked-in sources (no templating left to
verify), and codex-maintenance.sh (secret grep, fmt, statix, full eval
of every host/package including the installer/pxe artifacts) passes
clean.

CLAUDE.md

@@ -179,13 +179,24 @@ instead of copying it.
 - `scripts/installer/auto-install.sh` — the interactive install script
   baked into the auto-installer image (see `docs/auto-installer.md`), kept
   as a real, version-controlled shell file rather than inline in
-  `modules/installer/common.nix`'s Nix. `common.nix` wires it in with
-  `pkgs.replaceVars ../../scripts/installer/auto-install.sh { inherit (vars) lanDomain; }`,
-  substituting the single `@lanDomain@` placeholder from `variables.nix` —
-  every other `${...}` in the script is a literal bash reference,
-  untouched by this. `replaceVars` fails the build if any `@name@`-shaped
-  placeholder is left unsubstituted, so a typo'd or renamed variable is
-  caught at eval time rather than silently shipping broken.
+  `modules/installer/common.nix`'s Nix. It sources `scripts/env.sh` itself
+  for `LAN_DOMAIN` (`export LAN_DOMAIN`/`: "${LAN_DOMAIN:=...}"`, matching
+  `variables.nix`'s `lanDomain` — manually kept in sync, same pattern as
+  `NIX_CACHE_HOST` mirroring `nixCacheHost`), rather than Nix-level string
+  substitution — that's what makes it work identically whether run
+  straight from a git checkout or from inside the built installer image.
+  `common.nix` bakes `scripts/env.sh` in alongside it at a matching
+  relative path (`/etc/nixos-installer/env.sh` next to
+  `/etc/nixos-installer/installer/auto-install.sh`) so the script's own
+  `source "$(dirname ...)/../env.sh"` line resolves the same way in both
+  contexts — this is also why it's invoked from
+  `/etc/nixos-installer/installer/auto-install.sh` rather than a flat
+  `/etc/auto-install.sh`. `#!/usr/bin/env bash`, not
+  `#!/run/current-system/sw/bin/bash`: the latter only resolves on an
+  already-activated NixOS system, breaking the checked-out-file case
+  entirely (confirmed live: "cannot execute: required file not found" on
+  a non-NixOS box); `/usr/bin/env` is reliably present on both NixOS
+  (`environment.usrbinenv`'s own default) and any normal Linux distro.
 
 ### `scripts/secrets/`
 
@@ -297,8 +308,9 @@ Sourced by the scripts above, never run directly:
 ### Top level
 
 - `scripts/env.sh` — shared config (`PROXMOX_HOST`, storage pool, bridge,
-  default cores/memory) sourced by `create-proxmox-resource.sh`. Add new
-  cross-script config here instead of duplicating it per-script.
+  default cores/memory, `NIX_CACHE_HOST`, `LAN_DOMAIN`) sourced by
+  `create-proxmox-resource.sh` and `scripts/installer/auto-install.sh`. Add
+  new cross-script config here instead of duplicating it per-script.
 - `scripts/bump-nixpkgs-release.sh` — bumps `flake.nix`'s `nixpkgs.url`/
   `home-manager.url` in place. Exists because flake input URLs can't
   reference `variables.nix` (confirmed empirically — `nix flake metadata`

docs/auto-installer.md

@@ -8,10 +8,13 @@ lives here.
 The installer provides a small NixOS install environment (ISO, or the same
 image netbooted via PXE) with SSH access, Git support, and an interactive
 installation script.
-Logging in as any user (root or `nixos`) runs `/etc/auto-install.sh`,
-discovers available hosts from this same flake, lets the operator choose a
-target, applies that host's Disko storage configuration, installs NixOS, and
-reboots.
+Logging in as any user (root or `nixos`) runs
+`/etc/nixos-installer/installer/auto-install.sh` (the same file as
+`scripts/installer/auto-install.sh` in this repo — see "Installer process"
+below for why it's baked in at that path rather than a flat
+`/etc/auto-install.sh`), discovers available hosts from this same flake,
+lets the operator choose a target, applies that host's Disko storage
+configuration, installs NixOS, and reboots.
 
 **This applies to every `nixosConfigurations` target except `lxc-*` hosts —
 see "LXC hosts" immediately below for why those are different.**
@@ -217,7 +220,21 @@ entirely (see "LXC hosts" above), so it never reaches this code path.
 
 ## Installer process
 
-`/etc/auto-install.sh`:
+`scripts/installer/auto-install.sh` is a real, version-controlled shell
+script — not an inline Nix string. It sources `scripts/env.sh` for
+`LAN_DOMAIN` itself (same as every other script in `scripts/`), so it
+behaves identically whether it's run straight from a git checkout (e.g.
+manually, from a stock NixOS ISO that isn't this repo's own installer
+image) or from inside the built installer image. That's also why it's
+baked in at `/etc/nixos-installer/installer/auto-install.sh` rather than a
+flat `/etc/auto-install.sh` — `modules/installer/common.nix` bakes
+`scripts/env.sh` in alongside it at `/etc/nixos-installer/env.sh`,
+preserving the same relative layout (`installer/auto-install.sh` ->
+`../env.sh`) the checked-out repo has, so the script's own
+`source ".../env.sh"` line resolves correctly in both places without any
+Nix-level templating.
+
+Once running, it:
 
 1. Queries `nixosConfigurations` from this flake over the network (`git+https://<lanDomain>/beatzaplenty/nixos.git`) — this happens at *install* time, not build time, so a generic installer image always sees whatever hosts are currently committed, without needing a rebuild.
 2. Presents them as a menu; confirms the choice.

modules/installer/common.nix

@@ -46,18 +46,22 @@
     ];
 
     # Auto-install script, kept as a real, version-controlled shell file at
-    # scripts/installer/auto-install.sh rather than an inline Nix string --
-    # replaceVars only substitutes the one value (lanDomain) that genuinely
-    # needs to come from variables.nix; every other "@..." pattern in the
-    # script is a literal `${...}` bash reference, untouched by this.
-    etc."auto-install.sh" = {
-      source = pkgs.replaceVars ../../scripts/installer/auto-install.sh {
-        inherit (vars) lanDomain;
-      };
+    # scripts/installer/auto-install.sh rather than an inline Nix string.
+    # It sources scripts/env.sh itself (for LAN_DOMAIN, same as every other
+    # script in this repo) rather than relying on Nix-level templating, so
+    # it behaves identically whether it's run straight from a git checkout
+    # or from here -- baking scripts/env.sh in alongside it at a matching
+    # relative path (installer/auto-install.sh -> ../env.sh) is what makes
+    # that resolve correctly in both places.
+    etc = {
+      "nixos-installer/env.sh".source = ../../scripts/env.sh;
 
+      "nixos-installer/installer/auto-install.sh" = {
+        source = ../../scripts/installer/auto-install.sh;
         mode = "0755";
       };
     };
+  };
 
   programs.git.enable = true;
 
@@ -69,7 +73,7 @@
   # file-copying/chown.
   programs.bash.loginShellInit = ''
     if [ -n "$PS1" ] && [ ! -e "$HOME/.auto_install_ran" ]; then
-      sudo /etc/auto-install.sh
+      sudo /etc/nixos-installer/installer/auto-install.sh
       touch "$HOME/.auto_install_ran"
     fi
   '';

scripts/env.sh

@@ -82,6 +82,12 @@ export PVE1_HOST PVE_TEST_HOST PROXMOX_HOST PROXMOX_SSH_USER PROXMOX_STORAGE \
 : "${NIX_CACHE_HOST:=nix-cache}"
 export NIX_CACHE_HOST
 
+# Matches variables.nix's lanDomain (the Gitea host this flake's own repo
+# is served from -- see scripts/installer/auto-install.sh's FLAKE_BASE_URL)
+# -- update both if it ever changes.
+: "${LAN_DOMAIN:=gitea.lan.ddnsgeek.com}"
+export LAN_DOMAIN
+
 # nix_extra_opts: call as a plain statement (NOT inside $(...)/<(...) --
 # that forks a subshell, and the whole point is exporting a decision back
 # into *this* shell) to populate the global NIX_OPTS array with whatever

scripts/installer/auto-install.sh

@@ -1,9 +1,12 @@
-#!/run/current-system/sw/bin/bash
+#!/usr/bin/env bash
 set -eux
 
 set -euo pipefail
 
-export FLAKE_BASE_URL="git+https://@lanDomain@/beatzaplenty/nixos.git"
+# shellcheck source=../env.sh
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)/env.sh"
+
+export FLAKE_BASE_URL="git+https://${LAN_DOMAIN}/beatzaplenty/nixos.git"
 
 echo "Fetching available NixOS hosts from flake..."
 # Two categories deliberately excluded from the menu: