docs: correct statements that no longer match the configuration

Assisted-by: DeepSeek Harness 0.2.1-rc.2 (claude-opus-5-5)

nixos-installer/Justfile

@@ -2,7 +2,7 @@
 default:
     @just --list
 
-# Enter a shell session which has all the necessary tools for this flake
+# Build the ai host's system closure to check this flake
 [linux]
 test:
   nix build ".#nixosConfigurations.ai.config.system.build.toplevel" --show-trace --verbose

nixos-installer/README.md

@@ -84,6 +84,10 @@ nixos-enter
 #   mv /etc/ssh /persistent/etc/
 # Then exit and:
 exit
+# keep this checkout (still in nix-config/nixos-installer); / is tmpfs, so put it where
+# preservation mounts ~/nix-config from
+mkdir -p /mnt/persistent/home/ryan
+cp -r .. /mnt/persistent/home/ryan/nix-config
 umount -R /mnt
 reboot
 ```
@@ -115,7 +119,6 @@ After the first boot:
 3. Deploy the main config:
 
    ```bash
-   sudo mv /etc/nixos ~/nix-config
    sudo chown -R ryan:ryan ~/nix-config
    cd ~/nix-config
    just niri

nixos-installer/README.shoukei.md

@@ -236,7 +236,7 @@ Then, generate the NixOS configuration:
 nixos-generate-config --root /mnt
 
 # we need to update our filesystem configs in old hardware-configuration.nix according to the generated one.
-cp /etc/nixos/hardware-configuration.nix ./nix-config/hosts/12kingdoms-shoukei/hardware-configuration-new.nix
+cp /mnt/etc/nixos/hardware-configuration.nix ./nix-config/hosts/12kingdoms-shoukei/hardware-configuration-new.nix
 vim ./nix-config
 ```
 
@@ -278,7 +278,7 @@ mv /etc/ssh /persistent/etc/
 exit
 
 # delete the generated configuration after editing
-rm -f /mnt/etc/nixos
+rm -rf /mnt/etc/nixos
 rm ~/nix-config/hosts/12kingdoms-shoukei/hardware-configuration-new.nix
 
 # NOTE: `cat README.shoukei.md | grep git-1 > git-1.sh` to generate this script
@@ -287,8 +287,10 @@ git config --global user.email "ryan4yin@linux.com"   # git-1
 git config --global user.name "Ryan Yin"              # git-1
 git commit -am "feat: update hardware-configuration"
 
-# copy our configuration to the installed file system
-cp -r ~/nix-config /mnt/etc/nixos
+# copy our configuration to the installed file system; / is tmpfs there, so put it where
+# preservation mounts ~/nix-config from
+mkdir -p /mnt/persistent/home/ryan
+cp -r ~/nix-config /mnt/persistent/home/ryan/nix-config
 
 # sync the disk, unmount the partitions, and close the encrypted device
 sync
@@ -319,7 +321,6 @@ decrypt them automatically on the new host when I deploy my NixOS configuration.
 After all these steps, we can finally deploy the main flake's NixOS configuration by:
 
 ```bash
-sudo mv /etc/nixos ~/nix-config
 sudo chown -R ryan:ryan ~/nix-config
 
 cd ~/nix-config