fix(proxmox): embed SSH host key via NIXOS_HOST_KEYS_DIR so sops can decrypt on first boot

--pre-format-files placed the key on the QEMU builder VM's rootfs, not the
target disk. nixos-install chroots into the target and runs sshd-keygen, which
found no key in the chroot and generated a fresh (unregistered) one. sops then
could not decrypt on first boot because the key didn't match .sops.yaml, leaving
both root and nixos with '!' in /etc/shadow even after mutableUsers = false was
set (hashedPasswordFile pointed to paths sops never wrote).

Fix modules/platforms/proxmox.nix to embed the clan SSH host key in
environment.etc via NIXOS_HOST_KEYS_DIR at eval time -- the same pattern
lxc.nix uses. nixos-install's own activation places the key on the target disk,
sshd-keygen finds it already present and skips generation, and sops decrypts
correctly on first boot. Includes the same preserveSshHostKey/restoreSshHostKey
activation scripts as lxc.nix so subsequent nixos-rebuild switch calls (without
NIXOS_HOST_KEYS_DIR) don't remove the key as "obsolete" from environment.etc.

Update create-proxmox-resource.sh: switch VM builds from
  ./result-<target> --pre-format-files ... --build-memory 2048
to
  NIXOS_HOST_KEYS_DIR=$(pwd)/host-keys nix build --impure ... diskoImagesScript
  ./result-<target> --build-memory 2048
matching the LXC build path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011uRcikkTp3D5VbXj2DwNpQ

modules/platforms/proxmox.nix

@@ -1,9 +1,81 @@
-{ ... }:
+{ lib, flakeTarget, ... }:
 
+let
+  # Bakes this exact flake target's pre-generated SSH host key straight
+  # into /etc/ssh/ -- mirrors lxc.nix's builtins.getEnv pattern (impure
+  # and empty under normal `nix build`/`nix eval`, so this is a no-op
+  # unless explicitly opted into with NIXOS_HOST_KEYS_DIR=... --impure).
+  #
+  # Unlike --pre-format-files (which places files on the QEMU builder VM's
+  # rootfs, not the target disk), embedding via environment.etc here means
+  # nixos-install's own activation step installs the key onto the target
+  # disk. sshd-keygen then finds it already present and skips generation,
+  # so the disk image boots with the clan-registered key and sops can
+  # decrypt on first boot.
+  #
+  # Without this, nixos-install's sshd-keygen activation generates a fresh
+  # key (unregistered in .sops.yaml), sops decryption fails permanently,
+  # and password hashes are never applied -- confirmed live: passwords
+  # stayed '!' even with mutableUsers = false because hashedPasswordFile
+  # pointed to a path that sops never wrote.
+  hostKeysDirStr = builtins.getEnv "NIXOS_HOST_KEYS_DIR";
+  hasHostKeysDir = hostKeysDirStr != "" && builtins.pathExists hostKeysDirStr;
+  hostKeysDir = /. + hostKeysDirStr;
+
+  privKeyFile = hostKeysDir + "/${flakeTarget}_ssh_host_ed25519_key";
+  pubKeyFile = hostKeysDir + "/${flakeTarget}_ssh_host_ed25519_key.pub";
+  hasKeyForThisTarget =
+    hasHostKeysDir
+    && builtins.pathExists privKeyFile
+    && builtins.pathExists pubKeyFile;
+in
 {
   imports = [
     ../hardware-configuration/vm/proxmox.nix
     ../boot/efi.nix
     ../disko/proxmox.nix
   ];
+
+  environment.etc = lib.mkIf hasKeyForThisTarget {
+    "ssh/ssh_host_ed25519_key" = {
+      source = privKeyFile;
+      mode = "0600";
+    };
+    "ssh/ssh_host_ed25519_key.pub" = {
+      source = pubKeyFile;
+      mode = "0644";
+    };
+  };
+
+  # NixOS's etc activation removes any /etc file that was in the previous
+  # generation's environment.etc but is absent from the current one. Since
+  # the SSH key is only in environment.etc during the --impure build (when
+  # NIXOS_HOST_KEYS_DIR is set), normal rebuilds would remove it as
+  # "obsolete". These scripts mirror lxc.nix's approach: save the live key
+  # before etc runs, restore it after. Without the explicit deps, the
+  # topological sort places preserveSshHostKey after etc (confirmed live on
+  # lxc-tor-relay: position 7 vs etc's position 5), so the key is gone
+  # before it can be saved.
+  system.activationScripts = {
+    preserveSshHostKey = ''
+      if [ -f /etc/ssh/ssh_host_ed25519_key ]; then
+        cp /etc/ssh/ssh_host_ed25519_key /run/sshd-host-key-preserve.tmp
+        cp /etc/ssh/ssh_host_ed25519_key.pub /run/sshd-host-key-preserve.pub.tmp
+      fi
+    '';
+
+    restoreSshHostKey = {
+      deps = [ "etc" ];
+      text = ''
+        if [ ! -f /etc/ssh/ssh_host_ed25519_key ] && [ -f /run/sshd-host-key-preserve.tmp ]; then
+          install -m 0600 /run/sshd-host-key-preserve.tmp /etc/ssh/ssh_host_ed25519_key
+          install -m 0644 /run/sshd-host-key-preserve.pub.tmp /etc/ssh/ssh_host_ed25519_key.pub
+        fi
+        rm -f /run/sshd-host-key-preserve.tmp /run/sshd-host-key-preserve.pub.tmp
+      '';
+    };
+
+    etc = { deps = [ "preserveSshHostKey" ]; };
+    setupSecrets = { deps = [ "restoreSshHostKey" ]; };
+  };
 }

scripts/proxmox/create-proxmox-resource.sh

@@ -354,6 +354,14 @@ fi
 # feeds straight into the guest's real hostname) disagree with host.nix.
 [[ -z "$name" ]] && name="$host"
 
+# For VM builds: the diskoImagesScript (run via QEMU on the node) writes the
+# raw disk image as <hostname>.raw into the CWD it was called from (the remote
+# repo dir), not to /var/lib/vz/import/ or anywhere else.  Import directly from
+# there -- no intermediate mv that can fail crossing filesystem boundaries or
+# leave a stale file on error.
+vm_built_raw=""
+[[ "$type" == "vm" ]] && vm_built_raw="${remote_repo_dir}/${host}.raw"
+
 # --- refuse to duplicate a host that's already live on the node ---------
 # Queries the node itself (qm/pct's own name/hostname config), not any
 # static list in this repo -- a file can't track whether a resource still
@@ -688,10 +696,14 @@ if [[ -n "$image" ]]; then
 elif [[ "$force_rebuild" -eq 1 ]]; then
   echo "--force-rebuild: skipping the existing-image check on ${node}."
 else
-  echo "==> Checking whether ${node} already has ${remote_path}..."
+  # VMs: check for the raw image in the remote repo dir (where disko writes it).
+  # LXC: check for the tarball in iso_storage (where the LXC build stages it).
+  _check_path="$remote_path"
+  [[ "$type" == "vm" ]] && _check_path="$vm_built_raw"
+  echo "==> Checking whether ${node} already has ${_check_path}..."
   if [[ "$dry_run" -eq 1 ]]; then
-    echo "[dry-run] would check: ssh ${ssh_target} -- test -f ${remote_path}"
+    echo "[dry-run] would check: ssh ${ssh_target} -- test -f ${_check_path}"
-  elif ssh "$ssh_target" "test -f '${remote_path}'" 2>/dev/null; then
+  elif ssh "$ssh_target" "test -f '${_check_path}'" 2>/dev/null; then
     echo "Found it -- reusing, skipping build (use --force-rebuild to override)."
     image_already_remote=1
   else
@@ -766,23 +778,29 @@ REMOTE_SCRIPT
     fi
   else
     if [[ "$dry_run" -eq 1 ]]; then
-      echo "[dry-run] would build on ${node}: nix build --no-use-registries --no-accept-flake-config${nix_opts_display} \\"
+      echo "[dry-run] would build on ${node}: NIXOS_HOST_KEYS_DIR=\$(pwd)/host-keys nix build --impure --no-use-registries --no-accept-flake-config${nix_opts_display} \\"
       echo "[dry-run]   .#nixosConfigurations.${flake_target}.config.system.build.diskoImagesScript"
-      echo "[dry-run] would run:   ${sudo_display}./result-${flake_target} \\"
+      echo "[dry-run] would run:   ${sudo_display}./result-${flake_target} --build-memory 2048"
-      echo "[dry-run]                --pre-format-files host-keys/${flake_target}_ssh_host_ed25519_key /etc/ssh/ssh_host_ed25519_key \\"
+      echo "[dry-run] image will be at ${vm_built_raw} (imported from there; no mv to /var/lib/vz/import/)"
-      echo "[dry-run]                --pre-format-files host-keys/${flake_target}_ssh_host_ed25519_key.pub /etc/ssh/ssh_host_ed25519_key.pub \\"
-      echo "[dry-run]                --build-memory 2048"
-      echo "[dry-run] would stage the result at ${remote_path}"
       local_image="<built-image>.raw"
     else
       echo "==> Building Disko image for ${flake_target} on ${node}..."
       # See the LXC branch above for why this is one %q-quoted command
       # string rather than separate ssh argv elements.
-      printf -v remote_cmd 'bash -s -- %q %q %q %q %q %q' \
+      # $7 = image_name (hostname, the diskoImagesScript's own output filename).
-        "$remote_repo_dir" "$flake_target" "$remote_dir" "$remote_filename" "$NIX_EXTRA_OPTS" "$sudo_prefix"
+      #
+      # NIXOS_HOST_KEYS_DIR + --impure: modules/platforms/proxmox.nix reads
+      # this env var at eval time (like lxc.nix) to embed the clan SSH host
+      # key in environment.etc. nixos-install's own activation then places the
+      # key on the target disk, so sshd-keygen finds it already present and
+      # skips generation. --pre-format-files put the key on the QEMU builder
+      # VM's rootfs (not the target disk), so sshd-keygen regenerated a fresh
+      # key -- one not registered in .sops.yaml -- and sops could never decrypt.
+      printf -v remote_cmd 'bash -s -- %q %q %q %q %q %q %q' \
+        "$remote_repo_dir" "$flake_target" "$remote_dir" "$remote_filename" "$NIX_EXTRA_OPTS" "$sudo_prefix" "$host"
       ssh "$ssh_target" "$remote_cmd" <<'REMOTE_SCRIPT'
 set -euo pipefail
-repo_dir="$1"; target="$2"; dest_dir="$3"; dest_name="$4"; nix_extra_opts_str="$5"; sudo_pfx="$6"
+repo_dir="$1"; target="$2"; dest_dir="$3"; dest_name="$4"; nix_extra_opts_str="$5"; sudo_pfx="$6"; image_name="$7"
 declare -a NIX_OPTS=()
 [[ -n "$nix_extra_opts_str" ]] && eval "NIX_OPTS=(${nix_extra_opts_str})"
 cd "$repo_dir"
@@ -794,24 +812,26 @@ if [[ ! -f "host-keys/${target}_ssh_host_ed25519_key" ]]; then
   echo "and ensure it was synced here before starting the build." >&2
   exit 1
 fi
-nix build --no-use-registries --no-accept-flake-config "${NIX_OPTS[@]}" \
+# Build diskoImagesScript with NIXOS_HOST_KEYS_DIR so proxmox.nix embeds the
+# clan SSH key in environment.etc (same as lxc.nix). This causes nixos-install
+# to place the key on the target disk, so sshd-keygen finds it and skips
+# generation -- the disk image boots with the registered key, sops decrypts.
+NIXOS_HOST_KEYS_DIR="$(pwd)/host-keys" nix build --impure \
+  --no-use-registries --no-accept-flake-config "${NIX_OPTS[@]}" \
   ".#nixosConfigurations.${target}.config.system.build.diskoImagesScript" \
   --out-link "result-${target}"
-$sudo_pfx "./result-${target}" \
+# Remove any stale .raw from a previous failed build so the post-build check
-  --pre-format-files "$(pwd)/host-keys/${target}_ssh_host_ed25519_key" /etc/ssh/ssh_host_ed25519_key \
+# below is unambiguous (diskoImagesScript writes to CWD as ${image_name}.raw).
-  --pre-format-files "$(pwd)/host-keys/${target}_ssh_host_ed25519_key.pub" /etc/ssh/ssh_host_ed25519_key.pub \
+$sudo_pfx rm -f "${image_name}.raw" 2>/dev/null || true
-  --build-memory 2048
+$sudo_pfx "./result-${target}" --build-memory 2048
-built="$(find . -maxdepth 1 -name '*.raw' -newer "result-${target}" | head -1)"
+if [[ ! -f "${image_name}.raw" ]]; then
-if [[ -z "$built" ]]; then
+  echo "ERROR: ${image_name}.raw not found in ${repo_dir} after build -- disko/QEMU may have failed." >&2
-  echo "ERROR: no .raw image found in ${repo_dir} after build." >&2
   exit 1
 fi
-$sudo_pfx mkdir -p "$dest_dir"
+echo "Built image: ${repo_dir}/${image_name}.raw"
-$sudo_pfx mv "$built" "${dest_dir}/${dest_name}"
-echo "Built and staged: ${dest_dir}/${dest_name}"
 REMOTE_SCRIPT
-      local_image="$remote_path"
+      local_image="$vm_built_raw"
-      echo "Built on ${node}: ${remote_path}"
+      echo "Built on ${node}: ${vm_built_raw}"
     fi
   fi
 fi
@@ -889,14 +909,35 @@ else
 --net0 virtio,bridge=${bridge} --bios ovmf --machine q35 --scsihw virtio-scsi-pci \
 --efidisk0 ${storage}:1,efitype=4m,pre-enrolled-keys=0 --agent enabled=1"
 
+  # VMs built on the node: import from the repo dir (where disko/QEMU wrote it).
+  # VMs from --image: import from remote_path (where scp uploaded it).
+  _import_path="${remote_path}"
+  [[ -z "$image" ]] && _import_path="${vm_built_raw}"
   if [[ "$dry_run" -eq 1 ]]; then
-    echo "[dry-run] ssh ${ssh_target} -- ${sudo_display}qm importdisk ${vmid} ${remote_path} ${storage}"
+    echo "[dry-run] ssh ${ssh_target} -- ${sudo_display}qm importdisk ${vmid} ${_import_path} ${storage}"
     echo "[dry-run] (would parse the resulting disk identifier from that output)"
     echo "[dry-run] ssh ${ssh_target} -- ${sudo_display}qm set ${vmid} --scsi0 ${storage}:<parsed-disk-id>"
   else
-    importdisk_output="$(ssh "$ssh_target" "${sudo_prefix} qm importdisk ${vmid} ${remote_path} ${storage}")"
+    if ! importdisk_output="$(ssh "$ssh_target" "${sudo_prefix} qm importdisk ${vmid} ${_import_path} ${storage}" 2>&1)"; then
+      echo "ERROR: qm importdisk failed:" >&2
+      echo "${importdisk_output}" >&2
+      exit 1
+    fi
     echo "$importdisk_output"
-    disk_id="$(echo "$importdisk_output" | grep -oP "(?<=Successfully imported disk as ')[^']+" | sed 's/^unused[0-9]*://')"
+    # PVE output format: "unusedN: successfully imported disk '<storage>:<vol>'"
+    # (lowercase "successfully", no "as"; the primary regex targets this form; the
+    # || true inside the substitution prevents set -e from aborting when grep finds
+    # no match -- without it the script would silently exit before reaching the
+    # fallback whenever the PVE format doesn't match).
+    disk_id="$(echo "$importdisk_output" | grep -oP "successfully imported disk '\\K[^']+" || true)"
+    if [[ -z "$disk_id" ]]; then
+      # Fallback for other PVE output variants: read qm config directly.
+      unused_line="$(ssh "$ssh_target" "${sudo_prefix} qm config ${vmid}" | grep '^unused[0-9]*:' | head -1 || true)"
+      if [[ -n "$unused_line" ]]; then
+        disk_id="${unused_line#*: }"
+        echo "Note: disk ID resolved from qm config: ${disk_id}"
+      fi
+    fi
     if [[ -z "$disk_id" ]]; then
       echo "ERROR: couldn't parse the imported disk identifier from qm importdisk's output above." >&2
       echo "The VM shell (${vmid}) and imported disk both exist -- finish attaching it by hand:" >&2
@@ -905,6 +946,12 @@ else
       exit 1
     fi
     remote "${sudo_prefix} qm set ${vmid} --scsi0 ${disk_id}"
+    # The disk data is now in ZFS; remove the source raw file (only for images
+    # we built on the node -- --image uploads are the operator's to manage).
+    if [[ -z "$image" ]]; then
+      ssh "$ssh_target" "${sudo_prefix} rm -f '${_import_path}'" 2>/dev/null || \
+        echo "Warning: couldn't remove ${_import_path} from ${node} -- you can delete it manually" >&2
+    fi
   fi
   remote "${sudo_prefix} qm set ${vmid} --boot order=scsi0"
   remote "${sudo_prefix} qm start ${vmid}"