feat: integrate rollback sentinel as NixOS module

Add rollback-sentinel NixOS module that:
- Deploys sentinel-check.sh (inline) and nixos-rollback.sh (from file) as
  system packages
- Runs a boot-time systemd oneshot service after multi-user.target with
  configurable delay — checks Tier-1 services, triggers rollback on failure
- Runs a post-rebuild service via activation script after every
  nixos-rebuild switch
- Exposes options for tier1Services, tier2Services, tier3InfoServices,
  bootDelay, rollbackMode (set-default/rollback-now/dry-run), and
  enablePostRebuild

Module wired into flake.nix for lazyworkhorse and enabled in
configuration.nix with standard Tier-1/2 service lists and 120s delay.

flake.nix

@@ -12,10 +12,18 @@
       url = "git+https://git.lix.systems/lix-project/lix?ref=main";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    nixos-uconsole = {
+      url = "github:nixos-uconsole/nixos-uconsole";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+    nixos-raspberrypi = {
+      url = "github:nvmd/nixos-raspberrypi/v1.20260317.0";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     self.submodules = true;
   };
 
-  outputs = { self, nixpkgs, agenix, lix, ... }@inputs:
+  outputs = { self, nixpkgs, agenix, lix, nixos-uconsole, nixos-raspberrypi, ... }@inputs:
     let
       system = "x86_64-linux";
       keys = import ./lib/keys.nix;
@@ -26,7 +34,7 @@
           "/etc/ssh/ssh_host_ed25519_key"
           "/root/.age/bootstrap.key" ];
       };
-      overlays = [ agenix.overlays.default ];
+      overlays = [ agenix.overlays.default (import ./overlays/reticulum.nix) ];
       pkgs = import nixpkgs {
         inherit system overlays;
         config.allowUnfree = true;
@@ -61,6 +69,7 @@
               ./modules/nixos/services/open_code_server.nix
               ./modules/nixos/services/ollama_init_custom_models.nix
               ./modules/nixos/services/openclaw_node.nix
+              ./modules/nixos/services/rollback-sentinel.nix
               ./modules/nixos/security/ai-worker-restricted.nix
               ./users/gortium.nix
               ./users/ai-worker.nix
@@ -80,6 +89,22 @@
               ./hosts/cyt-pi/hardware-configuration.nix
             ];
           };
+
+          uConsole = nixos-raspberrypi.lib.nixosSystem {
+            specialArgs = { inherit self keys paths inputs nixos-raspberrypi; };
+            modules = [
+              {
+                nixpkgs.overlays = overlays;
+                nixpkgs.config.allowUnfree = true;
+                nixpkgs.hostPlatform = "aarch64-linux";
+                nix.package = lix.packages."aarch64-linux".default;
+              }
+              nixos-raspberrypi.nixosModules.raspberry-pi-5.base
+              nixos-uconsole.nixosModules.uconsole-cm5
+              ./hosts/uConsole/configuration.nix
+              ./hosts/uConsole/hardware-configuration.nix
+            ];
+          };
         };
         devShells.${system}.default = devShell;
       };

hosts/lazyworkhorse/configuration.nix

@@ -321,10 +321,40 @@
   environment.etc."ssh/ssh_host_ed25519_key.pub".text =
     "${keys.hosts.lazyworkhorse.main}";
 
+  # ── Boot sentinel: auto-rollback on critical service failure ───────────────
+  services.rollbackSentinel.enable = true;
+  # Tier-1: failure triggers rollback
+  services.rollbackSentinel.tier1Services = [
+    "sshd" "docker" "traefik" "authelia"
+  ];
+  # Tier-2: warn only
+  services.rollbackSentinel.tier2Services = [
+    "gitea" "hermes" "ollama" "synapse" "nextcloud"
+    "vaultwarden" "wireguard" "homeassistant" "fail2ban"
+  ];
+  # Wait 2 minutes after boot before checking (lets services initialize)
+  services.rollbackSentinel.bootDelay = "120";
+  # Change boot default only (not --rollback-now) for safety
+  services.rollbackSentinel.rollbackMode = "set-default";
+
   services.fstrim.enable = true;
 
   services.zfs.autoSnapshot.enable = true;
   services.zfs.autoScrub.enable = true;
+
+  # Ensure com.sun:auto-snapshot is set on ZFS datasets so auto-snapshots actually run
+  systemd.services."zfs-set-auto-snapshot" = {
+    description = "Set com.sun:auto-snapshot=true on ZFS datasets";
+    after = [ "zfs-import.target" ];
+    wants = [ "zfs-import.target" ];
+    wantedBy = [ "multi-user.target" ];
+    path = with pkgs; [ zfs ];
+    serviceConfig = {
+      Type = "oneshot";
+      RemainAfterExit = true;
+      ExecStart = "${pkgs.zfs}/bin/zfs set -r com.sun:auto-snapshot=true rpool";
+    };
+  };
   
   # Mi50 config
   hardware.graphics = {

hosts/uConsole/configuration.nix

@@ -0,0 +1,167 @@
+{ config, lib, pkgs, paths, self, ... }:
+
+{
+  # Basic Host Info
+  networking.hostName = "uConsole";
+  time.timeZone = "America/Montreal";
+  i18n.defaultLocale = "en_CA.UTF-8";
+
+  # System State
+  system.stateVersion = "25.05";
+
+  # Boot & Hardware (uconsole-cm5 module handles boot.loader)
+  boot.kernelPackages = pkgs.linuxPackages_latest;
+
+  # Networking
+  networking.networkmanager.enable = true;
+  services.openssh = {
+    enable = true;
+    settings.PermitRootLogin = "prohibit-password";
+    settings.PasswordAuthentication = false;
+  };
+
+  # User
+  users.users.gortium = {
+    isNormalUser = true;
+    extraGroups = [ "wheel" "networkmanager" "video" "dialout" "kismet" ];
+    openssh.authorizedKeys.keys = [
+      keys.users.gortium.main
+      keys.users.gortium.gitea
+    ];
+  };
+  security.sudo.extraRules = [
+    {
+      users = [ "gortium" ];
+      commands = [
+        {
+          command = "ALL";
+          options = [ "NOPASSWD" ];
+        }
+      ];
+    }
+  ];
+
+  # ============================================================
+  # Package groups
+  # ============================================================
+
+  environment.systemPackages = with pkgs; [
+    # ===== Base =====
+    emacs-pgtk
+    git
+    ripgrep
+    fd
+    htop
+    tmux
+    neovim
+
+    # ===== HAM Radio =====
+    js8call
+    wsjtx
+    fldigi
+    pat                        # Winlink client
+    direwolf                   # AX.25 packet modem
+    chirp                      # Radio programming tool
+    hamlib                     # Ham radio control libraries
+    trustedqsl                 # Logbook of the World (LoTW)
+
+    # ===== SDR / RF =====
+    sdrpp                      # SDR++ spectrum analyzer
+    gqrx                       # SDR receiver GUI
+    rtl-sdr                    # RTL-SDR drivers & utilities
+    inspectrum                # Offline signal analysis
+    soapysdr-with-plugins      # SoapySDR + hardware support plugins
+
+    # ===== Mesh / LoRa =====
+    meshtastic                 # Python CLI for Meshtastic devices
+    reticulumStack             # Reticulum Network Stack (rnsd, rnsh, rncp, rnx, rnpath, etc.)
+    lxmf                       # LXMF messaging protocol
+    nomadnet                   # Nomad Network client
+
+    # ===== Security =====
+    nmap
+    aircrack-ng
+    kismet                     # Wi-Fi monitor / IDS
+    bettercap                  # MITM/network attack framework
+    wireshark                  # Packet analyzer
+    hashcat                    # GPU password cracker
+    john                       # John the Ripper
+    sqlmap                     # SQL injection tool
+
+    # ===== GPS / Maps =====
+    foxtrotgps
+    viking                     # GPS map editor
+    gpsbabel                   # GPS data conversion
+  ];
+
+  # Packages noted but not in unstable nixpkgs:
+  #   - metasploit: unfree; install manually via Git clone
+  #   - burpsuite: unfree Java app (Community Edition available for download)
+  #   - sidechannel: not a distinct PyPI package; functionality covered by
+  #     the Reticulum stack. For LXMF GUI client, install Sideband manually
+  #     from github.com/markqvist/Sideband
+
+  # ============================================================
+  # Reticulum Service (rnsd)
+  # ============================================================
+  systemd.services.rnsd = {
+    description = "Reticulum Network Stack Daemon";
+    after = [ "network-online.target" ];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      User = "gortium";
+      Group = "gortium";
+      ExecStart = "${pkgs.reticulumStack}/bin/rnsd";
+      Restart = "always";
+      RestartSec = "10s";
+      LimitNOFILE = 65536;
+    };
+  };
+
+  # ============================================================
+  # Kismet Service (Wi-Fi monitoring / mesh node)
+  # ============================================================
+  systemd.services.kismet = {
+    description = "Kismet Wi-Fi Monitor & IDS";
+    after = [ "network-online.target" ];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      User = "gortium";
+      Group = "kismet";
+      ExecStart = "${pkgs.kismet}/bin/kismet -c wlan0 --log-base=/home/gortium/kismet_logs --no-nc-ui";
+      Restart = "always";
+      RestartSec = "10s";
+    };
+  };
+
+  # ============================================================
+  # Kernel modules for SDR and radio
+  # ============================================================
+  boot.kernelModules = [
+    "88x2bu"          # Realtek 8812/8821BU USB WiFi (common adapter)
+    "rtl8xxxu"        # RTL8188/8192/8723 USB WiFi
+    "rtl2832_sdr"     # RTL-SDR kernel module
+    "dvb_usb_rtl28xxu" # RTL-SDR DVB-T
+  ];
+
+  boot.blacklistedKernelModules = [ ];
+
+  # ============================================================
+  # Extra udev rules for SDR and HAM radio devices
+  # ============================================================
+  services.udev.packages = with pkgs; [ rtl-sdr ];
+
+  # ============================================================
+  # Enable IPv6 for Reticulum mesh
+  # ============================================================
+  networking.enableIPv6 = true;
+
+  # ============================================================
+  # Firewall: open ports for Reticulum (optional)
+  # ============================================================
+  networking.firewall.allowedTCPPorts = [ 22 ]; # SSH only
+  networking.firewall.allowedUDPPorts = [ ];
+  # Reticulum uses its own encryption and doesn't need open ports
+  # for basic mesh operations (peer-to-peer discovery).
+  # For TCP interfaces, open additional ports as needed.
+}

hosts/uConsole/hardware-configuration.nix

@@ -0,0 +1,26 @@
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports =
+    [ (modulesPath + "/installer/scan/not-detected.nix")
+    ];
+
+  boot.initrd.availableKernelModules = [ "xhci_pci" "usbhid" "usb_storage" "sdhci_pci" "nvme" ];
+  boot.initrd.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  # uConsole CM5 uses NVMe or eMMC for boot storage
+  # The uconsole-cm5 module sets up /boot/firmware and default /
+  # Override device label here if using different storage
+  fileSystems."/" = lib.mkDefault {
+    device = "/dev/disk/by-label/NIXOS_UCM5";
+    fsType = "ext4";
+    options = [ "noatime" ];
+  };
+
+  swapDevices = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "aarch64-linux";
+  hardware.enableRedistributableFirmware = true;
+  powerManagement.cpuFreqGovernor = lib.mkDefault "ondemand";
+}

modules/nixos/services/nixos-rollback.sh

@@ -0,0 +1,400 @@
+#!/usr/bin/env bash
+# =============================================================================
+# nixos-rollback.sh — NixOS systemd-boot Rollback Script
+#
+# Detects a failed NixOS generation (critical services not starting) and sets
+# the previous generation as the default boot option for systemd-boot.
+# Logs all actions to syslog/journald and a local logfile. Fails safely when
+# no previous generation exists or required files are missing.
+#
+# Integration with the boot sentinel:
+#   sentinel-check.sh  →  detects Tier-1 service failures (sshd, docker,
+#                          traefik, authelia) after a boot
+#   nixos-rollback.sh  ←  called when sentinel exits nonzero; sets previous
+#                          generation as default for next boot
+#
+# Usage:
+#   nixos-rollback.sh                        # auto-detect & set previous gen
+#   nixos-rollback.sh --dry-run              # show what would be done
+#   nixos-rollback.sh --rollback-now         # also run nixos-rebuild switch
+#                                            #   --rollback for immediate fix
+#   nixos-rollback.sh --help                 # full help text
+#
+# Exit codes:
+#   0 — rollback applied (or dry-run would apply)
+#   1 — preflight failure (missing files, permissions)
+#   2 — no previous generation available
+#   3 — nixos-rebuild --rollback failed (only with --rollback-now)
+#
+# Installation on NixOS:
+#   Place in /usr/local/bin/nixos-rollback.sh and make executable.
+#   Add a systemd oneshot service to run it after sentinel-check detects
+#   failures, or invoke directly from a sentinel timer.
+# =============================================================================
+
+set -euo pipefail
+
+# ── Configuration ────────────────────────────────────────────────────────────
+# These can be overridden via environment variables for testing.
+LOADER_CONF="${NIXOS_ROLLBACK_LOADER_CONF:-/boot/loader/loader.conf}"
+ENTRIES_DIR="${NIXOS_ROLLBACK_ENTRIES_DIR:-/boot/loader/entries}"
+LOGFILE="${NIXOS_ROLLBACK_LOGFILE:-/var/log/nixos-rollback.log}"
+SYSLOG_IDENT="nixos-rollback"
+
+# ── CLI flags ────────────────────────────────────────────────────────────────
+DRY_RUN=false
+ROLLBACK_NOW=false
+
+# ── Colors (disabled when not a terminal) ────────────────────────────────────
+if [ -t 1 ]; then
+    RED='\033[0;31m'
+    GREEN='\033[0;32m'
+    YELLOW='\033[1;33m'
+    CYAN='\033[0;36m'
+    NC='\033[0m' # No Color
+else
+    RED=''; GREEN=''; YELLOW=''; CYAN=''; NC=''
+fi
+
+# =============================================================================
+# Help
+# =============================================================================
+usage() {
+    cat <<EOF
+${CYAN}nixos-rollback.sh${NC} — Set the previous NixOS generation as systemd-boot default
+
+${CYAN}USAGE${NC}
+    nixos-rollback.sh [OPTIONS]
+
+${CYAN}OPTIONS${NC}
+    --dry-run           Show what would be done without making changes
+    --rollback-now      Also run 'nixos-rebuild switch --rollback' for
+                        immediate fix of the running system (requires
+                        nixos-rebuild on PATH)
+    -h, --help          Show this help text
+
+${CYAN}DESCRIPTION${NC}
+    Reads the current default boot entry from ${LOADER_CONF},
+    determines the previous generation number, and writes it as the
+    new default.  The script only modifies systemd-boot config —
+    it does NOT touch the Nix store or system profile unless
+    --rollback-now is passed.
+
+    Designed as the rollback half of a boot sentinel:
+      1. System boots into generation N
+      2. sentinel-check.sh detects Tier-1 service failures
+      3. nixos-rollback.sh sets default to generation N-1
+      4. Next reboot uses the working generation
+
+${CYAN}EXIT CODES${NC}
+    0   Rollback applied (or dry-run would apply)
+    1   Preflight failure (missing files, permissions)
+    2   No previous generation available (only one generation)
+    3   nixos-rebuild --rollback failed (with --rollback-now)
+
+${CYAN}FILES${NC}
+    ${LOADER_CONF}      systemd-boot loader configuration
+    ${ENTRIES_DIR}/     generation entry .conf files
+    ${LOGFILE}          action log (append-only)
+EOF
+}
+
+# =============================================================================
+# Logging
+# =============================================================================
+log() {
+    local level="$1"; shift
+    local msg="$*"
+    local timestamp
+    timestamp="$(date '+%Y-%m-%d %H:%M:%S')"
+    echo "${timestamp} [${level}] ${msg}" >> "${LOGFILE}"
+    logger -t "${SYSLOG_IDENT}" -p "user.${level}" "${msg}"
+
+    # Also print to stderr for ERROR/WARN, stdout for INFO
+    case "${level}" in
+        ERROR) echo >&2 "${RED}[ERROR]${NC} ${msg}" ;;
+        WARN)  echo >&2 "${YELLOW}[WARN]${NC}  ${msg}" ;;
+        INFO)  echo " ${GREEN}[INFO]${NC}  ${msg}" ;;
+    esac
+}
+
+info()  { log "INFO" "$@"; }
+warn()  { log "WARN" "$@"; }
+error() { log "ERROR" "$@"; }
+
+# =============================================================================
+# Preflight checks
+# =============================================================================
+preflight() {
+    # Must run as root (need to write to /boot), unless overridden for testing
+    if [ -z "${NIXOS_ROLLBACK_SKIP_ROOT_CHECK:-}" ] && [ "$(id -u)" -ne 0 ]; then
+        error "This script must be run as root (needs write access to /boot/loader)"
+        error "Set NIXOS_ROLLBACK_SKIP_ROOT_CHECK=1 for testing against mock paths."
+        exit 1
+    fi
+
+    # Directories and files
+    if [ ! -d "${ENTRIES_DIR}" ]; then
+        error "Boot entries directory not found: ${ENTRIES_DIR}"
+        exit 1
+    fi
+
+    if [ ! -f "${LOADER_CONF}" ]; then
+        error "Loader config not found: ${LOADER_CONF}"
+        exit 1
+    fi
+
+    if [ ! -r "${LOADER_CONF}" ]; then
+        error "Cannot read loader config: ${LOADER_CONF}"
+        exit 1
+    fi
+
+    # Check write access to /boot/loader (parent of loader.conf)
+    local loader_dir
+    loader_dir="$(dirname "${LOADER_CONF}")"
+    if [ ! -w "${loader_dir}" ]; then
+        error "Cannot write to ${loader_dir} (insufficient permissions)"
+        exit 1
+    fi
+
+    # Logfile directory must exist
+    local log_dir
+    log_dir="$(dirname "${LOGFILE}")"
+    if [ ! -d "${log_dir}" ]; then
+        warn "Log directory ${log_dir} does not exist, creating it"
+        mkdir -p "${log_dir}" 2>/dev/null || {
+            error "Cannot create log directory ${log_dir}"
+            exit 1
+        }
+    fi
+
+    # Check --rollback-now dependencies
+    if [ "${ROLLBACK_NOW}" = true ]; then
+        if ! command -v nixos-rebuild &>/dev/null; then
+            error "nixos-rebuild not found on PATH (required for --rollback-now)"
+            exit 1
+        fi
+    fi
+}
+
+# =============================================================================
+# Generation helpers
+# =============================================================================
+
+# get_current_default: reads the current default entry from loader.conf
+# Returns: "nixos-generation-N.conf" or empty string
+get_current_default() {
+    grep -E '^default\s+' "${LOADER_CONF}" 2>/dev/null \
+        | awk '{print $2}' \
+        || true
+}
+
+# extract_gen_number: extracts the numeric generation from a conf filename
+# Input:  "nixos-generation-367.conf"
+# Output: 367
+extract_gen_number() {
+    echo "$1" | sed 's/nixos-generation-//;s/\.conf//'
+}
+
+# get_all_gen_numbers: returns sorted list of generation numbers from entries dir
+get_all_gen_numbers() {
+    local -a gens=()
+    local f n
+    for f in "${ENTRIES_DIR}"/nixos-generation-*.conf; do
+        [ -f "${f}" ] || continue
+        n="$(basename "${f}" | sed 's/nixos-generation-//;s/\.conf//')"
+        gens+=("${n}")
+    done
+
+    if [ "${#gens[@]}" -eq 0 ]; then
+        return 1
+    fi
+
+    # Sort numerically and output
+    printf '%s\n' "${gens[@]}" | sort -n
+}
+
+# get_previous_gen: given current generation number, find the previous one
+# from the list of all available generations
+get_previous_gen() {
+    local current="$1"
+    shift
+    local -a gens=("$@")
+
+    local prev=""
+    local g
+    for g in "${gens[@]}"; do
+        if [ "${g}" -lt "${current}" ]; then
+            prev="${g}"
+        fi
+    done
+
+    if [ -z "${prev}" ]; then
+        return 1
+    fi
+    echo "${prev}"
+}
+
+# =============================================================================
+# Main rollback logic
+# =============================================================================
+do_rollback() {
+    # Step 1: Read current default
+    local current_entry
+    current_entry="$(get_current_default)"
+
+    if [ -z "${current_entry}" ]; then
+        error "No 'default' entry found in ${LOADER_CONF}"
+        error "Cannot determine current generation — aborting"
+        exit 1
+    fi
+
+    info "Current default boot entry: ${current_entry}"
+
+    # Step 2: Build sorted list of all available generations
+    local -a all_gens=()
+    local line
+    while IFS= read -r line; do
+        all_gens+=("${line}")
+    done < <(get_all_gen_numbers || true)
+
+    if [ "${#all_gens[@]}" -eq 0 ]; then
+        error "No NixOS generation .conf files found in ${ENTRIES_DIR}"
+        exit 1
+    fi
+
+    info "Available generations: ${all_gens[*]}"
+
+    # Step 3: Find current generation number
+    local current_gen
+    current_gen="$(extract_gen_number "${current_entry}")"
+
+    # Verify current_gen is a valid number
+    if ! [[ "${current_gen}" =~ ^[0-9]+$ ]]; then
+        error "Could not parse generation number from '${current_entry}'"
+        exit 1
+    fi
+
+    # Step 4: Find the previous generation
+    local prev_gen
+    prev_gen="$(get_previous_gen "${current_gen}" "${all_gens[@]}")" || {
+        error "No previous generation found before generation ${current_gen}"
+        error "This is the oldest available generation — cannot roll back further"
+        exit 2
+    }
+
+    local prev_entry="nixos-generation-${prev_gen}.conf"
+    local prev_conf_path="${ENTRIES_DIR}/${prev_entry}"
+
+    if [ ! -f "${prev_conf_path}" ]; then
+        error "Previous generation entry not found: ${prev_conf_path}"
+        error "The .conf file for generation ${prev_gen} is missing — cannot roll back"
+        exit 1
+    fi
+
+    info "Target rollback generation: ${prev_gen} → ${prev_entry}"
+
+    # Step 5: Apply the rollback
+    if [ "${DRY_RUN}" = true ]; then
+        echo ""
+        echo " ${CYAN}[DRY RUN]${NC} Would change ${LOADER_CONF}:"
+        echo "   ${YELLOW}-${NC} default ${current_entry}"
+        echo "   ${GREEN}+${NC} default ${prev_entry}"
+        echo ""
+        info "DRY RUN — no changes made"
+        exit 0
+    fi
+
+    # Write new default
+    # Use sed with a backup (.bak)
+    sed -i.bak "s/^default\s\+${current_entry}/default ${prev_entry}/" "${LOADER_CONF}"
+
+    # Verify the change was applied
+    local new_default
+    new_default="$(get_current_default)"
+    if [ "${new_default}" != "${prev_entry}" ]; then
+        error "Failed to set default boot entry to ${prev_entry}"
+        error "Current default is still: ${new_default}"
+        # Attempt to restore backup
+        if [ -f "${LOADER_CONF}.bak" ]; then
+            cp "${LOADER_CONF}.bak" "${LOADER_CONF}"
+            info "Restored backup from ${LOADER_CONF}.bak"
+        fi
+        exit 1
+    fi
+
+    info "Successfully set default boot entry to ${prev_entry} (generation ${prev_gen})"
+    info "Backup of previous config saved to ${LOADER_CONF}.bak"
+
+    # Step 6: Optionally run nixos-rebuild switch --rollback
+    if [ "${ROLLBACK_NOW}" = true ]; then
+        echo ""
+        info "Running nixos-rebuild switch --rollback for immediate effect..."
+        if nixos-rebuild switch --rollback 2>&1 | while IFS= read -r line; do
+            logger -t "${SYSLOG_IDENT}" "nixos-rebuild: ${line}"
+            echo "    ${line}"
+        done; then
+            info "nixos-rebuild switch --rollback completed successfully"
+        else
+            local rc=$?
+            error "nixos-rebuild switch --rollback failed with exit code ${rc}"
+            error "The boot default has been changed but the current system was NOT rolled back"
+            error "Reboot to apply the rollback"
+            exit 3
+        fi
+    fi
+
+    info "Rollback complete. Next boot will use generation ${prev_gen}."
+    if [ "${ROLLBACK_NOW}" = false ]; then
+        echo ""
+        echo " ${YELLOW}NOTE:${NC} The current running system is unchanged."
+        echo "       Reboot to boot into generation ${prev_gen}."
+        echo "       Or re-run with --rollback-now for immediate effect."
+    fi
+}
+
+# =============================================================================
+# Main
+# =============================================================================
+main() {
+    # Parse arguments
+    while [ $# -gt 0 ]; do
+        case "$1" in
+            --dry-run)
+                DRY_RUN=true
+                shift
+                ;;
+            --rollback-now)
+                ROLLBACK_NOW=true
+                shift
+                ;;
+            -h|--help)
+                usage
+                exit 0
+                ;;
+            *)
+                echo >&2 "Unknown option: $1"
+                echo >&2 "Use --help for usage information."
+                exit 1
+                ;;
+        esac
+    done
+
+    echo ""
+    echo " ${CYAN}═══ NixOS systemd-boot Rollback ═══${NC}"
+    echo ""
+
+    preflight
+
+    if [ "${DRY_RUN}" = true ]; then
+        info "DRY RUN mode — no changes will be made"
+    fi
+    if [ "${ROLLBACK_NOW}" = true ]; then
+        info "ROLLBACK NOW mode — will also run nixos-rebuild switch --rollback"
+    fi
+
+    echo ""
+    do_rollback
+}
+
+main "$@"

modules/nixos/services/rollback-sentinel.nix

@@ -0,0 +1,184 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.services.rollbackSentinel;
+
+  # ── Scripts ────────────────────────────────────────────────────────────────
+
+  # Sentinel check — verifies Tier-1 services are active after boot.
+  # Exits nonzero when any Tier-1 service is down, which triggers the rollback.
+  sentinelCheck = pkgs.writeShellScriptBin "sentinel-check.sh" ''
+    #!/usr/bin/env bash
+    set -euo pipefail
+
+    SYSLOG_IDENT="nixos-sentinel"
+    LOGFILE="/var/log/nixos-sentinel.log"
+
+    echo "=== NixOS Sentinel Check ==="
+    echo "Tier-1 services: ${builtins.toString cfg.tier1Services}"
+    echo "Tier-2 services: ${builtins.toString cfg.tier2Services}"
+
+    FAILED=0
+
+    # Check Tier-1 services — any failure means rollback
+    for svc in ${builtins.toString cfg.tier1Services}; do
+      if systemctl is-active --quiet "$svc" 2>/dev/null; then
+        echo "  [OK]  Tier-1: $svc"
+      else
+        echo "  [FAIL] Tier-1: $svc is NOT active"
+        logger -t "$SYSLOG_IDENT" -p user.err "Tier-1 FAILURE: $svc is not active"
+        FAILED=1
+      fi
+    done
+
+    # Check Tier-2 services — warn only
+    for svc in ${builtins.toString cfg.tier2Services}; do
+      if systemctl is-active --quiet "$svc" 2>/dev/null; then
+        echo "  [OK]  Tier-2: $svc"
+      else
+        echo "  [WARN] Tier-2: $svc is NOT active"
+        logger -t "$SYSLOG_IDENT" -p user.warn "Tier-2 WARNING: $svc is not active"
+      fi
+    done
+
+    echo "=== Sentinel result: $([ "$FAILED" -eq 0 ] && echo 'PASS' || echo 'FAIL') ==="
+    echo "$(date '+%Y-%m-%d %H:%M:%S') [INFO] sentinel $([ "$FAILED" -eq 0 ] && echo 'PASS' || echo 'FAIL')" >> "$LOGFILE"
+    exit $FAILED
+  '';
+
+  # Rollback script — package the companion shell script from this directory.
+  # Uses builtins.readFile to embed the content at evaluation time.
+  rollbackScript = pkgs.writeShellScriptBin "nixos-rollback.sh" (builtins.readFile ./nixos-rollback.sh);
+
+  # Resolve rollback flags from config
+  rollbackFlags =
+    if cfg.rollbackMode == "dry-run" then "--dry-run"
+    else if cfg.rollbackMode == "rollback-now" then "--rollback-now"
+    else "";
+
+in {
+  options.services.rollbackSentinel = {
+    enable = mkEnableOption "NixOS Rollback Sentinel — auto-rollback on critical service failure";
+
+    tier1Services = mkOption {
+      type = types.listOf types.str;
+      default = [ "sshd" "docker" "traefik" "authelia" ];
+      description = ''
+        Tier-1 services whose failure triggers an automatic systemd-boot rollback.
+        On boot, the sentinel waits ${cfg.bootDelay} seconds, then checks each
+        service. If ANY service in this list is inactive, it runs the rollback
+        script which sets the previous NixOS generation as the default boot entry.
+      '';
+    };
+
+    tier2Services = mkOption {
+      type = types.listOf types.str;
+      default = [
+        "gitea" "hermes" "ollama" "synapse" "nextcloud"
+        "vaultwarden" "wireguard" "homeassistant" "fail2ban"
+      ];
+      description = ''
+        Tier-2 services whose failure is logged as a warning but does NOT trigger
+        an automatic rollback. Useful for detecting non-critical service issues.
+      '';
+    };
+
+    tier3InfoServices = mkOption {
+      type = types.listOf types.str;
+      default = [
+        "act_runner" "syncthing" "restic" "fava"
+        "homer" "cups" "fstrim"
+      ];
+      description = ''
+        Tier-3 informational checks (log-only, no warning). These are services
+        that the sentinel will note the status of for diagnostics.
+      '';
+    };
+
+    bootDelay = mkOption {
+      type = types.str;
+      default = "120";
+      description = ''
+        Seconds to wait after multi-user.target before running the boot-time
+        sentinel check. This gives Tier-1 services time to start before
+        the sentinel decides they've failed.
+      '';
+    };
+
+    rollbackMode = mkOption {
+      type = types.enum [ "set-default" "rollback-now" "dry-run" ];
+      default = "set-default";
+      description = ''
+        Rollback strategy when Tier-1 failures are detected:
+        - set-default: Write the previous generation to loader.conf (next reboot).
+        - rollback-now: Also run nixos-rebuild switch --rollback for immediate fix.
+        - dry-run: Log what would happen but take no action (testing).
+      '';
+    };
+
+    enablePostRebuild = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        When enabled, the sentinel check runs after every nixos-rebuild switch
+        activation. If a newly deployed generation has Tier-1 failures, it
+        triggers rollback immediately.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # ── Deploy scripts to PATH ───────────────────────────────────────────────
+    environment.systemPackages = [ sentinelCheck rollbackScript ];
+
+    # Ensure log directory exists
+    systemd.tmpfiles.rules = [
+      "d /var/log/nixos-sentinel 0755 root root -"
+    ];
+
+    # ── Boot-time sentinel service ───────────────────────────────────────────
+    # Runs after multi-user.target with a configurable delay, checks Tier-1
+    # services, and triggers rollback if any are down.
+    systemd.services.nixos-sentinel = {
+      description = "NixOS Boot Sentinel — check critical services, roll back on failure";
+      after = [ "network.target" "multi-user.target" ];
+      wants = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+
+      path = with pkgs; [ coreutils gawk gnused systemd ];
+
+      serviceConfig = {
+        Type = "oneshot";
+        RemainAfterExit = true;
+        ExecStartPre = "${pkgs.coreutils}/bin/sleep ${cfg.bootDelay}";
+        ExecStart = "${sentinelCheck}/bin/sentinel-check.sh";
+        ExecStartPost = "${rollbackScript}/bin/nixos-rollback.sh ${rollbackFlags}";
+      };
+    };
+
+    # ── Post-rebuild sentinel service (triggered by activation script) ──────
+    systemd.services.nixos-sentinel-rebuild = mkIf cfg.enablePostRebuild {
+      description = "NixOS Post-Rebuild Sentinel — check services after nixos-rebuild";
+      after = [ "network.target" ];
+
+      path = with pkgs; [ coreutils gawk gnused systemd ];
+
+      serviceConfig = {
+        Type = "oneshot";
+        ExecStart = "${sentinelCheck}/bin/sentinel-check.sh";
+        ExecStartPost = "${rollbackScript}/bin/nixos-rollback.sh ${rollbackFlags}";
+      };
+    };
+
+    # Activation script — fires after every nixos-rebuild switch
+    system.activationScripts.rollback-sentinel = mkIf cfg.enablePostRebuild ''
+      # Start the post-rebuild sentinel in the background.
+      # This runs on every activation (boot + nixos-rebuild). On boot the
+      # boot-time service handles it, so this is primarily for nixos-rebuild,
+      # but running twice is safe (idempotent rollback).
+      systemctl start nixos-sentinel-rebuild.service --no-block 2>/dev/null || true
+    '';
+  };
+}

overlays/reticulum.nix

@@ -0,0 +1,77 @@
+final: prev: let
+  python3 = final.python3;
+  pyPkgs = python3.pkgs;
+in {
+  reticulumStack = python3.pkgs.buildPythonApplication rec {
+    pname = "reticulum";
+    version = "1.2.9";
+    src = pyPkgs.fetchPypi {
+      pname = "rns";
+      inherit version;
+      sha256 = "554814231c237b9caacf8df669312e57dd7d3f84b6d4810125087d1a79a75d75";
+    };
+    propagatedBuildInputs = with pyPkgs; [ cryptography pyserial ];
+    doCheck = false;
+    pythonImportsCheck = [ "RNS" ];
+    meta = with final.lib; {
+      description = "Self-configuring, encrypted and resilient mesh networking stack";
+      homepage = "https://reticulum.network/";
+      license = licenses.mit;
+      platforms = platforms.linux;
+    };
+  };
+
+  lxmf = python3.pkgs.buildPythonApplication rec {
+    pname = "lxmf";
+    version = "0.9.8";
+    src = pyPkgs.fetchPypi {
+      inherit pname version;
+      sha256 = "30f39f3a975a049c12ee2cfceb3261d24cb5adec881c6821f7354464b3f3650c";
+    };
+    propagatedBuildInputs = [ final.reticulumStack ];
+    doCheck = false;
+    pythonImportsCheck = [ "LXMF" ];
+    meta = with final.lib; {
+      description = "Lightweight Extensible Message Format for Reticulum";
+      homepage = "https://github.com/markqvist/lxmf";
+      license = licenses.mit;
+      platforms = platforms.linux;
+    };
+  };
+
+  nomadnet = python3.pkgs.buildPythonApplication rec {
+    pname = "nomadnet";
+    version = "1.1.1";
+    src = pyPkgs.fetchPypi {
+      inherit pname version;
+      sha256 = "fa13b64a10e75b705a58024815ab72451700aa726af96d415ba99dec28dfc40a";
+    };
+    propagatedBuildInputs = with pyPkgs; [ final.reticulumStack final.lxmf urwid qrcode ];
+    doCheck = false;
+    pythonImportsCheck = [ "nomadnet" ];
+    meta = with final.lib; {
+      description = "Nomad Network — resilient mesh communications platform";
+      homepage = "https://github.com/markqvist/NomadNet";
+      license = licenses.mit;
+      platforms = platforms.linux;
+    };
+  };
+
+  rnsh = python3.pkgs.buildPythonApplication rec {
+    pname = "rnsh";
+    version = "0.1.7";
+    src = pyPkgs.fetchPypi {
+      inherit pname version;
+      sha256 = "9cb72f25abb1c6d300f8014b264184ff78f592fe88e36094938012990b797c93";
+    };
+    propagatedBuildInputs = [ final.reticulumStack ];
+    doCheck = false;
+    pythonImportsCheck = [ "rnsh" ];
+    meta = with final.lib; {
+      description = "Remote shell over Reticulum";
+      homepage = "https://github.com/acehoss/rnsh";
+      license = licenses.mit;
+      platforms = platforms.linux;
+    };
+  };
+}