feat(menu): one fingerprint switch, an auto-login toggle, and the state bridge they needed

Bernardo, post-reboot: "Use for login" was the wrong question. Whether the
finger works is one decision, not two, and whether login prompts at all is
a different decision that was never in the menu.

System › Fingerprint is now a single Fingerprint (on/off) switch, leading
the menu with enroll/list/verify/delete as the plumbing behind it. It
writes the one settings.fingerprint.pam key, and modules/home/idle.nix now
defaults idle.fingerprint from that same key — so the lock screen and
login/sudo move together instead of drifting apart the way they did until
e2de906. nomarchy-fingerprint does the two rebuilds this needs (sudo
system for PAM, home switch for hyprlock) and refuses to turn on with no
finger enrolled.

System › Auto-login is new (nomarchy-autologin), and it is what decides
whether anything is asked at boot: auto-login on means no prompt whatever
the fingerprint switch says; off means the greeter asks, for a password or
a finger. Installer-seeded ON for LUKS machines — the passphrase already
gates the disk — and off without it, where the greeter is the only thing
between power-on and the desktop.

Both had to become state-owned to be toggleable at all, which surfaced two
real bugs:

  * nomarchy.system.greeter.autoLogin defaulted from
    `config.nomarchy.settings…` — an attribute that exists ONLY on the Home
    Manager side. On NixOS it is absent and `or null` swallowed the error,
    so the default silently evaluated to null on every machine ever built.
    That is why the installer baked a Nix line: the state path never
    worked. Now read via theme-state-read.nix (the hardware.nix/timezone.nix
    pattern) and mkDefault'd, so the menu owns it and a hand-set line still
    pins it. Two more options read the same phantom bridge — BACKLOG #116.
  * `theme-sync get` printed Python's "None" for a JSON null, so every
    `case … null)` a caller writes would miss. Now prints "null", as the
    comment above it already promised for booleans.

The installer seeds the state instead of emitting the system.nix line,
because that line outranks the state and would strand the toggle.

V1 (V3 pending: HARDWARE-QUEUE). nix flake check --no-build, installer-
safety and option-docs all pass. Proved by eval/build, not assumed: a state
carrying autoLogin yields greetd initial_session {"user":"bernardo"}, the
template state (no autoLogin) yields none, and a hand-set null beats a state
that says otherwise; a state with only fingerprint.pam=true — nothing set by
hand — renders the hyprlock auth.fingerprint block; both new tools pass
bash -n and land in systemPackages (nomarchy-fingerprint only with a
reader); the patcher writes settings.greeter.autoLogin and no system.nix
line; and the get round trip prints null, so the menu reads "Auto-login
(off)" where it would have read "(on)".

The reader itself, the two rebuilds, and the reboot are hardware — queued.

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

modules/nixos/greeter.nix

@@ -14,16 +14,67 @@
 #      theme's colors). ANSI "black" stays dark even in light themes —
 #      the greeter reads terminal-dark there, the same convention every
 #      terminal applies to ANSI colors.
+#
+# Auto-login is in-flake state like the rest (settings.greeter.autoLogin,
+# written by System › Auto-login via nomarchy-autologin below), NOT a baked
+# line in system.nix: a hand-set `nomarchy.system.greeter.autoLogin` outranks
+# the state default, which would leave the menu toggle flipping JSON that
+# nothing reads. The installer therefore seeds the STATE on LUKS machines and
+# the template keeps its example commented (templates/downstream/system.nix).
 { config, lib, pkgs, ... }:
 
 let
   cfg = config.nomarchy.system;
   distroName = config.system.nixos.distroName;
 
+  sync = lib.getExe pkgs.nomarchy-theme-sync;
+
+  # Menu/CLI toggle, same shape as nomarchy-autotimezone: runs as the normal
+  # user (it owns the flake checkout + writes the state), sudos only the
+  # system switch. greetd's initial_session is baked at system rebuild, so
+  # there is nothing to apply live — the next boot is the observable change.
+  nomarchy-autologin = pkgs.writeShellScriptBin "nomarchy-autologin" ''
+    set -e
+    if [ "$(id -u)" -eq 0 ]; then
+      echo "nomarchy-autologin: run as your normal user (it sudos the rebuild itself)" >&2
+      exit 1
+    fi
+    flake="''${NOMARCHY_PATH:-$HOME/.nomarchy}"
+
+    cur=$(${sync} get settings.greeter.autoLogin 2>/dev/null) || cur=null
+    case "''${1:-toggle}" in
+      on)     new="\"$USER\"" ;;
+      off)    new=null ;;
+      toggle) case "$cur" in null|""|None) new="\"$USER\"" ;; *) new=null ;; esac ;;
+      status) echo "$cur"; exit 0 ;;
+      *) echo "usage: nomarchy-autologin [toggle|on|off|status]" >&2; exit 64 ;;
+    esac
+
+    ${sync} --quiet set settings.greeter.autoLogin "$new" --no-switch
+
+    notify-send "Auto-login" "Rebuilding the system…" 2>/dev/null || true
+    sudo nixos-rebuild switch --flake "$flake#default"
+
+    if [ "$new" = null ]; then
+      notify-send "Auto-login off" "The greeter asks who you are on the next boot." 2>/dev/null || true
+    else
+      notify-send "Auto-login on" "Next boot goes straight to the desktop." 2>/dev/null || true
+    fi
+  '';
+
   state =
     if cfg.stateFile != null
     then builtins.fromJSON (builtins.readFile cfg.stateFile)
     else { };
+
+  # The auto-login user from the state, or null. Read here via the state file
+  # — NOT `config.nomarchy.settings`, which exists only on the Home Manager
+  # side: on NixOS that attribute is missing, and `or null` swallows the
+  # error, so the old default silently evaluated to null on every machine.
+  stateAutoLogin =
+    let v = (state.settings or { }).greeter.autoLogin or null;
+    in if builtins.isString v && v != "" then v else null;
+
   # A sparse/hand-rolled state without a proper ansi block just skips the
   # theming (stock tuigreet grey) — never an eval error.
   ansi = state.ansi or [ ];
@@ -44,6 +95,15 @@ let
 in
 {
   config = {
+    # Shipped unconditionally so the menu can turn auto-login back ON while
+    # it's off — the same reason nomarchy-autotimezone is unconditional.
+    environment.systemPackages = [ nomarchy-autologin ];
+
+    # Track the in-flake flag; mkDefault so a hand-set
+    # nomarchy.system.greeter.autoLogin in system.nix still wins (the
+    # autoTimezone pattern).
+    nomarchy.system.greeter.autoLogin = lib.mkDefault stateAutoLogin;
+
     # VT palette from the theme (RRGGBB, no #; lands as vt.default_* kernel
     # params). mkDefault so a downstream console.colors wins.
     console.colors = lib.mkIf themed (lib.mkDefault (map (lib.removePrefix "#") ansi));

modules/nixos/hardware.nix

@@ -23,6 +23,58 @@ let
     then import ../theme-state-read.nix { inherit lib; } config.nomarchy.system.stateFile
     else { };
   pamFromState = (hwState.settings or { }).fingerprint.pam or false;
+
+  sync = lib.getExe pkgs.nomarchy-theme-sync;
+
+  # The single fingerprint on/off switch (System › Fingerprint). One state key
+  # for one user-facing decision — it drives login/sudo PAM here AND the
+  # hyprlock unlock in modules/home/idle.nix, which reads the same
+  # settings.fingerprint.pam. Two rebuilds, because the two live in different
+  # configurations: sudo the system switch (PAM), then a home switch
+  # (hyprlock). Same user-owns-the-flake shape as nomarchy-autotimezone.
+  #
+  # This does NOT decide whether login prompts at all — auto-login skips the
+  # greeter entirely, so "fingerprint on" adds the finger to whatever prompts
+  # actually happen (sudo, lock screen, and the greeter only when auto-login
+  # is off). See nomarchy-autologin in ./greeter.nix.
+  nomarchy-fingerprint = pkgs.writeShellScriptBin "nomarchy-fingerprint" ''
+    set -e
+    if [ "$(id -u)" -eq 0 ]; then
+      echo "nomarchy-fingerprint: run as your normal user (it sudos the rebuild itself)" >&2
+      exit 1
+    fi
+    flake="''${NOMARCHY_PATH:-$HOME/.nomarchy}"
+
+    cur=$(${sync} get settings.fingerprint.pam 2>/dev/null) || cur=false
+    case "''${1:-toggle}" in
+      on)     new=true ;;
+      off)    new=false ;;
+      toggle) case "$cur" in true|True) new=false ;; *) new=true ;; esac ;;
+      status) echo "$cur"; exit 0 ;;
+      *) echo "usage: nomarchy-fingerprint [toggle|on|off|status]" >&2; exit 64 ;;
+    esac
+
+    # Turning it ON with no enrolled finger would advertise a scan that cannot
+    # succeed on every prompt — refuse instead, and say where to go.
+    if [ "$new" = true ] \
+      && fprintd-list "$USER" 2>/dev/null | grep -qiE 'no fingers enrolled|No devices available'; then
+      notify-send "Fingerprint" "Enroll a finger first (System › Fingerprint › Enroll)." 2>/dev/null || true
+      echo "nomarchy-fingerprint: no finger enrolled — run fprintd-enroll first" >&2
+      exit 1
+    fi
+
+    ${sync} --quiet set settings.fingerprint.pam "$new" --no-switch
+
+    notify-send "Fingerprint" "Rebuilding…" 2>/dev/null || true
+    sudo nixos-rebuild switch --flake "$flake#default"
+    home-manager switch --flake "$flake"
+
+    if [ "$new" = true ]; then
+      notify-send "Fingerprint on" "Password or finger — at sudo, the lock screen, and the greeter." 2>/dev/null || true
+    else
+      notify-send "Fingerprint off" "Password only. Enrolled fingers are kept." 2>/dev/null || true
+    fi
+  '';
 in
 {
   options.nomarchy.hardware = {
@@ -214,6 +266,9 @@ in
     # every interactive service we care about to follow our opt-in flag.
     (lib.mkIf cfg.fingerprint.enable {
       services.fprintd.enable = true;
+      # Ships whenever a reader exists, regardless of the pam flag: the
+      # toggle's whole job is to turn the flag back on while it's off.
+      environment.systemPackages = [ nomarchy-fingerprint ];
       security.pam.services = lib.genAttrs [
         "login" "sudo" "su" "greetd" "hyprlock" "sshd"
         "passwd" "chsh" "chfn" "chpasswd"

modules/nixos/options.nix

@@ -11,13 +11,20 @@
 
     greeter.autoLogin = lib.mkOption {
       type = lib.types.nullOr lib.types.str;
-      default = config.nomarchy.settings.greeter.autoLogin or null;
+      default = null;
+      defaultText = lib.literalExpression
+        "(settings.greeter.autoLogin from theme-state.json) or null";
       example = "ada";
       description = ''
         Log this user straight into Hyprland on boot (greetd
         initial_session); logging out lands on the normal greeter.
-        The installer sets it on LUKS-encrypted machines — the disk
-        passphrase already gates access, a second prompt is ceremony.
+
+        Normally you leave this alone and use System › Auto-login, which
+        writes `settings.greeter.autoLogin` in theme-state.json —
+        ./greeter.nix mkDefaults this option from it. The installer seeds
+        that state on LUKS-encrypted machines: the disk passphrase already
+        gates access, so a second prompt is ceremony. Setting this option by
+        hand pins the choice and the menu toggle can no longer move it.
       '';
     };