fix(waybar): supervisor respawn + clean-restart switches; add sys-rebuild

Recovers the crashed iteration #7 (items 21+23, Latitude QA findings):

- nomarchy-waybar supervisor (waybar.nix, exec-once'd from
  hyprland.nix): any waybar exit respawns the bar; crash-loop guard
  (5 fast exits -> critical notify + stop); TERM trapped for a real
  stop. Fixes the bar-less session after a theme-switch crash.
- nomarchy-theme-sync prefers a clean `pkill -x waybar` (supervisor
  restart with fresh config+style) over the crash-prone in-place
  SIGUSR2 reload when the supervisor is running; SIGUSR2 stays as the
  unsupervised fallback.
- sys-rebuild: snapshot-first system rebuild against the CURRENT lock
  (no `nix flake update`) — the no-update twin of sys-update;
  README §3/§5 + motd list it.

Verified: V0 re-run green after crash recovery (flake check --no-build
+ py_compile); V1/V2 per the crashed session's journal entry (HM
renders exec-once=nomarchy-waybar; headless software-GL VM:
SIGKILL -> new pid, clean kill -> respawn, SIGUSR2 -> alive).
V3 pending on the Latitude (queued in HARDWARE-QUEUE.md).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/home/hyprland.nix

@@ -209,9 +209,10 @@ in
         # Waybar is launched here rather than as a systemd user service: bound
         # to graphical-session.target the unit raced Hyprland's IPC on relogin
         # and landed in `failed`; exec-once only fires once the compositor is
-        # up. Reloaded on theme switch via SIGUSR2 (nomarchy-theme-sync). See
-        # waybar.nix.
-      ] ++ lib.optional config.nomarchy.waybar.enable "waybar"
+        # up. Via the nomarchy-waybar supervisor (waybar.nix): a crash — or
+        # the clean pkill a theme switch now does — respawns the bar instead
+        # of orphaning the session bar-less.
+      ] ++ lib.optional config.nomarchy.waybar.enable "nomarchy-waybar"
         ++ lib.optional kbAutoSwitch "${keyboardWatch}/bin/nomarchy-keyboard-watch";
 
       # ── Theme-driven look ──────────────────────────────────────────

modules/home/waybar.nix

@@ -28,6 +28,37 @@ let
   # Named writeShellScriptBins (put on PATH via home.packages below) rather
   # than bare writeShellScript store paths, so the whole-swap themes' static
   # waybar.jsonc can exec them by name too — same as the swaync bell.
+  # Waybar supervisor — exec-once has no restart, so a crashed bar used to
+  # leave the session bar-less until relogin (seen on hardware: a theme
+  # switch crashed waybar mid-reload). Respawns on ANY exit — a plain
+  # `pkill -x waybar` is now a clean restart, which nomarchy-theme-sync
+  # uses instead of the crash-prone in-place SIGUSR2 reload when it sees
+  # this supervisor running. Crash-loop guard: 5 exits within 10s of
+  # their start → give up with a critical notification instead of
+  # spinning. Stop the bar for real: pkill -f nomarchy-waybar (TERM is
+  # trapped to take the child down too).
+  waybarSupervisor = pkgs.writeShellScriptBin "nomarchy-waybar" ''
+    child=
+    trap '[ -n "$child" ] && kill "$child" 2>/dev/null; exit 0' TERM INT
+    fails=0
+    while :; do
+      start=$(date +%s)
+      waybar & child=$!
+      wait "$child"; code=$?
+      if [ $(( $(date +%s) - start )) -lt 10 ]; then
+        fails=$((fails + 1))
+        if [ "$fails" -ge 5 ]; then
+          notify-send -u critical "Waybar" \
+            "Crashing on start (exit $code) — check ~/.config/waybar. Giving up." 2>/dev/null
+          exit 1
+        fi
+      else
+        fails=0
+      fi
+      sleep 1
+    done
+  '';
+
   powerProfileStatus = pkgs.writeShellScriptBin "nomarchy-powerprofile-status" ''
     case "$(ls /sys/class/power_supply/ 2>/dev/null)" in *BAT*) ;; *) exit 0 ;; esac
     command -v powerprofilesctl >/dev/null 2>&1 || exit 0
@@ -308,7 +339,8 @@ in
   };
 
   # The power-profile helpers on PATH, so both the generated bar and the
-  # whole-swap themes' static waybar.jsonc can exec them by name.
+  # whole-swap themes' static waybar.jsonc can exec them by name — plus
+  # the supervisor hyprland.nix exec-onces.
   home.packages = lib.optionals config.nomarchy.waybar.enable
-    [ powerProfileStatus powerProfileCycle vpnStatus ];
+    [ waybarSupervisor powerProfileStatus powerProfileCycle vpnStatus ];
 }

modules/nixos/default.nix

@@ -53,6 +53,7 @@ in
         ${distroName} — a NixOS desktop, themed from one JSON.
 
         sys-update                          update inputs + rebuild the system
+        sys-rebuild                         rebuild the system, no input update
         home-update                         apply home/theme changes (no sudo)
         nomarchy-theme-sync apply <theme>   switch the whole palette
         SUPER+?                             keybindings cheatsheet
@@ -312,6 +313,23 @@ in
           sudo nixos-rebuild switch --flake "$flake#default" "$@"
         fi
       '')
+      # The no-update twin (hardware-QA request): rebuild the system
+      # against the CURRENT lock — config changes only, no `nix flake
+      # update` — mirroring how home-update never touches the lock.
+      # Same snapshot-first path when available.
+      (pkgs.writeShellScriptBin "sys-rebuild" ''
+        set -e
+        if [ "$(id -u)" -eq 0 ]; then
+          echo "sys-rebuild: run as your normal user (it sudos the rebuild itself)" >&2
+          exit 1
+        fi
+        flake="''${NOMARCHY_PATH:-$HOME/.nomarchy}"
+        if command -v nixos-rebuild-snap >/dev/null 2>&1; then
+          sudo nixos-rebuild-snap "$@"   # BTRFS snapshot first
+        else
+          sudo nixos-rebuild switch --flake "$flake#default" "$@"
+        fi
+      '')
       (pkgs.writeShellScriptBin "home-update" ''
         set -e
         exec home-manager switch --flake "''${NOMARCHY_PATH:-$HOME/.nomarchy}" "$@"