feat: restore portable layout on shutdown and before suspend

Add WriteConfig/Prepare backend methods (real for Hyprland, no-op for
Sway), -apply/-prepare/-no-reload CLI flags, ExecStartPre cleanup and
suspend systemd hooks so a stale docked config can never leave the
built-in display disabled after resume.

contrib/monitor-lets-go-suspend.service

@@ -0,0 +1,20 @@
+[Unit]
+Description=monitor-lets-go -- restore portable layout before suspend
+Documentation=https://github.com/mat/monitor-lets-go
+
+# Run before the system enters sleep. The ExecStop action writes a portable
+# monitor config so that on resume the compositor never loads a stale docked
+# config that would leave the built-in display disabled.
+Before=sleep.target
+
+[Service]
+# RemainAfterExit: ExecStop runs when the service is stopped (before sleep).
+# This is the standard pattern for systemd suspend hooks.
+Type=oneshot
+RemainAfterExit=yes
+
+ExecStart=/bin/true
+ExecStop=%h/.local/bin/monitor-lets-go -config %h/.config/monitor-lets-go/config.yaml -apply portable -no-reload
+
+[Install]
+WantedBy=sleep.target

contrib/monitor-lets-go-system-sleep

@@ -0,0 +1,28 @@
+#!/bin/bash
+# system-sleep hook for monitor-lets-go
+# Install to /usr/lib/systemd/system-sleep/monitor-lets-go
+#
+# Writes the portable monitor config before suspend so the compositor
+# never loads a stale docked config on resume (prevents black screen).
+#
+# Requires: sudo (passwordless for the user's own commands)
+
+case $1/$2 in
+  pre/*)
+    USER_NAME="$(logname 2>/dev/null || echo "${SUDO_USER:-$USER}")"
+    USER_UID="$(id -u "$USER_NAME" 2>/dev/null || echo 1000)"
+
+    # Extract HYPRLAND_INSTANCE_SIGNATURE from the user's systemd session
+    HYPR_ENV="$(systemctl --user -M "${USER_UID}@" show-environment 2>/dev/null)"
+    HYPR_INSTANCE="$(echo "$HYPR_ENV" | grep HYPRLAND_INSTANCE_SIGNATURE | cut -d= -f2)"
+
+    if [ -n "$HYPR_INSTANCE" ] && [ -n "$USER_NAME" ]; then
+      XDG_RUNTIME_DIR="/run/user/$USER_UID" \
+      HYPRLAND_INSTANCE_SIGNATURE="$HYPR_INSTANCE" \
+      sudo -u "$USER_NAME" \
+        /home/mat/.local/bin/monitor-lets-go \
+          -config /home/mat/.config/monitor-lets-go/config.yaml \
+          -apply portable -no-reload
+    fi
+    ;;
+esac

contrib/monitor-lets-go.service

@@ -16,6 +16,11 @@ Requires=graphical-session.target
 Type=notify
 WatchdogSec=30
 
+# Remove disabled entries from the monitor config before starting.
+# Prevents black screen if a stale docked config disables the built-in
+# display (e.g. after undocking while suspended).
+ExecStartPre=%h/.local/bin/monitor-lets-go -config %h/.config/monitor-lets-go/config.yaml -prepare
+
 ExecStart=%h/.local/bin/monitor-lets-go -config %h/.config/monitor-lets-go/config.yaml
 
 # Fast restart on failure: if the daemon crashes during docked mode,