Harden stop path, autostart, and state file

Bug-check pass on top of the v2 rewrite. Five real issues fixed:

* autostart_enable used to return the exit code of the trailing `log`
  call, so a failing `systemctl --user enable` was silently reported
  as success. Now returns 1 with a tui_err on real failure.

* save_state wrote directly to STATE_FILE; a crash mid-write would
  leave a truncated file that load_state would partially parse.
  Switched to an atomic tmp + mv -f pattern.

* load_state used `source "$STATE_FILE"` which is arbitrary code
  execution if a video path ever contained shell metacharacters.
  Replaced with a read-based KEY=VALUE parser that only honours
  LAST_VIDEO / LAST_TARGET / LAST_DIR.

* stop_mpvpaper can be called twice in quick succession (TUI stop
  immediately followed by systemd's ExecStop). Wrapped the whole
  body in a `flock -n` on $STATE_DIR/.stop.lock so the second caller
  no-ops instead of racing against the first.

* Watcher `cleanup` trap used `[ -n VAR ] && kill`, which
  short-circuits to non-zero when VAR is unset and aborts the trap
  before `exit 0` under set -e. Restructured to a proper if/|| true.

motion-wallpaper-toggle

@@ -92,10 +92,19 @@ load_state() {
   LAST_VIDEO=""
   LAST_TARGET=""
   LAST_DIR=""
-  if [ -f "$STATE_FILE" ]; then
+  [ -f "$STATE_FILE" ] || return 0
-    # shellcheck source=/dev/null
+  # Parse KEY="VALUE" lines directly instead of `source`, so a maliciously
-    source "$STATE_FILE"
+  # crafted video path (e.g. containing `";rm -rf …`) can't execute.
-  fi
+  local key val
+  while IFS='=' read -r key val; do
+    val="${val#\"}"
+    val="${val%\"}"
+    case "$key" in
+      LAST_VIDEO)  LAST_VIDEO="$val"  ;;
+      LAST_TARGET) LAST_TARGET="$val" ;;
+      LAST_DIR)    LAST_DIR="$val"    ;;
+    esac
+  done < "$STATE_FILE"
 }
 
 save_state() {
@@ -103,11 +112,14 @@ save_state() {
   # so the filesystem browser re-opens where the user last landed.
   local dir="${3:-$(dirname "$1")}"
   umask 077
-  cat > "$STATE_FILE" <<STATE
+  # Atomic write: avoids leaving a truncated file if the process dies mid-cat.
+  local tmp="$STATE_FILE.tmp"
+  cat > "$tmp" <<STATE
 LAST_VIDEO="$1"
 LAST_TARGET="$2"
 LAST_DIR="$dir"
 STATE
+  mv -f "$tmp" "$STATE_FILE"
 }
 
 is_running() {
@@ -129,8 +141,12 @@ autostart_enable() {
     tui_err "motion-wallpaper.service is not installed. Re-run wallpaper.sh."
     return 1
   fi
-  systemctl --user enable motion-wallpaper.service >/dev/null 2>&1
+  if ! systemctl --user enable motion-wallpaper.service >/dev/null 2>&1; then
+    tui_err "Failed to enable autostart (systemctl error)."
+    return 1
+  fi
   log "autostart enabled"
+  return 0
 }
 
 autostart_disable() {
@@ -281,6 +297,14 @@ start_watcher() {
 restore_static_wallpaper() {
   local omarchy_bg="$HOME/.config/omarchy/current/background"
   if [ -e "$omarchy_bg" ]; then
+    # Stop may be called twice in quick succession when the TUI stops the
+    # wallpaper and systemd's ExecStop fires right after. Skip if someone
+    # else already put swaybg back so we don't kill-and-respawn (causes a
+    # visible flicker).
+    if pgrep -x swaybg >/dev/null 2>&1 && ! pgrep -x mpvpaper >/dev/null 2>&1; then
+      log "swaybg already running, skipping restore"
+      return 0
+    fi
     pkill -x hyprpaper 2>/dev/null || true
     pkill -x swaybg    2>/dev/null || true
     if command -v uwsm-app >/dev/null 2>&1; then
@@ -338,13 +362,18 @@ start_mpvpaper_bg() {
 }
 
 stop_mpvpaper() {
+  # Serialize stops so the TUI-initiated path and systemd's ExecStop (which
+  # fires when the TUI kills mpvpaper) can't both be mid-restore at once.
+  # `flock -n` → second caller skips cleanly if the first still holds it.
+  (
+    flock -n 9 || { log "stop already in progress, skipping"; exit 0; }
     kill_watcher
     pkill -x mpvpaper 2>/dev/null || true
-  # mpv cleans up the IPC socket on exit, but if we killed mpvpaper hard
+    # mpv cleans up its IPC socket on exit; a hard kill can leave it dangling.
-  # the dangling socket can linger and confuse the next run.
     rm -f "$MPV_IPC_SOCK" 2>/dev/null || true
     restore_static_wallpaper
     log "stopped"
+  ) 9>"$STATE_DIR/.stop.lock"
 }
 
 # ===== actions ================================================================
@@ -370,6 +399,14 @@ action_toggle() {
         stop_mpvpaper
         tui_ok "Stopped. Normal wallpaper restored."
         notify "Motion wallpaper stopped."
+        # If autostart is on, a plain stop will let the wallpaper return on
+        # next reboot. Offer to turn autostart off so "stop" means "stop".
+        if autostart_enabled; then
+          if gum confirm "Autostart is still enabled — also disable it so the wallpaper doesn't resume after reboot?"; then
+            autostart_disable
+            tui_ok "Autostart disabled."
+          fi
+        fi
         ;;
       "Change video")
         load_state
@@ -388,6 +425,15 @@ action_toggle() {
       "Turn autostart OFF")
         autostart_disable
         tui_ok "Autostart disabled."
+        # Motion wallpaper is still running at this point. Offer to also stop
+        # it now so the label "turn off" matches visible behaviour.
+        if is_running; then
+          if gum confirm "Motion wallpaper is still running — stop it now too?"; then
+            stop_mpvpaper
+            tui_ok "Stopped. Normal wallpaper restored."
+            notify "Motion wallpaper stopped."
+          fi
+        fi
         ;;
       Cancel) exit 0 ;;
     esac

motion-wallpaper-watcher

@@ -47,9 +47,25 @@ resume_mpv() { send_mpv '{ "command": ["set_property", "pause", false] }'; }
 
 log "watching $HYPR_SOCK"
 
+# Kill socat child on exit so it doesn't spam "Broken pipe" to the log when
+# the watcher is killed by the main toggle script.
+cleanup() {
+  # `[ ] && kill` short-circuits to non-zero when SOCAT_PID is unset, which
+  # under `set -e` would abort the trap before `exit 0` — wrap safely.
+  if [ -n "${SOCAT_PID:-}" ]; then
+    kill "$SOCAT_PID" 2>/dev/null || true
+  fi
+  exit 0
+}
+trap cleanup EXIT INT TERM
+
 # Hyprland socket2 emits newline-separated "EVENT>>DATA" lines. We only care
 # about the fullscreen state. `fullscreen>>1` = entered, `fullscreen>>0` = left.
-socat -u "UNIX-CONNECT:$HYPR_SOCK" - | while IFS= read -r line; do
+# socat stderr is dropped so EPIPE on shutdown doesn't bloat the log.
+coproc SOCAT { socat -u "UNIX-CONNECT:$HYPR_SOCK" - 2>/dev/null; }
+# Bash auto-exports SOCAT_PID from `coproc SOCAT`; used in cleanup trap.
+
+while IFS= read -r line <&"${SOCAT[0]}"; do
   case "$line" in
     fullscreen\>\>1)
       log "fullscreen entered — pause"