Validate the cached Apple-display device path before use

The cached device path was trusted for merely existing, not for being a hiddev node, and fell back to a predictable /tmp path when XDG_RUNTIME_DIR was unset. Validate the cache shape (hiddev char device) and cache only under the user-private runtime dir; asdcontrol already gates non-Apple devices downstream, so this is defense-in-depth in the layer Omarchy owns.

bin/omarchy-brightness-display-apple

@@ -4,7 +4,13 @@
 # omarchy:args=[--no-osd] [+N%|N%-|N%]
 # omarchy:examples=omarchy brightness display apple | omarchy brightness display apple +5% | omarchy brightness display apple --no-osd 50%
 
-device_cache="${XDG_RUNTIME_DIR:-/tmp}/omarchy-brightness-display-apple.device"
+# Only cache under the user-private runtime dir. With no XDG_RUNTIME_DIR we skip
+# caching (detect every run) rather than fall back to a predictable, world-writable
+# /tmp path another user could pre-create.
+device_cache=""
+if [[ -n "${XDG_RUNTIME_DIR:-}" ]]; then
+  device_cache="$XDG_RUNTIME_DIR/omarchy-brightness-display-apple.device"
+fi
 no_osd=0
 if [[ ${1:-} == "--no-osd" ]]; then
   no_osd=1
@@ -28,9 +34,14 @@ find_apple_display_device() {
   local cached=""
   local device=""
 
-  if [[ -r $device_cache ]]; then
+  if [[ -n "$device_cache" && -r $device_cache ]]; then
     read -r cached <"$device_cache" || true
-    if [[ -n $cached && -e $cached ]]; then
+    # Trust a cached value only if it still names a hiddev character device. A
+    # stale or unexpected cache (a regular file, a non-hiddev node) is ignored and
+    # we re-detect instead of handing an arbitrary path to asdcontrol. The globs
+    # are left unquoted on purpose: [[ ]] pattern-matches an unquoted right side,
+    # and quoting them would turn the match into a literal string comparison.
+    if [[ ( $cached == /dev/hiddev* || $cached == /dev/usb/hiddev* ) && -c $cached ]]; then
       printf '%s\n' "$cached"
       return 0
     fi
@@ -39,7 +50,9 @@ find_apple_display_device() {
   device="$(detect_apple_display_device)" || return 1
   [[ -n $device ]] || return 1
 
-  printf '%s\n' "$device" >"$device_cache"
+  if [[ -n "$device_cache" ]]; then
+    printf '%s\n' "$device" >"$device_cache"
+  fi
   printf '%s\n' "$device"
 }