chksysconfig: merge missing settings instead of overwriting user config

The verify function checks for a missing system.hostname to detect a
corrupt or truncated system.cfg. The intent is to restore defaults so
the system boots correctly. However, the current implementation runs
`rsync -a /usr/config/ /storage/.config` which overwrites the entire
user config tree — WiFi credentials, SSH settings, emulator preferences
and per-game overrides are all replaced with factory defaults.

This creates a cycle: the full rsync restores system.hostname, but
EmulationStation's save logic strips settings that match its internal
defaults (including system.hostname). On the next hard crash, the
hostname is missing again, triggering another full overwrite.

Replace the destructive rsync with a merge that adds keys present in
the reference config but missing from the user config. Existing user
settings are preserved. Retroarch config restoration is separated to
only run when those specific files are actually missing.

Observed on RK3566 (RGB30) during thermal shutdown and on Retroid
Pocket 5 during hard crashes from stress testing.

Author: aenertia

projects/ROCKNIX/packages/rocknix/sources/scripts/chksysconfig

@@ -18,17 +18,38 @@ restore() {
   cp ${CFG_PATH}/system.cfg.backup ${CFG_PATH}/system.cfg
 }
 
+merge_missing_settings() {
+  local ref="/usr/config/system/configs/system.cfg"
+  [ ! -f "$ref" ] && return
+  local tmp="${CFG_PATH}/system.cfg.merge"
+  cp "${CFG_PATH}/system.cfg" "$tmp"
+  while IFS='=' read -r key value; do
+    [[ -z "$key" || "$key" = \#* ]] && continue
+    if ! grep -q "^${key}=" "$tmp" 2>/dev/null; then
+      echo "${key}=${value}" >> "$tmp"
+    fi
+  done < "$ref"
+  sort "$tmp" > "${CFG_PATH}/system.cfg"
+  rm -f "$tmp"
+}
+
 verify() {
   TYPE=$(grep a ${CFG_PATH}/system.cfg 2>&1)
   if [[ "${TYPE}" =~ binary ]]; then
     restore
   fi
 
-  # Check if any configs are missing and restore everything if they are
+  # Restore retroarch configs if missing entirely
   if [ ! -s /storage/.config/retroarch/retroarch-core-options.cfg ] || \
-     [ ! -s /storage/.config/retroarch/retroarch.cfg ] || \
-     ! grep -q system.hostname /storage/.config/system/configs/system.cfg; then
-    rsync -a /usr/config/ /storage/.config
+     [ ! -s /storage/.config/retroarch/retroarch.cfg ]; then
+    rsync -a /usr/config/retroarch/ /storage/.config/retroarch/
+  fi
+
+  # If system.cfg is missing critical settings (e.g. after a hard crash
+  # that truncated the file), merge any missing keys from the reference
+  # config rather than overwriting all user settings with rsync.
+  if ! grep -q system.hostname ${CFG_PATH}/system.cfg 2>/dev/null; then
+    merge_missing_settings
   fi
 }