Leave an unchanged SteamVR driver in place when reinstalling

Re-running the installer replaced the ft_pointer driver's files under a
running SteamVR. SteamVR then kept giving the virtual controller its hand
role but ignored its laser claim, so the mouse moved its dot without
SteamVR's laser until SteamVR restarted. The driver is now staged and only
replaced when it changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pointer/driver/install.sh

@@ -18,13 +18,21 @@ reg='/opt/steamvr/bin/linuxarm64/vrpathreg'
 case ${1:-install} in
   install)
     "$root/scripts/sync.sh" >/dev/null
+    # Replacing the files of a driver SteamVR has loaded leaves its input bindings in a bad
+    # state (the 3D mouse no longer gets the laser) until SteamVR restarts, so an unchanged
+    # driver is left alone.
     "$frame" --host "set -e; test -f $src/build/driver_ft_pointer.so
-rm -rf $dest; mkdir -p $dest/bin/linuxarm64
-cp -r $src/ft_pointer/. $dest/
-cp $src/build/driver_ft_pointer.so $dest/bin/linuxarm64/
+rm -rf $dest.new; mkdir -p $dest.new/bin/linuxarm64
+cp -r $src/ft_pointer/. $dest.new/
+cp $src/build/driver_ft_pointer.so $dest.new/bin/linuxarm64/
+if [ -d $dest ] && diff -r -q $dest $dest.new >/dev/null; then
+  rm -rf $dest.new; echo 'driver unchanged'
+else
+  rm -rf $dest; mv $dest.new $dest
+  echo 'installed; restart SteamVR to load it'
+fi
 LD_LIBRARY_PATH=/opt/steamvr/bin/linuxarm64 $reg adddriver $dest
-LD_LIBRARY_PATH=/opt/steamvr/bin/linuxarm64 $reg show | grep -A3 -i 'external'
-echo 'installed; restart SteamVR to load it'" ;;
+LD_LIBRARY_PATH=/opt/steamvr/bin/linuxarm64 $reg show | grep -A3 -i 'external'" ;;
   uninstall)
     "$frame" --host "LD_LIBRARY_PATH=/opt/steamvr/bin/linuxarm64 $reg removedriver $dest; rm -rf $dest; echo 'removed; restart SteamVR to unload it'" ;;
   send)