--- /dev/null
+#!/bin/sh -eu
+tool=$(readlink -e "${0%/*}/..")
+. "$tool"/local/lib.sh
+
+cd "$tool"
+git config --replace branch.master.remote .
+git config --replace branch.master.merge refs/remotes/master
+install -m 770 /dev/stdin \
+ .git/hooks/post-update <<-EOF
+ #!/bin/sh -efux
+ case \$1 in
+ (refs/remotes/master)
+ cd ..
+ git --git-dir=\$PWD/.git checkout -f -B master remotes/master
+ git --git-dir=\$PWD/.git clean -f -d -x
+ ;;
+ esac
+ EOF