this seems to work properly

gistfile1.txt

body common control {
    bundlesequence => { "update" };
}

bundle common g {
vars:
    "sandbox_lockfile" string => "/var/cfengine/sandbox";
    has_branch.cf_test::
        "message" string => "I am a test machine";
    has_branch.cf_prod.!cf_test::
        "message" string => "I am a prod machine";
classes:
    "cf_test" expression => fileexists("$(sandbox_lockfile)");
    "cf_prod" expression => "!cf_test";
    "has_branch" expression => "any";
}

bundle agent update {

files:
    cf_prod::
        "$(g.sandbox_lockfile)"
	    delete => cleanup;
    cf_test.!cf_prod::
        "$(g.sandbox_lockfile)"
	    create => "true";
reports:
    cfengine::
        "$(g.message)";
}

body delete cleanup {
    dirlinks => "tidy";
    rmdirs => "true";
}